Identification of Productive Mulberry Silkworm Hybrids Resistant to Densonucleosis Virus Type 1 (BmDNV1)

Rao, P. Sudhakara,Nataraju B.,Balavenkatasubbaiah M.,Dandin S.B. Korean Society of Sericultural Science 2006 International Journal of Industrial Entomology Vol.13 No.2

The use of commercial silkworm hybrids resistant to important silkworm diseases is economical and better option particularly in tropical areas. This necessitated the evolution of productive bivoltine silkworm breeds non-susceptible to $BmDNV_1$. Non-susceptibility to $BmDNV_1$, infection was found to be controlled by a single recessive gene, nsd-l or a dominant gene, Nid-l. A major dominant/recessive gene confers resistance to $BmDNV_1$, from potent donor parents have been transferred to 10 productive but susceptible bivoltine silkworm strains through conventional breeding methods. By utilizing these breeds prepared 25 hybrids $(5{\times}5)$ and hybrid evaluation was carried out to identify most promising hybrids resistant to $BmDNV_1$. All these hybrids are inoculated with $BmDNV_1$ inoculum along with productive control hybrid $CSR2{\times}CSR4$ and reared under standard rearing procedure. Based on inoculated rearing and test reeling results, two most promising hybrids $(CSR18DR{\times}CSR29DR\;and\;CSR21DR{\times}CSR50DR)$ were selected for commercial exploitation. The selected hybrids have shown a survival rate of >85% with productive traits, where as control hybrid have shown 11.1% survival with inferior cocoon traits. The methodologies adopted were discussed.

Estimation of Heterosis and Combining Ability in Hybrids between Resistant and Susceptible Bivoltine Breeds of Silkworm Bombyx mori to Densonucleosis Virus1 (BmDNV1)

Rao, P. Sudhakara,Nataraju B.,Balavenkatasubbaiah M.,Dandin S.B. Korean Society of Sericultural Science 2006 International Journal of Industrial Entomology Vol.13 No.2

Combining ability and hybrid vigour analysis was carried out in hybrids between newly developed non-susceptible lines to BmDNV1 and popular bivoltine breeds for certain quantitative traits viz. Pupation rate, Cocoon yield, Cocoon weight, Cocoon shell weight and Cocoon shell ratio, Survival rate against BmIFV and BmNPV. General combining ability (GCA) effects revealed that among the lines CSR2DR was found good general combiner exhibiting significant GCA effects for six characters, out of seven traits evaluated. Among testers CSR28DR was found as good combiner exhibiting significant GCA effects for six traits. Out of 36 hybrids made between $resistant{\times}resistant,\;resistant{\times}susceptible\;and\;susceptible{\times}susceptible$ breeds, one hybrid $CSR21DR{\times}CSR28DR$ exhibited significant SCA effects for six traits. The selected hybrid $CSR21DR{\times}CSR28DR$ also exhibited significant positive heterosis and heterobeltiosis expressions for maximum traits and could be exploited as commercial silkworm hybrid resistant to important viral diseases.

Identification of Productive Mulberry Silkworm Hybrids Resistant to Densonucleosis Virus Type 1 (BmDNV1)

( P. Sudhakara Rao ),( B. Nataraju ),( M. Balavenkatasubbaiah ),( S. B. Dandin ) 한국잠사학회 2006 International Journal of Industrial Entomology Vol.13 No.2

The use of commercial silkworm hybrids resistant to important silkworm diseases is economical and better option particularly in tropical areas. This necessitated the evolution of productive bivoltine silkworm breeds non-susceptible to BmDNV1. Non-susceptibility to BmDNV1 infection was found to be controlled by a single recessive gene, nsd-l or a dominant gene, Nid-l. A major dominant/recessive gene confers resistance to BmDNV1 from potent donor parents have been transferred to 10 productive but susceptible bivoltine silkworm strains through conventional breeding methods. By utilizing these breeds prepared 25 hybrids (5 × 5) and hybrid evaluation was carried out to identify most promising hybrids resistant to BmDNV1. All these hybrids are inoculated with BmDNV1 inoculum along with productive control hybrid CSR2 × CSR 4 and reared under standard rearing procedure. Based on inoculated rearing and test reeling results, two most promising hybrids (CSR18DR × CSR29DR and CSR21DR × CSR50DR) were selected for commercial exploitation. The selected hybrids have shown a survival rate of >85% with productive traits, where as control hybrid have shown 11.1 % survival with inferior cocoon traits. The methodologies adopted were discussed.

Estimation of Heterosis and Combining Ability in Hybrids between Resistant and Susceptible Bivoltine Breeds of Silkworm Bombyx mori to Densonucleosis Virus1 (BmDNV1)

( P. Sudhakara Rao ),( B. Nataraju ),( M. Balavenkatasubbaiah ),( S. B. Dandin ) 한국잠사학회 2006 International Journal of Industrial Entomology Vol.13 No.2

Combining ability and hybrid vigour analysis was carried out in hybrids between newly developed non-susceptible lines to BmDNV1 and popular bivoltine breeds for certain quantitative traits viz. Pupation rate, Cocoon yield, Cocoon weight, Cocoon shell weight and Cocoon shell ratio, Survival rate against BmIFV and BmNPV. General combining ability (GCA) effects revealed that among the lines CSR2DR was found good general combiner exhibiting significant GCA effects for six characters, out of seven traits evaluated. Among testers CSR28DR was found as good combiner exhibiting significant GCA effects for six traits. Out of 36 hybrids made between resistant × resistant, resistant × susceptible and susceptible × susceptible breeds, one hybrid CSR21DR × CSR28DR exhibited significant SCA effects for six traits. The selected hybrid CSR21DR × CSR28DR also exhibited significant positive heterosis and heterobeltiosis expressions for maximum traits and could be exploited as commercial silkworm hybrid resistant to important viral diseases.

Hybrid Vigour in Polyvoltine $\times$ Bivoltine (Sex-Limited Cocoon Colour) Hybrids of Silkworm Bombyx mori L.

Rao, P.Sudhakara,Rekha, M.,Naik, V.Nishitha,Pallavi, S.N.,Mahalingappa, K.C. Korean Society of Sericultural Science 2002 International Journal of Industrial Entomology Vol.4 No.1

Heterosis studies on rearing performance of 25 Fl Polyvoltine $\times$ bivoltine (sex-limited cocoon colour) hybrids revealed that manifestation of heterosis was highly significant for majority of the economic traits contributing to more silk yield. Five hybrids namely BL24${\times}$ CSR 19 (SL), BL24${\times}$</TEXB72 (SL), B167${\times}$</TEX05R19 (SL), BL67${\times}$</TEXB72 (SL)and96A${\times}$</TEXB72 (SL)were highly promisins over the popular hybrid PM ${\times}$</TEX NB4D2.These five hybrids exhibited significant heterosis and heterobeltiosis for most of the traits studied and can be commercially exploited by taking genetic advantage of sexlimited cocoon colour bivoltine breeds on economic lines.

Evolution of a Productive Bivoltine Hybrid of Silkworm Bombyx mori L. (SD7×SD12) with Shorter Larval Duration

( P. Sudhakara Rao ),( H. K. Basavaraja ),( G. V. Kalpana ),( V. Nishitha Naik ),( K. C. Mahalingappa ),( S. N. Pallavi ) 한국잠사학회 2007 International Journal of Industrial Entomology Vol.8 No.1

With an objective of evolving quantitatively and qualitatively superior bivolitine silkworm hybrid of Bombyx mori L. for tropics with shorter larval duration without compromising on productivity traits, a breeding programme was initiated at this institute during 1997 by utilizing breeding resource material from the institutes Germplasm collection. The breed SD7 is characterized with plain larvae spinning white oval cocoons and SD12 is characterized by sex-limited larval markings spinning white dumb-bell cocoons. After fixation, these breeds along with other newly evolved breeds were subjected for hybrid evaluation in the laboratory. Based on the hybrid studies, the hybrid SD7×SD12 was selected and evaluated for one year comprising three major seasons (6 trials) of tropics viz., Pre-monsoon (characterized by high temperature, low humidity and without any rain fall), Monsoon (characterized by moderate temperature, heavy rain fall with high humidity) and post-monsoon season (characterized by low temperature and low humidity with frequent rain fall) to know the fluctuations in the larval duration. The evaluation studies indicated that the hybrid is having shorter larval duration with productive merits. The hybrid SD7×SD12 recorded survival percent of 92.74, shell weight of 46.7 cg, shell ratio % of 24.0 and filament length of 1,200 meters with a shorter larval duration of 24 hrs; when compared to productive hybrid CSR2×CSR5 (control). The breeding methodologies and hybrids usefulness for tropics were discussed.

Note : Line×Tester Analysis of Certain Quantitative Traits in Silkworm Bombyx mori L. under Optimum and Stress Rearing Conditions

( P. Sudhakara Rao ),( R. K. Datta ),( K. M. Vijaya Kumari ),( A. K. Palit ),( S. A. Bhat ) 한국잠사학회 2007 International Journal of Industrial Entomology Vol.8 No.1

The combining abilities in the 5 newly evolved thermo tolerant breeds viz., SR6, SR7, SR8 SR9 and SR10 of silkworm Bombyx mori L. and their 15 hybrids were made in a line×tester crossing programme. Data were analysed for seven quantitative traits i.e., pupation rate, cocoon yield, cocoon weight, cocoon shell weight, cocoon shell ratio, filament length and raw silk percentage under optimum room temperature (25±1℃) conditions (In case of high temperature (36±1℃) stress conditions five economic traits except filament length and raw silk percentage) with 3 widely adapted testers i.e., KA, CSR2 and CC1 as lines (females) and testers (males) respectively. The performance at high temperature and low humidity conditions are only taken into consideration for selecting the best lines/hybrids. Among the lines SR6 exhibited positive General combining ability (GCA) effects for pupation rate, cocoon yield, cocoon weight and cocoon shell ratio traits, followed by SR7 for pupation rate, cocoon yield and cocoon shell weight and cocoon shell ratio. Among testers, KA exhibited positive GCA effects for two quantitative traits cocoon yield, cocoon weight and CSR2 for cocoon shell weight and cocoon shell ratio under adverse temperature conditions. The hybrid SR6×CC1 and SR7×CSR2 exhibited significant positive Specific combining ability (SCA) effects for majority of the traits in high temperature stress conditions of rearing. The better parent value of heterosis (Heterobeltiosis) was exhibited by the hybrid SR6×CC1 for pupation rate, cocoon yield, cocoon weight and cocoon shell weight and SR7×CSR2 for all the traits evaluated under high temperature conditions. Based on the results, the lines SR6 and SR7 was judged as best combiners and the hybrids SR6×CC1 and SR7×CSR2 can be selected for commercial exploitation in tropical climate.

Heterotic Expression in Silk Productivity of Newly Evolved Thermo-tolerant Bivoltine Hybrids of Silkworm Bombyx mori L.

Rao, P.Sudhakara,Datta, R.K.,Vijaya Kumari, K.M.,Palit, A.K.,Haque Rufaie, S.Z. Korean Society of Sericultural Science 2004 International Journal of Industrial Entomology Vol.9 No.1

Studies on heterotic expression in the silk productivity of 66 thermo-tolerant bivoltine hybrids reared under high temperature $(36{\times}1^{\circ}C)$ and low humidity (60${\times}$5%) conditions revealed that manifestation of heterosis was highly significant for majority of the quantitative traits contributing to more cocoon productivity. Observations were made on 8 economically important traits such as fecundity, pupation rate, cocoon yield, cocoon weight, cocoon shell weight, cocoon shell ratio, cocoon filament length and raw silk. Analysis of variance results revealed great deal of variability indicating significant (P < 0.001) variations. Out of 66 hybrids, 7 hybrids exhibited positive heterosis for seven traits and 4 hybrids expressed significant hetero-beltiosis for 6 traits, out of 8 traits evaluated. Based on results, the hybrids ${SR_1} {\times} {SR_5}and {CSR_2} {\times} {SR_5}$ are adjudged as most promising ones and can be exploited commercially in tropical climates to increase the cocoon productivity.

Evolution of a Productive Bivoltine Hybrid of Silkworm Bombyx mori L. (SD7 x SD12) with Shorter Larval duration

P. Sudhakara Rao,H. K. Basavaraja,G. V. Kalpana,V. Nishitha Naik,K. C. Mahalingappa,S. N. Pallavi 한국잠사학회 2004 International Journal of Industrial Entomology Vol.8 No.1

With an objective of evolving quantitatively and qualitatively superior bivoltine silkworm hybrid of Bombyx mori L. for tropics with shorter larval duration without compromising on productivity traits, a breeding programme was initiated at this institute during 1997 by utilizing breeding resource material from the institutes Germplasm collection. The breed SD7 is characterized with plain larvae spinning white oval cocoons and SD12 is characterized by sex-limited larval markings spinning white dumb-bell cocoons. After fixation, these breeds along with other newly evolved breeds were subjected for hybrid evaluation in the laboratory. Based on the hybrid studies, the hybrid SD7 ´ SD12 was selected and evaluated for one year comprising three major seasons (6 trials) of tropics viz., Pre-monsoon (characterized by high temperature, low humidity and without any rain fall), Monsoon (characterized by moderate temperature, heavy rain fall with high humidity) and post-monsoon season (characterized by low temperature and low humidity with frequent rain fall) to know the fluctuations in the larval duration. The evaluation studies indicated that the hybrid is having shorter larval duration with productive merits. The hybrid SD7 ´ SD12 recorded survival percent of 92.74, shell weight of 46.7 cg, shell ratio % of 24.0 and filament length of 1,200 meters with a shorter larval duration of 24 hrs; when compared to productive hybrid CSR2 ´ CSR5 (control). The breeding methodologies and hybrids usefulness for tropics were discussed.

Line × Tester Analysis of Certain Quantitative Traits in Silkworm Bombyx mori L. under Optimum and Stress Rearing Conditions

P. Sudhakara Rao,R. K. Datta,K. M. Vijaya Kumari,A. K. Palit,S. A. Bhat 한국잠사학회 2004 International Journal of Industrial Entomology Vol.8 No.1

The combining abilities in the 5 newly evolved thermo tolerant breeds viz., SR6, SR7, SR8 SR9 and SR10 of silkworm Bombyx mori L. and their 15 hybrids were made in a line ´ tester crossing programme. Data were analysed for seven quantitative traits i.e., pupation rate, cocoon yield, cocoon weight, cocoon shell weight, cocoon shell ratio, filament length and raw silk percentage under optimum room temperature (25 ± 1oC) conditions (In case of high temperature (36 ± 1oC) stress conditions five economic traits except filament length and raw silk percentage) with 3 widely adapted testers i.e., KA, CSR2 and CC1 as lines (females) and testers (males) respectively. The performance at high temperature and low humidity conditions are only taken into consideration for selecting the best lines/ hybrids. Among the lines SR6 exhibited positive General combining ability (GCA) effects for pupation rate, cocoon yield, cocoon weight and cocoon shell ratio traits, followed by SR7 for pupation rate, cocoon yield and cocoon shell weight and cocoon shell ratio. Among testers, KA exhibited positive GCA effects for two quantitative traits cocoon yield, cocoon weight and CSR2 for cocoon shell weight and cocoon shell ratio under adverse temperature conditions. The hybrid SR6 ´ CC1 and SR7 ´ CSR2 exhibited significant positive Specific combining ability (SCA) effects for majority of the traits in high temperature stress conditions of rearing. The better parent value of heterosis (Heterobeltiosis) was exhibited by the hybrid SR6 ´ CC1 for pupation rate, cocoon yield, cocoon weight and cocoon shell weight and SR7 × CSR2 for all the traits evaluated under high temperature conditions. Based on the results, the lines SR6 and SR7 was judged as best combiners and the hybrids SR6 ´ CC1 and SR7 ´ CSR2 can be selected