MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM ACADEMY OF AGRICULTURAL SCIENCES ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ NGUYEN THI MIN RESEARCH ON THE BREEDING OF DIPLOID HYBRID MULBERRY VARIETY F1 FOR THE NORTHERN PROVINCES OF VIETNAM Major: Plant genetics and breeding Code: 9.62.01.11 DOCTORAL THESIS SUMMARY OF AGRICULTURE Hanoi, 2018 The doctoral thesis was completed in: VIETNAM ACADEMY OF AGRICULTURAL SCIENCES Supervisors: PGS.TS Ha Van Phuc TS Nguyen Tat Khang Objection 1: Objection 2: Objection 3: The Doctoral thesis is defended at Institute Committee of PhD Dissertation Examination: VIETNAM ACADEMY OF AGRICULTURAL SCIENCES At .day month 2018 PhD thesis can be found at: - National Library of Vietnam - Library of vietnam academy of agricultural sciences INTRODUCTION Rationale Silk is a natural fiber made from mulberry silkworm (Bombyx Mori L.) that feeds on mulberry leaves and synthesizes the proteins in mulberry leaves to form cocoons of silk length of 700-800 meters (multi-ploid varieties), or more than 1000 meters (diploid varieties) Silk yarns and silk products have very precious properties such as nonconductive, moisture-draining, spongy, glossy and soft Wearing silk clothes feels cool in the summer but feels warmer than other fabrics in the winter Since silk has such precious properties, since ancient times, man has given silk yarn "the queen of textile" At the 18th International Silk Conference, Silvio Silva, president of the International Silk Association, assessed the value of silk: "After more than 4,000 years of existence, silk has been the only fiber of intermittent length Since the beginning of time, silk does not depend on any artificial energy industry, nor does it produce any pollutants Silk is a jewelry of weave industry With its historical and literature values, silk will still be loved for a long time" (Vietnam Silkworm Corporation, 1993) Silk yarns, beside being used to make garments, also produces some of the byproducts that are processed into many valuable commodities for human life, such as extracts of chlorophyll from silkworm to produce medicine, production of Lingzhi mushrooms, silkworms to produce carnations In our country, mulberry has many favorable conditions to develop the mulberry industry such as an abundant source of secondary labor in rural areas and mulberry leafpicking is suitable for both children and the elders The land available for growing mulberries in the Northern Delta is currently about 19,000 That land area is currently planting crops that are not highly economic such as maize, sweet potato and cassava The climate in our country is favorable for mulberry growing year-round, so in a year 810 silkworm crops can be harvested Meanwhile, in some temperate countries, only 4-5 silkworms are harvested in a year Moreover, the cost of investing in mulberry production is not expensive but the return of capital is fast On average, silkworms can be harvested every 20-25 days to sell cocoons Compared with rice cultivation, silkworm mulberry grows 3.5 times more profit But if the incubation is taken into account, the profit is times higher than that of rice (Ha Van Phuc, 2013) Beside various advantageous potentials, the mulberry industry in Vietnam still has low cocoon productivity per hectare, so the total income is only 80 million (Le Hong Van, 2013) while the average income per hectare in Guangdong, Guangxi (China) with the same climatic conditions as the Red River Delta is 150 million VND (Zhu Fang Rong, 2010) Furthermore, the labor used in harvesting mulberry and silkworm is growing, so the value is getting lower Over the past years, Vietnamese scientists have chosen to crossbreed and plant some new mulberry varieties such as the triploid variety (3n = 42), the cloned varieties 7, 11, 12, 28 (Ha Van Phuc, 1994) and the triploid varieties VH9, VH13, VH15 (Ha Van Phuc et al., 2002, 2003, 2009) These new mulberry varieties have changed the structure of mulberry varieties and contribute to improve the economic efficiency of production However, the new mulberry varieties mentioned above are multi-merino varieties, in addition to the advantages of yield and leaf quality, they have spongy trunks and branches, resulting in severe borer damage caused by worms, and the ability to regenerate after cutting the branches is not so good that it hinders harvesting by cutting Moreover, in order to breed a triploid mulberry variety, it is necessary to use the tetraploid variety (4n = 56) as the starting materials However, currently there is only one tetraploid mulberry variety, which is DB86, so the crossbreeding to create new varieties to select is limited Originated from that fact, we have chosen the topic: "Research on the breeding of diploid hybrid mulberry variety F1 for the Northern provinces of Vietnam" Objectives and requirements of the dissertation To create the diploid hybrid mulberry variety with higher leaf yield and better leaf quality than or equivalent to VH13 mulberry varieties, suitable for the climate and land conditions in northern provinces of Vietnam The scientific and practical significance of the topic 3.1 The scientific significance of the topic - Along with a number of results of the research on the selection of VH9, VH13 and VH15 seedlings, the results of this research will be the scientific basis to confirm that creating new mulberry varieties by natural crossbreeding is superior to cloned crossbreeding - To open new research direction, which is to use hybrid advantage to select diploid mulberry variety planted by seeds - To asset the great value in the use of imported mulberry varieties as starting materials for breeding, especially the imported mulberry varieties from Guangdong, Guangxi (China) - Initially, to determine the effect of leaf harvesting method by cutting branches, so that the new research direction is to select the mulberry varieties suitable with cutting branches to reduce labor costs in harvesting mulberry and silkworm growing 3.2 The practical significance of the topic - To select some mulberry varieties as starting materials - The results of the dissertation will create new varieties of mulberry for production, contributing to the increase in productivity of silkworm cocoons - To identify suitable ecological zones for new mulberry varieties to promote the superiority of varieties - To evaluate the regeneration capacity of new varieties and the direction of branch cutting New findings of the dissertation The new mulberry varieties in our country since 1996 are produced by the hybrid method between diploid and tetraploid mulberry varieties to create triploid varieties However, this research was carried out in the direction of selecting diploid seeds using the natural hybrid method This study wants to select new varieties for the Northern provinces to meet the requirements of the topic Structure of the dissertation The dissertation consists of 143 A4 -size pages including 64 tables, figures The dissertation includes the Introduction (5 pages); Overview (38 pages); Materials, contents, methodology (10 pages); Results and discussion (88 pages); Conclusions and recommendations (2 pages) This study cites 110 documents in total, including 32 Vietnamese, 62 English and 16 Chinese papers CHAPTER I: OVERVIEW OF THE MATERIALS AND SCIENTIFIC BASIS OF THE DISSERTATION 1.1 The scientific basis of the topic Bombyx Mori L only eats mulberry leaves Therefore, yield and quality of mulberry leaves are closely related to yield and quality of cocoons (Ha Van Phuc, 2003) Moreover, over 60% of the cost of producing cocoons is used to grow, care for and harvest mulberry leaves (Deng Wen et al., 2010) Thus, mulberry leaves also significantly affect the cost of cocoon production The yield and quality of mulberry leaves depend on many factors such as soil condition, climate, cultivation methods, harvesting, etc., but mulberry is a very influential factor Today mulberry is considered as a means of production 1.2 Study on breeding new mulberry varieties 1.2.1 Studies in the world 1.2.1.1 Study on the breeding of cloned multiplication varieties Mulberry is a wood-getting tree, which has strong rooting characteristics when planting by branches in suitable crop Cloned varieties always keep the genetic traits of the breed through generations Natural hybridization is the hybridization of genes between father and mother breeds, from which hybrid mulberry trees inherit good genes Good individuals selected through cloned hybridization will maintain these traits In 1967, the silkworm experiments of the Ministry of Agriculture, Forestry and Fisheries of Japan (Zheng Mong Xia, 1987) crossbred two local mulberry varieties, Ichinoxe and Cailieunemi to create the new variety Xinichinocar This new mulberry variety has overcome the drawback of the Ichinoxe, so it is suitable for harvesting mulberry leaves by cutting branches The mulberry grows well, yielding 12% higher yield than the parent mulberry varieties However, through planting in the production areas, the new mulberry variety has the disadvantage of being susceptible to viral diseases and dry black bacteria To overcome this disadvantage of the new mulberry variety, in 1976 the Japanese breeders have hybridized the Xinichinocar with the Kokyco 21 variety and chose the "Nan Mery" variety This new variety retains the good characteristics of the Xinchinocar, but it has the potential to overcome the bacterial and viral susceptibility Indian breeders Das et al (2006) selected a number of promising hybrids from hybrid combinations of Morus India, Morus Latifolia and Morus Multicaulis with M.Alba, Morus Rotundiloba He said that the parent varieties participating in the hybrids are far from each other in terms of geographical conditions and traits, so hybrid F1 generations exhibit manifold traits Therefore, it is necessary to select individuals to find the mulberry trees to meet the target selection Yang Fing Hoa et al (2012) at the Chinese Mulberry Research Institute has combined the Lake 39 mulberry planted in the Zhejiang province with a temperate climate with Guangdong subterranean mercury having a subtropical climate The result was that seedlings No had spring germination properties similar to Lake 39 Straight and multi-branch shoots were suitable for cutting method, good resistance to bacterial and viral diseases but feasible However, cold tolerance of this variety is less than that of the Lake 39 one This new mulberry variety has grown widely in Zhejiang and Fujian provinces Since 1994, scientists from the Guangdong Chinese Silkworm Research Institute (Sun Xiao-Xia et al., 2013) have crossbred the line between the 408th Chineseoriginated Bulgarian mussel variety with early spring germ inability, high germination rate, big and thick leaves, healthy growth of mulberry trees Lake No sprouts late spring, has large and thick leaves, and is resistant to viral and bacterial diseases The result was selected new breed called "72 - 1" has the advantage of spring germination earlier than Lake one The mulberry grows strong, has short internode, big and thick leaves Leaf yields were 23-41% higher than control varieties The quality of the leaves should be increased by 15% compared to the control varieties According to Wang Hong-Chi (1987) and Malli Krafunappa (1992), from the 1950s through the use of crossbreeding between mulberry varieties with geographic origins, Chinese researchers has selected many high yielding varieties such as No 2, Chinese Variety 5801, 6031 original Chinese Variety, Lake Seed No and Seed No 11, etc 1.2.1.2 Use of natural hybrid production to create seedlings Cloned varieties besides various advantages described above, there are some disadvantages such as the rate of plants are low because it depends on the ability of the seed, planting time and some other techniques The root system of the mulberry grows poorly, so it is resistant to external conditions, especially in drought conditions From this fact, the breeders have turned to breeding for mulberry seed From the 1930s, some researchers from the Soviet Union such as Dien Ren Co, Bytenko, Kytro-Ka-Rop (Ha Van Phuc, 2003) selected F1 hybrid dipterocarp seeds due to the hybrid combination of local mulberry varieties with Japanese imported varieties, the results have selected a number of suitable varieties grown in the north such as San Nhit17 hybrid with Pionhski, the Lixi hybrid with Pionhski, Bobetda hybrid with Pionhski For the southern climate is the San-nhit 15 hybrid with Pionhski (Ha Van Phuc, 2003) Leaf productivity of hybrid mulberry varieties was higher than that of local mulberry varieties from 28 to 54.20% From 12 diploid F1 hybrids, Bulgarian breeder Bulgarian PenKob and their colleagues selected the hybrid varieties No 117 with No 118 and No 117 with No 120 for leaf growth of 12.2 - 24.5 % compared with old mulberry varieties (According to Ha Van Phuc, 2003) Multi-seed F1 hybrid multiplication was also investigated later than diploid variety Zhen Fu- Zhao et al (1999) have chosen to produce the second seed of the Guangdong seedlings, which yields higher leaf yields than the dipterocarp cultivar Better leaf quality, the silkworms fed on this mulberry leaves have 9.22% more cocoon yield, the number of eggs increased by 26.4% In 1999, scientists from the Guangxi Mushroom Research Institute (Zhu Fang Rong 2012, Luy fu Sheng 2011) created 10 pairs of triploid varieties and two tetraploid hybrid varieties (4n = 56) 1.2.1.3 Use of mutagenic agents to produce mulberry varieties Mutations in mulberry plants can also occur in natural conditions, but at a very low rate In the field of modern breeding, humans have used a number of physical and chemical agents to generate genetic variations in many different crops In the field of breeding mutant mulberry, Japan and India have done earlier and achieved some meaningful achievements, created some mutant varieties such as IRB240-1, IRB240-5, S54 (Sugiyama T.1962, Katagiri and CS 1990) China has started to research in this direction since 1960s Sichuan Mulberry Research Institute has used the γ emitter from Co60 to harvest mulberry, which obtained broad adaptive mutation 7681, healthy mulberry plant (Lin Tai-Kang, 1987) Zhejin Research Institute for Radiation Oncology has shown radiation on the Xinjiang iris tree and created the tetraploid mutant (4n = 56) R81-1 and R81-2 This mutation is resistant to bacterial disease and has good leaf quality (Loguoshi et al., 2011) Materials used to irradiate γ in mulberry trees are pollen, mulberry seed, strawberry sprout and strawberry branch The research shows that the use of cuttings and mulberry plants are more effective mutation According to Lin Tai-Kang and CS (2011), the appropriate dose of x-ray irradiation in the mulberry tree was 10,000-11,000 R, the strawberry variety was 10,000 R, the dried mulberry seed was 40,000 R, and the pollen was 4,000 R 1.2.2 Research on the breeding of mulberry in Vietnam 1.2.2.1 Causing mutation Mulberry growing in our country has a long history, but research on silkworm breeding has only started in 1964 and we have been breeding mulberry since 1970 In this period, they used a number of chemical agents such as Colchicines and irradiated γ radiation on the seeds of the local mulberry breed of Ha Bac with doses ranging from 2,000 to 10,000 have received the mutation in the dose of 7,000 to 10,000 R The authors named these mutations 2R7, 1R10 and 2R10 (Ha Van Phuc et al., 1994) In the 2R10 form of mosaic, the variety had two types of leaves in the tree Nguyen Van Vinh (1996, 1997) also treated γ rays into cuttings of the Indian variety VA186 and Bao Loc’s variety Bau Den with a dosage of Krad to 10 Krad The author also invitro mulberry plants with a dose of 0.5 to 4.5 Krad The result of this study was the selection of mutant lines from Bau Den mulberry variety namely B93-1, B93-2, B93-3, B-16, B-17, B-18 and lines from VA186 mulberry VA93- 5; VA93-8; VA-12; VA-15 and VA-18 from VA-186 Just like the results above, these mutations are only different from primitive varieties of leaf morphology, branch shoots, etc From the above results, the direction of selection of mutant mulch by irradiation method γ was not oriented to the result of breeding for human purpose 1.2.2.2 Creating the multi-harvest varieties of mulberry From the combination of C71A mutation caused by colchicines treatment, in 1972, author Ha Van Phuc and his colleagues have hybridized some local mulberry varieties such as Chan Vit, Quang Bieu and Ngai to create new mulberry triploid varieties 7, 11 and 12 (Ha Van Phuc et al., 1994) The results of field trials in some localities in the Northern Delta show that all three new mulberry varieties have the advantage that those mulberry varieties grow stronger than the C71A tetraploid, the large leaf size and thicker than the diploid varieties that are involved in the hybrids, Chan Vit, Quang Bieu and Ngai Leaf productivity of new varieties No 7, No 11 and No 12 were 10-15% higher than those of control Due to the leafy foliage, leaf quality through silkworm rising gave higher cocoon productivity (Ha Van Phuc, Nguyen Thi Tam, 1986) These new mulberry varieties are well rooted so clonally propagation rate is over 90% Results of the trial showed that the variety No 11 suitable for saline soils in the coastal areas, No 12 varieties can grow in the mulberry growing areas of the Northern Delta Only No varieties are resistant to Brassica and are well adapted to the Central Highlands such as Lam Dong According to the report of Lam Dong Son Lam Agricultural Experiment Center (Phan Dinh Son et al., 1995), (Le Quy Tuyen - PhD in agriculture, Hanoi 2013), No mulberry varietiy are being expanded in the Central Highlands such as Lam Dong, Dak Nong, In 2013, the Bao Loc-Lam Dong Agricultural Research Center conducted a trial of hybrid mulberry TBL03 and TBL05 in some production areas in Dak Nong and Lam Dong Both breeds were formed by hybridization between local Lam Dong mulberry varieties and imported varieties from Guangdong province, China The results showed that leaf yield of these new mulberry varieties was higher than that of control variety VA201 from 13.7 to 22.4%, leaf quality was equivalent to that of Bau Den variety in Bao Loc 1.2.2.3 Creation of hybrid mulatto varieties (seeds) Due to the disadvantage of cloned varieties (seed cuttings), since 1996, author Ha Van Phuc has shifted to the direction of crossbreeding varieties by natural hybridization From 20 combinations of mulberry, Ha Van Phuc et al (2002) selected three varieties of mulberry hybrids: VH9 and VH13 both yielded higher leaf yields than those of mulberry variety No 12 12.5%, and 6% higher than that of Chinese imported mulberry seed (Ha Van Phuc, 2003) In 2012, the seedlings of VH15 seedlings have high leaf yield, high leaf yields are added to production (Vu Duc Ban, Ha Van Phuc et al.) Application to the production of seed mulberry varieties have changed the farming practices in the planting season In the past, when growing varieties of cloned breeds, the planting season is only in the mid-November to the end of December But for the varieties of mulatto seed multiplication, the planting season lasts from January to November In addition, mulberry varieties grown from seeds are very adaptable to climate and land conditions In summary, nearly half a century ago, the work of researching new mulberry varieties in our country has been in the direction of breeding mulberry seedlings, diploid multiplication clones with sexual duplication In this thesis we will present the results of selection of hybrid breeding mulberry CHAPTER II MATERIALS, CONTENTS AND METHODOLOGY 2.1 Study Materials Research materials include: 12 imported varieties of mulberry, as follow: - varieties of Chinese origin are: K9, K10, K11, Q1, Q2, No 2, No 3, DB1, DB2 - mulberry varieties of Indian origin: IA - varieties of Vietnamese origin: Ngai, Ha Bac - 10 combinations of F1 mulberry made by crossbreeding including VH18, VH19, VH20, VH24, VH25, GQ1, GQ2 - The reference variety mulberry VH13 is a new mulberry variety, approved by the Ministry of Agriculture in 2006, which is made up of the hybrid variety IA originating in India with the cultivar DB84 of Vietnamese origin - GQ2218 double-glazed silkworms and hybrid yellow silkworms (ĐSK × TQ) 2.2 Research content 2.2.1 Study on assessment of some mulberry varieties used as starting materials and crossbreeding to create new hybrid combinations 2.2.2 Comparison and selection of new hybrid breeding 2.1.2.1 Study on the growth, composition and leaf productivity of hybrid combinations 2.2.2.2 Degree of infection of some major diseases 2.2.3 Selected comparisons of some promising hybrid combinations 2.2.3.1 The study identified several factors that contributed to yield, leaf productivity and levels of some key pests and diseases 2.2.3.2 Quality inspection of mulberry leaves through silkworm rising 2.2.4 Study the effect of cuttings on composition and leaf yield of GQ2 2.2.5 Adaptation of GQ2 in some ecological areas of Northern provinces 2.2.5.1 Experiment on some components of yield and leaf productivity of GQ2 2.2.5.2 Adaptive and stable assessment of the GQ2 variety 2.3 Methodologies 2.3.1 Evaluation of some mulberry varieties used as starting materials - Implementation time: 2006 - 2008 - Study location: Ngoc Thuy, Gia Lam, Hanoi on alluvial soil not accreted - Methodology: The mulberry seedlings were grown in the seed group at the planting distance of 1.5m x 0.3m Each variety planted 20 plants, not repeated Planted in 2006 2.3.2 Natural hybrid combinations - Time for implementation in January - March 2009 - Hybridization method: + The mulberry varieties selected to participate in crossbreeding are grown in the group of mulberry varieties in Ngoc Thuy, Long Bien, Hanoi and Viet Hung, Vu Thu, Thai Binh The distance is 1.5m x 0.3m Each variety planted 20 plants, not repeated Planting time is in 2006 - Regarding organic fertilizer: 25 tons/ha/year, once in December, NPK ratio is 16.5:7:7, 2000 kg NPK/ha/year, which is fertilized in January, April, July and September + In the winter of 2008, all the mulberries are not cut, only cut the tops from 1015cm, marked and hang the sign of the name + In the spring of 2009, when the mulberry trees sprout the flower buds, using paper bags cover the strong branches of the breed to isolate the intersection After observing that female and male flowers of hatching parent breeds reached more than 70%, cut the branches of the male flowers in isolation bags of the female flowers and tie them to the branches After 2-3 days of pollination, the flower stamens from white to light yellow, then pocketed isolate, cut off a few female flowers due to late bloom so not pollinated Use the pollen wrap to wrap mulberry pollen and protect the berries When ripe berries are dark purple, take fruit, split strawberries and sow in the pot The regime of mulberry tree care in the pots of hybrid combinations is uniform When the mulberry tree grows in the height of 20-25cm, it will be planted in the field at each replication of the hybrid 2.3.3 Composite selection for hybrid combinations - Implementation time: July 2009 to December 2011 Mulberry is planted since May 2009 In 2010, mulberry trees were cut in winter crop, in 2011, cut in the summer - Study location: Ngoc Thuy, Gia Lam, Hanoi - Hybrids selection method: based on population selection, based on some indicators of productivity, productivity and level of infection of some major diseases to select the promising hybrid combinations - Experimental methods: The experiment was arranged in a randomized complete block of replicates, each repeating the planting of 40 trees on the same row The planting distance is 1.20x0.3 m The regimes of care for mulberry trees are uniform among varieties and repeated 2.3.4 Study on comparison of some promising hybrid varieties After two years of research on 10 combinations of mulberry, it is based on the results obtained on the criteria of composition, yield, leaf , to select four most promising hybrid combinations for basic testing 2.3.4.1 Field experiment method - Implementation time: July 2011 to December 2014 - Location: Ngoc Thuy, Long Bien, Hanoi + The experiment was arranged by the method of random block complete repeated times, each time planted 30m2 The planting distance is 1.20x0.3 m The regimes of care for mulberry trees are uniform among varieties, repeated Planted since May 2011 2.3.4.2 Laboratory methods: + Silkworm evaluation of leaf hybrids of all spring, summer and autumn crops was carried out Spring and the second silkworm growing GQ2218, the summer breeding of multi-hybrid silkworm (WK × China) - Methods: combinations of mulberry and control mulberry varieties were treatments Each formula feeds silkworms aged 4, each with 300 silkworms Silkworms from to years old gave silkworms the same leaves of mulberry varieties not in the experiment (mulberry No28) Silk worms from the age of to the ripe silkworm fed the leaves of hybrid combinations with the number of mulberry leaves are weighed each meal to ensure the formula has the same amount of mulberry leaves Fecal work, silkworm care, sleep, ensure uniformity in formulas When the silkworm is ripe, the silkweed will be shuffled into each replicate of the experiment 2.3.5 Study on the effect of cuttings on composition and leaf yield of GQ2 Implementation time: 2015-2016, strawberry plantation in 2013 Location: Ngoc Thuy, Long Bien, Hanoi Research Methods: - The experiment was arranged by complete block method Area of each cell is 30m , times to lift The experiment consists of formulas: 1: Cut branches once on April - 2015 Then pick leaves on 2/6, 18/6, 14/8 and 9/10 2: Cut branches twice, the first time on April 2015, the second on 18/6, then the next on 14/8 and 9/10 3: Cut branch times, first on April 4, 2015, the second on June 18 th, the third on August 14th, then picked the leaves on October 9th 4: Foliage control (control) 2.3.6 Study on the adaptation of GQ2 variety in some parts of northern Vietnam 2.3.6.1 Leaf yield test Implementation period: from 2012-2014 - Materials: GQ2 mulberry variety, VH13 mulberry variety - Trial location: + Silkworm silkworm mills (Son La) + Tinh Cuong Cooperative, Cam Khe, Phu Tho the control varieties hybrid VH25 hybrid exceeds 52%, VH18-27% GQ2- 16% and VH19-12% 3.3.1.2 Germination in the autumn In the autumn season, the number of germination germs of hybrid combinations ranged from 30.60 to 53.70 germination and effective germination was 11.67 to 16.02 germination The control variety VH13 has the number of germination germs of 35.30 germination, the effective germination number is 14.25 germ Compared to the hybrid variety VH13, crossbreds had higher yields than the control varieties including GQ2 12.42%, VH21-8.98%, GQ1 - 7.09%, VH19-6, 74% The remaining combinations are equal to or lower than the control varieties 3.3.1.3 Some indicators on leaves - Leaf size includes leaf length and width Leaf size is related to the yield of mulberry leaves, while also affecting labor productivity when harvesting leaves Table 3.1 Average size of mulberry leaves in crops of hybrid combinations (Unit of account: cm, %) % compared to control varieties Hybrid Leaf length (cm) Leaf width (cm) complex Length Width VH18 VH19 VH20 VH21 VH22 VH23 VH24 VH25 GQ1 GQ2 VH13 (đ/c) 17,14±0,21 16,85±0,16 15,25±0,19 16,49±0,18 17,46±0,20 17,78±0,26 16,49±0,23 15,45±0,15 17,96±0,18 17,94±0,20 15,25±0,15 14,60±0,12 14,±0,12 13,73±0,11 14,50±0,13 14,97±0,17 14,90±0,16 14,54±0,14 13,63±0,12 15,36±0,17 15,84±0,14 14,00±0,13 104 104 98 104 106 106 103 97 110 113 100 (Data in 2010) The data in Table shows that except that the VH20 and VH25 hybrid combinations have the same leaf size as the control mulch VH13, the remaining hybrid combinations have a larger leaf size than the control In which the GQ1 and GQ2 hybrids had the largest leaf size, the leaf length was 18% higher than the control variety, the leaf width increased by 10-13%, followed by the VH22 and VH23 hybrid leaf lengths increased from 14-17%, width increased by 6% - Number of leaves per meter of branch: The number of leaves per meter depends on the length of internode on the branch, the longer the internode, the fewer the number of leaves per meter The data obtained in the experiments show that hybrid combinations of VH20, VH25 and VH24 have more leaf numbers than the control varieties of 3.26-8.28%, GQ1, GQ2, VH21, VH18 all had 3-14.6% fewer leaves, indicating that these hybrid combinations have long internodes - Leaf mass per meter: The leaf mass per meter of sprouts reflects the branching length, leaf size and thickness and is closely related to leaf productivity In 10 hybrid combinations, VH25 11 112 110 100 108 114 117 108 101 118 118 100 had lower leaf volume than the control sample of 6% The remaining hybrid combinations have leaf mass per meter increase from 6-12% compared to control varieties, of which hybrid GQ2 increased 20%, followed by GQ1, VH19 and VH20 increased from 13-17% The remaining hybrid combinations increased from 4-7% The hybrid combinations have higher leaf weights per meter than control varieties due to their large leaf size as shown in the table above 3.3.3 Leaf yield Leaf yield is the composite indicator of the components of leaf productivity, to increase the total income per unit of area that has to improve cocoon production The most important factor affecting cocoon production is the yield of mulberry leaves Table 3.2 Yield of hybrid mulberry leaves of Unit of Account: kg/100m2, % Name of Spring harvest Summer harvest Fall harvest Total CSSS hybrid species VH18 88.94 213.68 73.29 375.91 118.42 VH19 68.60 222.35 58.40 349.35 110.06 VH20 76.26 199.83 55.90 331.99 104.57 VH21 56.43 214.84 41.93 313.20 98.67 VH22 59.68 196.94 48.48 305.10 96.12 VH23 57.83 184.98 52.47 295.28 93.02 VH24 60.91 207.28 46.28 314.47 99.07 VH25 70.64 195.68 48.36 314.68 99.13 GQ1 76.78 213.63 51.80 348.47 109.78 GQ2 79.78 210.00 74.28 364.69 114.89 VH13 69.51 189.35 58.57 317.43 100.00 CV(%) 9.77 7.29 9.57 LSD(0,05) 8.69 10.06 6.78 Data in 2010 Total annual yield of hybrid combinations ranges from 295.28 kg to 375.91 kg over 100m2 Among them, the highest yield was VH18 and GQ2, which are 375.91 kg and 364.69 kg respectively, followed by hybrid VH19 and GQ1 with 349.35 kg and 348.69 kg respectively Productivity of Mulberry leaf (% compared to control variety) Name of cross combinations Figure 3.2 % leaf yield compared to the control of cross combinations 12 3.3.4 Infection degree of dangerous diseases - Phyllactinia moricola usually occurs in low temperature and high humidity period Diseases cause the leaf quality to decrease and the consumption ratio of mulberry leaves increases for cocoon The results show that all cross combinations and mulberry varieties are infected with Phyllactinia moricola but differed in severity On average of spring and autumn crops, the infection of Phyllactinia moricola disease in cross combinations ranges from 13.80% to 19.43%, the disease index is 4.85-8.64%, and the control variety VH13 has the corresponding figures 12.99% and 4.02%, respectively Thus, the control variety VH13 is less susceptible than cross combinations - Level of virus infection Virus is the most dangerous disease for mulberry plants since there is no medication or treatment available, but the main measure to limit the disease is the selection of mulberry varieties and cultivation methods The results of the spring and autumn crops show that all cross combinations and the control variety are infected, of which VH20 and VH25 have the highest rates of disease which are 13.48% and 13%.87% respectively, VH22 and VH23 have the same disease rate as the control varieties, the remaining cross combinations have lower rate Degree of Virus infection ((% compared to control variety) Name of cross combinations Figure 3.3 Percentage of mulberry plants infected with Virus disease in cross combinations compared to the control variety Based on the synthetic results of productivity and leaf yield indexes, we selected four promising cross combinations, VH19, VH20, GQ1 and GQ2 to conduct a basis and detailed evaluation of advantages and disadvantages of each variety 3.4 Comparison and selection of promising cross combinations 3.4.1 Factors contributing to the yield of mulberry leaves - Germination time in Spring crop In the spring of 2013, from January to 13, the mulberry trees of the cross combinations began to germinate According to calculations, it was not until January 22 that GQ1 and GQ2 cross combinations reached over 50% germination, which is the time of germination of these two cross combinations VH19 and VH20 have their germination on January 28 As for the control variety VH13, the germination time is on February Thus, GQ1 and GQ2 have their germination time 12 days earlier compared to the control variety and days compared to VH19 and VH20 This result reaffirms that the early germination characteristics of the dominant mulberry varieties in hybrid mulberry trees 13 - Size of leaf blade Our collected data show that in all three crops including spring, summer and autumn, leaf length and width of hybrid combinations were significantly higher than that of the control variety VH13 The average leaf length and width in crops of cross combinations in comparison with the control variety are shown in Figure 3.4 % width compared to control variety % length compared to control variety Figure 3.4 Average leaf length and width in crops of cross combinations in comparison with the control variety The data in Figure shows that GQ2 has the largest leaf size; its length and width exceed the control variety with 13% and 8% and VH19 with 13% and 9% respectively, followed by VH20 with 11% and 4%, and GQ1 with 7% - The number of leaves in 500g Table 3.3 The number of leaves in 500g (Unit: leaf, %) The number of leaves in 500g in % crops compared Cross Average of No to the combination crops control Spring Summer Autumn variety VH19 239.33 174.00 366.00 259.78 93 VH20 235.33 1.67 415.00 268.67 96 GQ1 232.00 140.30 359.67 244.00 87 GQ2 243.00 142.00 294.00 226.30 81 VH13 251.00 241.33 345.67 279.33 100 CV (%) 7.71 7.29 7.02 LSD 0,05 2.88 16.69 33.52 The data in the table clearly indicate that leaves of cross combinations are large, so the number of leaves in 500g in crops spring, summer and autumn is less than the control variety GQ2 has fewer leaves than the control variety at 19% and less than GQ1 at 13% The remaining two cross combinations are less than 4-7% - Stem growth Stem growth is the most influential factor in the yield of mulberry leaves This indicator impacts on some factors such as soil fertility, care regime, rainfall, temperature, etc in which mulberry varieties are significantly affected The stem growth is shown in tree height, stem diameter and total length of stem 14 Table 3.4 Some indicators of stem (Unit: cm, stem, %) Tree Cross No height combination (cm) VH19 VH20 GQ1 GQ2 VH13 264.67 258.40 274.62 272.27 250.73 Total length of stems Number on a tree (cm) Number Average of Diameter of firstTotal stem % height of second- of firstlevel length / compared stem level level stem stem tree to the (cm) stem (cm) (stem) control (stem) variety 1940.73 108 102.30 7.47 11.60 1.85 1836.50 103 90.02 7.80 12.60 1.96 1907.45 107 92.19 8.15 12.54 1.95 1996.83 112 104.53 7.30 12.80 1.98 1782.97 100 106.76 5.90 10.80 1.70 Data in table 3.4 shows that the growth rate of germ in crops of cross combinations is higher than that of the control variety Trees of the four cross combinations are higher than those of the control variety The number of stems and the stem length of the cross combinations are higher, so the total length of stems in all four cross combinations is higher than that of the control variety at 2-12% The total length of the biggest stem is 1996.13cm, exceeding the control variety with 12%, followed by VH19 and GQ1 increasing 8% and 7% respectively 3.4.2 Leaf yield and quality of promising cross combinations The data in the table indicate that in the spring and summer crops, the yield of cross combinations is higher than that of the control variety, but only GQ2 and VH20 cross combinations are higher in the autumn crop It is most noticeable that the yield of cross combinations is high in spring crop, in which GQ2 reaches the highest with 89.41 kg / 100m, followed by GQ2 - 79.52kg / 100 m, the control variety only reaches 65 80kg Spring and autumn crops have weather that is most suitable for bivoltine silkworm race that produce high-quality cocoon Thus, mulberry has high yield in spring and autumn crops, which is significant for improving the economic efficiency of mulberry production The comparison of annual yield of cross combinations with the control variety is shown in Figure 3.6 Figure 3.5 Leaf yield in crops of cross combinations in 2014 (Unit: kg, %) Amount of leaves in kg/100 m Cross Total amount No combination per year (kg) Spring Summer Autumn VH19 74.16 236.11 44.69 354.96 VH20 68.07 242.22 59.77 370.06 GQ1 79.52 224.68 50.83 354.68 GQ2 89.41 234.44 65.90 389.75 VH13 65.80 208.51 55.44 329.75 CV (%) 11.70 6.90 8.40 LSD 0,05 10.54 12.49 8.75 - 15 Leaf yield % compared to the control variety Cross combinations Figure 3.6 Comparison of four-year average yield of cross combinations GQ2 has the highest leaf yield, exceeds the control variety with 18%, followed by VH19 with 8%, and GQ2 with 6% VH20 is only 3% higher Table 3.6 Leaf yield of cross combinations in 2012-2015 in Ngoc Thuy-Long Bien Hanoi (Unit: Kg/100m2) % Name of compared Average Cross 2012 2013 2014 2015 to the of years combinations control variety VH19 347.70 322.91 354.96 408.81 358.60 110.61 VH20 311.92 318.00 370.06 384.06 336.01 103.64 GQ1 305.94 347.70 354.68 441.05 354.84 109.45 GQ2 331.00 369.90 389.75 409.85 375.24 115.74 VH13(control) 310.23 307.00 329.95 349.63 324.20 100 CV (%) 6.60 5.50 4.10 6.80 LSD 0,05 20.01 24.60 17.85 31.36 Data of leaf yield over years followed up show that only GQ2 and VH19 have higher yield than VH13 with the reliability level of 95% in 2012; GQ1 and VH20 show no significant difference from the control variety In 2013, only two GQ1 and GQ2 have yield reliable differences compared to control variety But in 2014 and 2015, the yield of all four cross combinations is higher than the control variety with the reliability level of 95% On average, GQ2 has the highest leaf yield, 16% higher than the control variety, and 11% higher than VH19 The remaining two cross combinations are lower than GQ2 4-9% - Leaf quality is a reflection of chemical compositions of mulberry leaves, which gives silkworms producing high-quality cocoon In order to evaluate the quality of leaves, researchers often use biochemical method which analyze leaf nutrient and biological method which is based on the results of silkworm rearing In these two methods, biological method is more common and accurate (Ha Van Phuc, 2003) We have been raising silkworms in crops a year, bivoltine silkworm race is raised in spring and autumn crops, and multivoltine silkworm race is raised in summer crop 16 Table 3.7 Cocoon productivity of cross combinations (Unit: gram, %) Spring crop Summer crop Autumn crop % % % Cross Net Net Net No combination amount compared amount compared amount compared to the to the to the (gram) (gram) (gram) control control control VH19 491.68 106.78 245.44 100.01 367.29 96.07 VH20 460.32 99.97 256.77 104.12 371.48 97.17 GQ1 483.14 104.93 248.22 100.65 393.41 102.91 GQ2 471.53 102.41 252.95 102.81 386.62 101.13 VH13 460.45 100.00 246.62 100.00 382.30 100.00 CV (%) 3.90 1.20 1.00 LSD 0,05 35.16 5.56 7.31 Data in Table 3.7 show that cocoon productivity obtained in cross combinations in three crops is different from that of the control variety VH13, but this difference is not significant The evaluation of cocoon quality by indicator of cocoon rate and some technological parameters of silk yarn also have similar results as cocoon productivity The difference in cocoon quality between cross combinations with VH13 is not significant at 95% reliability level 3.4.3 Infection level of major pests 3.4.3.1 Phyllactinia moricola disease in mulberry leaves North Delta has high humidity, so phyllacdinia moricola usually develops in spring and autumn seasons This disease reduces the quality of mulberry leaves, increasing the consumption of mulberry leaves for cocoon weight Table 3.8 Infection degree of phyllactinia moricola in spring crop of cross combinations Spring crop 2013 Spring crop 2014 2-year average Cross No combination Rate Indicator Rate Indicator Rate Indicator VH19 16.65 6.70 9.12 4.50 12.88 5.60 VH20 14.24 7.25 7.40 3.70 10.82 5.44 GQ1 14.85 6.15 10.18 5.49 12.51 5.82 GQ2 12.35 5.70 8.20 4.05 10.27 4.87 VH13(control) 6.12 2.87 5.70 3.40 5.91 3.13 The results show that in the spring crop of the two years, the disease rate and indicator in the four cross combinations are higher than that of VH13, indicating that cross combinations are hypersensitive to the disease 3.4.3.2 Level of Virus infection Production reality shows that all local varieties of mulberry, new and imported varieties are infected with virus disease with various level 17 Table 3.9 Degree of virus infection in cross combinations (Unit: tree, %) No Cross combination Number of inspected trees Summer crop Number % of infected infected trees trees Autumn crop Number % of infected infected trees trees Annual average Number % of infected infected trees trees VH19 120 15 12.50 11 9.16 10.80 72 VH20 108 12 11.11 8.83 9.70 64 GQ1 99 10 10.10 11 11.11 10.60 70 GQ2 108 11 10.18 13 12.73 11.45 76 VH13(control) 96 13 13.54 16 16.66 15.10 100 Average data obtained during the summer and autumn crops show that the percentage of mulberry plants infected with virus disease in the four cross combinations is 24-36% lower than the control variety We predict that this difference derives from the damage extent due to stem-eaten pests which we will present below 3.4.3.3 Damage level due to stem-eaten pests There are many kinds of stem-eaten pests but we observe that the northern type is Apriona Germany Hope The mulberry tree eaten by pests at the top of the tree, stem and stump are hollowed out so mulberry trees age quickly Table 3.10 Damage level due to stem-eaten pests (Unit: trees, %) Number of damaged trees Number Cross of Number of % damaged tree No % damaged combination inspected damaged compared to control tree tree tree variety VH19 120 47 39.16 62 VH20 108 51 47.22 74 GQ1 99 40 40.40 64 GQ2 108 37 34.25 54 VH13(control) 96 61 63.54 100 The data in Table 3.10 show that all four cross combinations have a lower percentage of mulberry trees damaged by stem-eaten pests compared to the control variety with 28-46% This difference is due to VH15 mulberry trees of triploid type (3n = 42), while the four cross combinations are diploid (2n = 24) According to author Ha Van Phuc (1994), the thickness of the wood in the stem, branches of multiplied mulberry varieties are much thinner than the diploid variety, but the heartwood is thicker Therefore, the stem-eaten pests love eating multiplied mulberry trees Based on the results of the comparison of the four promising cross combinations described above, we have identified that GQ2 has more advantages and has been recognized by the Scientific Council of the Ministry of Agriculture and Rural Development and allowed for trial production in mulberry fields of the Northern Delta 18 3.5 Study on the effect of branch pruning on factors contributing to productivity and yield of GQ2 mulberry leaves Based on the results of the experiments mentioned above, the regeneration characteristics of the new diploid cross combinations, including GQ2 are better than those of VH13, displayed in the number of germination, effective germs after pruning in years, all crops with higher productivity This characteristic of GQ2 is favorable for the application of pruning methods instead of leaf picking and is also applied to silkworm rearing to reduce labor 3.5.1 Impact of branch pruning on leaf growth rate and budding Table 3.11 Impact of pruning times to grow mulberry trees Date-Month Formula Pruning time Pruning times Pruning times Leaf picking (control) Indicator Length of germ (cm) Number of leaves (leaf) Length of germ (cm) Number of leaves (leaf) Length of germ (cm) Number of leaves (leaf) Length of germ (cm) Number of leaves (leaf) 24-9 (Unit: cm,leaf, %) Compared BQ/ to control date variety 4-9 9-9 14-9 19-9 0.00 2.15 8.05 13.73 16.94 0.85 185 0.00 2.00 3.50 4.70 6.10 0.31 207 0.00 2.05 9.22 12.74 15.93 0.80 174 0.00 1.93 3.40 4.27 5.07 0.25 167 0.00 3.66 15.93 26.71 36.13 1.81 393 0.00 1.93 4.27 6.33 7.93 0.40 270 0.00 1.79 5.99 8.67 9.11 0.46 100 0.00 1.60 2.73 3.13 3.13 0.15 100 Our data obtained upon pruning one time and two times are similar to pruning three times, if the increase in germ length, the number of leaves increases are relied on the number of branch pruning, the number of branch pruning increases the rate of growing germ length and the number of leaves increasing compared with the leaf picking as shown in Figure 3.7 19 Process of increasing germ length after times of pruning Germ length Leaf picking Pruning time Pruning times Pruning times Time (date/month) h) Figure 3.7 Process of increasing germ length after times of pruning The difference in growth rate and emergence of leaf between cuttings and leaf picking is due to the distance from the resin path from leaf to root and from root to leaf This distance is shorter in mulberry trees having branch pruning, allowing the germs and leaves to receive nutrients faster, so the growth rate is faster 3.5.2 Effect of branch pruning to size and thickness of leaf blade The bigger number of branch pruning is, the smaller the leaf length and width are; the formulas of branch pruning time and times have no difference, only reducing leaf length 3%, and leaf width 6% For formula of 3-time branch pruning, this indicator decreases by 11% and 15% respectively Table 3.12 Amount of 100cm2 leaves of the experimental formulas Indicator Amount of 100 cm2 leaves Time Formula After the 1st After the After the 3rd Average pruning 2nd pruning pruning Compared to control variety (%) 96 88 84 100 1st pruning 2.30 2.22 1.95 2.16 nd pruning 2.36 1.66 1.82 1.94 rd pruning 2.32 1.63 1.60 1.85 Leaf picking 2.75 2.10 1.78 2.21 (control) The thickness of leaf blade is determined by amount of 100cm2 leaf area, the larger the amount of leaf blade is, the thicker it is Data shown in Table 12 indicate that the bigger the number of branch pruning is, the smaller the amount of leaf blade is in comparison with control leaf picking formula Thus the method of harvesting mulberry leaves by branch pruning reduces the size and thickness of leaf blade because branch pruning causes mulberry trees to lose an amount of nutrients accumulated in branches Moreover, according to Lin Shou Kang (1999), roots, hairs of mulberry trees temporarily die after branch pruning, then recover after a while Hence, the function of 20 nutrient in taking of roots is interrupted Whether roots' recovery time is fast or slow depends on pruning time and number of leaves left on stems 3.5.3 Effect of branch pruning on leaf yield Table 3.13 Productivity of experimental formulas Indicator Leaf yield (kg/100m2) Converted (ton) Time (date - month) - - 18 - 21 - 4- - 10 Total ab Pruning time 30.70 28.90 20.70 71.7 134.1 86.1 372.23 37.22 ab Pruning times 32.50 136.2 101.5 75.6 345.47 34.58 b Pruning times 31.90 128.3 114.4 57.4 332.03 33.20 a Leaf picking (control) 11.20 61.70 42.0 66.7 132.1 81.3 395.17 39.52 CV (%) 6.86 LSD0,05 49.52 Branch pruning thus reduces leaf yield by 6% to 16% compared to leaf picking, depending on the number of pruning time Based on the results of statistical analysis, leaf yield in single and double pruning formulas compared to leaf-picking are not significant, while double and triple punning formulas are significantly different in leaf yield with 95% reliability level The most effective method of harvesting mulberry leaves by branch pruning is to reduce labor in leaf picking and silkworm rearing stages To overcome the disadvantages of this technique, the density of mulberry plantation, cutting method and appropriate care need to be studyed 3.6 Study on the adaptation of GQ2 in some areas of Northern provinces of Vietnam 3.6.1 Testing on leaf yield We have planted GQ2 mulberry varieties in three localities: Moc Chau (Son La), located in the northern mountainous area, Thieu Do commune (Thanh Hoa Province), located in the northern central region and Tinh Cuong Commune, Cam Khe District (Phu Tho) belonging to the Red River Delta GQ2 has the number of leaves per meter of branch in trial locations smaller than the control variety, is it has longer node, while its leaf length and width are bigger Therefore, the leaf amount per meter of branch is also higher than the control variety This result is consistent with the comments in the comparative experiments above Table 3.14 Some indicators on leaves (Average in 2015) Unit: leaf, gam, cm Number of P leaves/m Leaf dimensions (cm) leaves/m Variety Location branch Length Width branch Thanh Hoa 24.80 60.70 18,40±0,70 15,40±0,40 Phu Tho 25.60 65.59 21,10±0,60 18,70±0,25 GQ2 Moc Chau 26.870 63.20 20,30±0,40 16,80±0,30 Average 25.70 63.20 19,93±0,50 16,60±0,30 Thanh Hoa 26.70 54.70 16,50±0,40 14,30±0,40 Phu Tho 26.90 57.80 18,70±0,30 15,60±0,60 VH13(control) Moc Chau 28.20 58.40 17,80±0,20 15,80±0,30 Average 27.30 56.96 17,60±0,30 15,10±0,40 21 Table 3.15 Leaf yield of GQ2 in testing locations Leaf yield (tons/ha) Location Variety 2014 2015 Average Unit: ton/ha % compared to breed 113,60 GQ2 37,06 38,20 37,60 VH13(control) 32,40 33,87 33,10 GQ2 39,74 40,80 40,30 119,20 Phu Tho VH13(control) 33,23 34,40 33,80 GQ2 33,80 35,90 34,80 112,90 Moc Chau VH13(control) 30,20 32,10 31,10 Although the three localities conducted variety testing have different soil fertility and climatic conditions, the leaf yield of GQ2 is higher than that of VH13 In Thanh Hoa, the average number of GQ2 variety exceeds 13%, Phu Tho with 19.20% and Moc Chau (Son La) with 12.90% On average, the yield of mulberry leaves GQ2 is 15% higher than that of the control variety Table 3.16 Infection degree of phyllactinia moricola, rust and virus Unit: % Phyllactinia Rust moricola Variety Characteristics Virus Rate Indicator Rate Indicator Thanh Hoa 20.40 4.85 6.10 3.10 10.77 Phu Tho 24.90 6.80 7.70 3.50 9.32 GQ2 Moc Chau 40.10 8.40 8.90 4.30 11.20 Average 28.46 6.70 7.60 3.63 9.08 Thanh Hoa 26.30 3.10 4.70 2.40 14.32 Phu Tho 18.90 4.20 5.30 2.50 10.22 VH13(control) Moc Chau 27.80 5.40 6.40 3.20 12.21 Average 21.00 4.20 5.46 2.70 12.25 Data obtained on infection level in the three locations show that the GQ2 has higher rate and indicator of disease in all three localities than VH13 in terms of Phyllactinia moricola Particularly in Moc Chau, the rate of disease is really high (40.10%) since the climate here has suitable temperature and humidity for the development of fungal diseases from May to September This data show that if the extension of GQ2 growing is conducted in Moc Chau, the application of measures to prevent Phyllactinia moricola disease is needed For rust disease, the difference between the two varieties is not large For viral disease, VH13 has higher disease rate than GQ2 3.6.2 Evaluation of leaf yield's stability of GQ2 The new high-yield mulberry varieties are a target of breeding, but at the same time new varieties need to be stabilized in terms of leaf yield during different crops and ecological regions Mulberry is a perennial crop that lasts 20-30 years, so the stability of leaf yield will contribute to the high economic efficiency of the mulberry industry Based on the results obtained on leaf yield of the new mulberry variety- GQ2, in each Thanh Hoa 22 crop of the year, in each year and in three trial locations, we affirm that the adaptability and stability of leaf yield are as follows: Table 3.17 Indicators of adaptation and stability of leaf yield of GQ2 through crops in Thanh Hoa, Phu Tho, Moc Chau Indicators Average Regression Indicator Reliability of Crop Variety productivity coefficient Ttn of level S2di stability (ton/ha) (bi) adaptation (P) (S2di) 11.11 0.523 0.915 0.007 1.066 0.617 GQ2 Spring VH13(control) 10.387 1.477 0.915 0.007 1.066 0.617 16.761 0.829 0.783 0.178 1.807 0.919 GQ2 Summer VH13(control) 14.471 1.171 0.783 0.178 1.807 0.919 9.76 0.989 0.057 -0.028 0.820 0.428 GQ2 Autumn VH13(control) 9.153 1.011 0.057 -0.028 0.820 0.428 The variety has a stable regression coefficient (bi), the indicator of adaptation is and the stability indicator S2di is The data in table 3.64 show that GQ2 has the regression coefficients (bi)  and the stability indicator (S2di)  but they are not significant Thus, GQ2 variety is determined to have high leaf yield, stable in spring, summer and autumn crops in the Red River Delta CONCLUSION AND PROPOSALS Conclusion 1.1 Results of the evaluation research on some mulberry varieties used as starting materials In the beginning of the crossbreeding, imported mulberry varieties from Guangdong and Guangxi China all had outstanding advantages such as early spring germination, number of germs and number of effective germs The size of leaf blade is large, the average leaf length and width of the varieties are higher than the local variety Ha Bac, with an increase of 8-32% and 5-27% respectively The IA variety of India is equivalent to Ha Bac mulberry variety The average leaf yield of varieties imported from Guangdong, Guangxi, China is 12-20% higher than that of Ha Bac variety, and only 5% higher than the IA variety of India Based on the results of the study, we have combined parent breeds for crossbreeding to create 10 cross combinations 1.2 Using crossbreeding to combine hydrid pairs between seven mulberry varieties of female flowers and six mulberry varieties of male flowers to create 10 cross combinations of VH18, VH19, VH20, VH21, VH22, VH23, VH24, VH25, GQ1 and GQ2 23 1.3 Making a comparison based on the results of 10 new cross combinations, we have selected four promising cross combinations that are VH19, VH20, GQ1 and GQ2 The annual yield of these cross combinations ranges from 33.20 tons to 36.47 tons per The leaf yield of the control variety VH13 is 31.74 tons Thus, compared to VH13, the leaf yield of these promising cross combinations increases from to 14.89% The regeneration characteristics of the mulberry trees after branch pruning of these are also better 1.4 Based on the results of the basic test on promising cross combinationsVH19, VH20, GQ1 and GQ2, we have selected GQ2 because of the following advantages: - GQ2 germinates earlier than VH13 from 13 to 15 days, the number of germs and effective germs increases from 35 to 36% - GQ2 has the total length of branches reaching 1996.83 cm, 12% higher than that of VH13 due to strong growth and germination in various crops, - The size of leaf blade is large, the average leaf length is 18.98 cm and the width is 15.93 cm, compared to 13% and 8% of the control variety respectively The leaf amount per meter of branch also increase by 16% - The average yield of leaves in years of GQ2 is 37.52 tons, exceeding VH13's yield by 15.74% - The leaf quality through the result of silkworm rearing in all spring, summer and autumn crops provides results of yield and cocoon quality that are not significantly different from VH13 - GQ2 has good regeneration ability After branch pruning, the growth rate of branches and leaves is faster, if branch pruning is conducted too many times, leaf blade becomes small and thin, the leaf yield drops - GQ2 is less susceptible and infected with stem-eating pests and virus disease but the rate and indicator of phyllactinia moricola are higher than that of VH13 The Scientific Council of the Ministry of Agriculture and Rural Development has approved the trial production of GQ2 mulberry variety in Northern provinces under Decision No 381 / QD-TT-CCN dated 23/08/2013 1.5 Results of the trial testing of GQ2 in some Northern provinces such as Thanh Hoa, Phu Tho and Moc Chau show that: - The average leaf yield of GQ2 in years in provinces-Thanh Hoa, Phu Tho and Moc Chau is 37.60 tons per ha, 15% higher than that of VH13 - Evaluation on the adaptability and stability of GQ2 in three trial locations shows that the adaptation indiator = and S2di = 0, proving that GQ2 has high leaf yield, and is stable and adapted to conditions of the trial localities Proposals It is necessary to continue studying and determining some appropriate technical measures to apply the method of harvesting mulberry leaves by branch pruning in order to reduce labor in harvesting mulberry and silkworm rearing 24 THE PUBLISHED ARTICLES IN RELATION TO THESIS Nguyen Thi Min (2010), "Research on selection of F1 hybrid seedlings", Journal of Agricultural Science and Technology of Vietnam, No (17) / 2010, pp 100-105 Nguyen Thi Min, Nguyen Van Thuc, Ha Van Phuc (2014) "Research results, breeding hybrid GQ2 hybrid for the North and Central provinces", Journal of Agricultural Science and Technology of Vietnam, No (48) / 2014, pp 63-72 Nguyen Thi Min, Nguyen Thi Luong, Nguyen Thi Thu Hang (2016), "Study on the effect of harvesting mulberry leaf by cuttings on growth in mulberry GQ2", Journal of Agricultural Science and Technology of Vietnam, No 11 (72) / 2016, pp 81-87 ... well adapted to the Central Highlands such as Lam Dong According to the report of Lam Dong Son Lam Agricultural Experiment Center (Phan Dinh Son et al., 1995), (Le Quy Tuyen - PhD in agriculture,... Furthermore, the labor used in harvesting mulberry and silkworm is growing, so the value is getting lower Over the past years, Vietnamese scientists have chosen to crossbreed and plant some new... "After more than 4,000 years of existence, silk has been the only fiber of intermittent length Since the beginning of time, silk does not depend on any artificial energy industry, nor does it produce