• International Journal of Industrial Entomology and Biomaterials
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• v.13 no.2
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• pp.109-112
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• 2006

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.

• International Journal of Industrial Entomology and Biomaterials
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• v.12 no.2
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• pp.95-100
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• 2006

Central Sericultural Research and Training Institute, Mysore have evolved several highly productive bivoltine hybrids which can produce international grade raw silk. Among them $CSR2{\times}CSR4,\;CSR2{\times}CSR5,\;CSR3{\times}CSR6,\;CSR17{\times}CSR16,\;CSR18{\times}CSR19$ and $CSR12{\times}CSR6$ are being popularized in the field. There is a minimum difference in their economic characters but they appear to differ in survival. Though they are productive under high input management conditions, they are very susceptible to different diseases under normal rearing practices. No systematic attempts have been made to test their susceptibility status / resistance. Thus the present study is a modest attempt to screen the above six productive bivoltine hybrids to two important pathogens viz., Bombyx mori Nuclear Polyhedrosis Virus (BmNPV) and Bombyx mori Infectious Flacherie Virus (BmIFV) along with existing hybrid, $KA{\times}NB4D2$ to assess their susceptibility / resistance. The results shows that the productive hybrid $CSR2{\times}CSR4$ is the most resistant to BmNPV and it is suggested by its highest $LC_{50}$ value followed by $CSR12{\times}CSR6,\;KA{\times}NB4D2,\;CSR3{\times}CSR6,\;CSR17{\times}CSR16,\;CSR18{\times}CSR19,\;CSR2{\times}CSR5$. Based on the $LC_{50}$ value and $LT_{50}$ values for BmIFV, the hybrid $KA{\times}NB4D2$ was found to be the most resistant (1st position) one followed by $CSR3{\times}CSR6$ (2nd position) $CSR2{\times}CSR$ (3rd position) and $CSR12{\times}CSR6$ (4th position) $CSR17{\times}CSR16$, $CSR18{\times}CSR19$ (5th position) and $CSR2{\times}CSR5$ being the least. The response of 7 bivoltine hybrids to both the pathogens BmNPV and BmIFV indicates that, the hybrids $CSR2{\times}CSR4$, $CSR12{\times}CSR6$ and $KA{\times}NB4D2$ were found to be the most resistant when compared to others. Further, $KA{\times}NB4D2$ being less productive hybrid with a shell ratio of 20.08%, the other two hybrids $CSR2{\times}CSR4$ (Cocoon shell ratio, 21.44%) and $CSR12{\times}CSR6$ (cocoon shell ratio, 23.45%) can be considered to be most productive with superior quality cocoon and resistant to both BmNPV and BmIFV pathogens. The overall study indicated that the hybrid $CSR2{\times}CSR5$ is the most susceptible hybrid to both the pathogens.

• International Journal of Industrial Entomology and Biomaterials
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• v.14 no.1
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• pp.15-21
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• 2007

Three newly authorized bivoltine silkworm hybrids namely, $CSR2{\times}CSR4$ (productive single hybrid), $(CSR6{\times}CSR26){\times}(CSR2{\times}CSR27)$ (productive double hybrid) and $CSR18{\times}CSR19$ (robust single hybrid) were chosen for the present study. These hybrids were subjected to different temperature and humidity treatments i.e., $25{\pm}$1^{\circ}C and RH $65{\pm}5%$ (control), $30{\pm}1^{\circ}C$, with combinations of low relative humidity (RH $65{\pm}5%$) and high RH ($85{\pm}5%$) at different stages during rearing and spinning of silkworm larvae. The larvae of after 3rd moult were subjected to different thermal and humidity stress till the assessment of cocoon traits. The comparative rearing and reeling performance clearly indicated that the deleterious effect of high temperature and high RH was more pronounced for the majority of traits such as cocoon uniformity, cocoon weight, shell weight, shell percentage, reelability, filament length, raw silk percentage raw silk recovery denier and waste percentage on silk weight than other temperature and RH treatments and this effect was almost similar for all three silkworm hybrids studied. The present investigation clearly indicate that the deleterious effect of high temperature and high RH was more pronounced on rearing and spinning of silkworm larvae than other temperature and RH treatments and similar effect was noticed for all the three silkworm hybrids studied. The cocoon characters can be improved by providing ideal environmental conditions even during spinning stage of larvae affected with high temperature and RH. The study also suggest that high temperature and low humidity has greater effect during rearing stage than spinning stage.

• International Journal of Industrial Entomology and Biomaterials
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• v.7 no.2
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• pp.209-219
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• 2003

An experiment was initiated to evaluate hybrid vigour in twelve F$_1$ hybrids and seven three-way crosses of multivoltine ${\times}$ bivoltine silkworm between newly evolved multivoltine breed BL67 with productive bivoltine CSR breeds and hybrids. Analysis of variances computed for different characters among F$_1$hybrids and three-way crosses showed highly significant differences among them indicating presence of both additive and non-additive gene actions for the expression of these characters. Among twelve F$_1$ hybrids, two F$_1$ hybrids viz., BL67${\times}$CSR$_4$and BL67${\times}$CSR$_{5}$ have expressed significant heterosis for nine characters and two hybrids viz., BL67${\times}$NB$_4$D$_2$and PM${\times}$NB$_4$D$_2$ for eight characters whereas out of nine three-way crosses, three hybrids viz., BL67${\times}$ (CSR$_3$${\times}$CSR$_{6}$), BL67${\times}$(CSR$_{16}$${\times}$CRS$_{17}$) and BL67${\times}$(CSR$_{18}$ ${\times}$CSR$_{19}$) expressed significant heterosis for eight characters. In the present study, it is observed that the cocoons of two hybrids viz., BL67${\times}$CSR$_4$and BL67${\times}$CSR$_{19}$ were found to be uniform as these hybrids showed lowest CV％ (5.35 and 5.38) among twelve F$_1$ hybrids and seven three way crosses between multivoltine ${\times}$ bivoltine hybrids. Four F$_1$ hybrids viz., BL67${\times}$CSR$_4$, BL67${\times}$CSR$_{5}$, BL67${\times}$ (CSR$_3$${\times}$CSR$_{6}$), BL67${\times}$(CSR$_{16}$${\times}$CRS$_{17}$) and BL67${\times}$(CSR$_{18}$ ${\times}$CSR$_{19}$) showed superiority in expressing hybrid vigour and are considered as best heterotic hybrids for commercial exploitation.ion.ation.ion.ation.ion.

• International Journal of Industrial Entomology and Biomaterials
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• v.11 no.1
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• pp.27-36
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• 2005

Successful silkworm breeding attempts were made at Andhra Pradesh State Sericulture Research and Development Institute (APSSRDI), Hindupur, India in developing productive bivoltine silkworm hybrids. One hundred hybrid combinations involving 10 parents (five each of oval and peanut) were evaluated in complete diallel pattern and identified the combination APS$_{83}$ $\times$ APS$_{102}$ as most promising. This hybrid showed economic merit for the characters fecundity (524 eggs/laying), pupation percentage (96.0$\%$), cocoon yield per 10,000 larvae by weight (19.0 kg), cocoon weight (1.85 g), shell weight (41.7 cg), shell ratio (22.5$\%$), filament length (1,004 m), reelability (88.4$\%$), raw silk recovery (18.4$\%$) and neatness (92 point) over the control hybrid APS$_{9}$ $\times$ APS$_{8}$ The breeding process and identification of APS$_{83}$ $\times$ APS$_{102}$ is discussed in the paper.

• International Journal of Industrial Entomology and Biomaterials
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• v.5 no.2
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• pp.153-162
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• 2002

Earlier breeding experiments undertaken at Central Sericultural Research and Training Institute, Mysore, India since a decade had resulted in the development of many productive and qualitatively superior bivoltine hybrids. However, the hot climatic conditions of tropics prevailing particularly in summer are not conducive to rear these high yielding bivoltine hybrids. This has necessitated breeding of compatible bivoltine hybrids for year-round rearing. Accordingly, the Japanese hybrid, B2Ol ${\times}$ BCS12 which was found to be tolerant to high temperature was used as breeding resource material. Following hybridization and selection rearing of silkworms was taken up in SERICATRON (Environmental chamber with precise and automatic control facilities for uniform maintenance of temperature and humidity) at high temperature of $36{\times}1^{\circ}C$ and 85${\times}$5% RH in fifth instar and the control batches at $25{\times}1^{\circ}C$ and 65{\times}$5% RH. Directional selection was resorted to the batches reared at 36$\pm$1$^{\circ}C$ till F$_{5}$ keeping pupation rate as important selection criteria. From $F_{2}% onwards the experiment was modified in such a way as to conduct normal rearing every alternate generation to regain the lost vitality due to continuous exposure to high temperature and high humidity stress. At $F_{2}$ , Oval and dumb-bell cocoons were separated out and designated as CSR18 and CSR19, respectively. By utilizing these lines at $F_{12}$, the hybrid CSR18$\times$CSR19 was prepared and studied for the thermotolerance by subjecting to stress condition at high temperature of 36$\pm$1$^{\circ}C$ and 85$\pm$5% RH in fifth instar and the control batches at $25{\times}1^{\circ}C$ and 65${\times}$5% RH. The better performance of CSR18${\times}$CSR19 (survival > 88%) at $36{\times}1^{\circ}C$ clearly indicates the general superiority of CSR18${\times}$CSR19 with regard to high temperature tolerance over the productive hybrids and CSR18$\times$CSR19 can perform well in varied agro-climatic conditions of the tropics with optimum qualitative and quantitative characteristics.s.

• International Journal of Industrial Entomology and Biomaterials
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• v.3 no.2
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• pp.127-133
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• 2001

With an objective of evolving quantitatively and qualitatively superior bivoltine breeds/hybrids of silkworm Bombyx mori L. for tropical conditions, breeding work was initiated in Central Sericultural Research and Training Institute, Mysore during 1992 by utilizing two Japanese hybrids namely BNl8$\times$BCS25 and Shunrei$\times$Shogetsu along with Indian evolved breed, KA. The breed CSR12 which is characterized with sex-limited larval marking and white oval cocoons was evolved from the Japanese hybrid BNl8 ${\times}$ BCS25 by crossing with KA, while the breed CSR6 which is characterized with normal marking (marked larvae) and white dumbbell cocoons was extracted from the Japanese commercial hybrid Shunrei${\times}$Shogetsu through continuous inbreeding coupled with selection. After fixation, these breeds along with other newly evolved breeds were subjected to hybrid study under optimum environmental conditions in the laboratory for expression of full potential of the genotypes. These hybrids were evaluated by Multiple Trait Evaluation Index (Mano et al., 1993). The hybrid CSR12${\times}$CSR6 was selected based multiple trait evaluation index value. The hybrid CSR12$\times$CSR6 recorded survival of 96.0%, shell weight of 50.0 cg, shell ratio of 24.3%, raw silk percentage of 19.6, filament length of 1,216 m, boil off loss of 22.4% and renditta of 5.1. On the other hand, the control hybrid (KA ${\times}$ NB4D2) has recorded survival of 90.6%, shell weight of 42.1 cg, shell ratio of 20.4%, raw silk percentage of 15.9, filament length of 999 m, boil off loss of 24.8% and renditta of 6.3. The hybrid CSR12$\times$CSR6 was authorized during 1997 by Central Silk Board, Government of India for commercial exploitation during favourable months based on national level race authorization test.

• International Journal of Industrial Entomology and Biomaterials
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• v.8 no.2
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• pp.129-133
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• 2004

The breeding work was initiated by utilizing two Japanese hybrids namely C135${\times}$N134 and N137${\times}$C146 along with two evolved Indian breeds, J14 and A24. The breed CSR16 which is characterized with marked larvae and white dumbbell cocoons was evolved from the Japanese hybrid C135${\times}$N134 by crossing with J14, while the breed CSR17 which is characterized with plain larvae and white oval cocoons was evolved from the Japanese hybrid N137${\times}$C146 by crossing with A24. The hybrid of these evolved breeds i.e., CSR16${\times}$CSR17 has shown superior over control hybrid $KA{\times}{NB_4}{D_2}$ and on par with the ruling hybrid of CSR2${\times}$CSR4. The hybrid CSR16${\times}$CSR17 was authorized during 1999 by Central Silk Board, Bangalore, Government of India for commercial exploitation during favourable months based on national level race authorization test.

• International Journal of Industrial Entomology and Biomaterials
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• v.4 no.2
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• pp.121-126
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• 2002

Breeding programme was initiated during November, 1995 with the main objective to breed productive multivoltine breeds/ hybrids with suitable genetic constitution to suit the fluctuating tropical climate prevailed in India. Two multivoltine breeds viz., BL-24 and BL-27 selected were as breeding resource materials from the silkworm germplasm maintained at Central Sericul-tural Research and Training Institute, Mysore. By adopting hybridization, backcrossing inbreeding and selection, a new multivoltine breed namely BL-67. This breed spins light greenish yellow cocoons and cocoon shape is oval with medium to coarse grains. The evolved breed was crossed with five tropical bivoltine breeds viz., NB4D2, CSR2, CSR5, CSR18 and CSR101 to study the combining ability, and identified a superior hybrid, BL67 ${\times}$ CSR101, named as CAUVERY, The hybrid is characterized by high pupation rate (>95%), high shell weight (> 35 cg), high cocoon shell ratio (> 20%), longer filament length (> 900 m) and high neatness (93) with a renditta of 6.5 producing 2A-3A grade silk. The hybrid is selected for Race Autho-rization test of Central Silk Board.

• International Journal of Industrial Entomology and Biomaterials
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• v.10 no.2
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• pp.147-151
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• 2005

Serious attempt for the improvement of quality parameters in silkworm hybrids came rather very late in India. Realising the need for productive breeds to the field and reorientation in breeding methodology, the silkworm breeders of CSRTI, Mysore were able to develop silkworm breeds with fine denier namely, JPN7, CSR48, B63 and B65 of specific industrial requirement through directional selection. As the success of silkworm breeds mainly depends on their combining ability, the developed breeds were subjected for hybrid evaluation. Out of 42 bivoltine hybrids studied, one hybrid, $CSR48{\times}CSR5$ was identified for its superiority over the existing bivoltine hybrids namely $CSR2{\times}CSR4,\;CSR2{\times}CSR5\;and\;CSR18{\times}CSR19$ for majority of qualitative traits. Post cocoon testing of large quantity of cocoons of $CSR48{\times}CSR5$ resulted in the production of high quality '3A'grade silk. It is for the first time in the Indian Sericulture industry that high quality silk with longer filament length of 1474 m, denier of 2.47, standard size deviation of 0.983 d, maximum size deviation of 1.322, neatness of 96 p, reelability of $85\%$, tenacity of 3.87 g/d, elongation of $22.32\%$ and cohesion of 110 strokes was produced. The superiority of fine denier silkworm breeds and their hybrids are discussed.