Boil-off loss ratio is one of the most important economic traits to be considered during the course of silkworm breeding. The boil-off loss ratio varies among the breeds and seasons.The present study was undertaken with 5 oval and 5 peanut breeds and twenty five hybrids involving these parents to select the promising hybrids with desired boil-off loss ratio. Accordingly, studies were undertaken to estimate the heterosis and heterobeltiosis. It was observed that majority of the hybrids revealed negative heterosis for boil-off loss ratio which is desirable. Based on the heterosis and heterobeltiosis, among all the hybrids, the hybrid APBRO5 x APBRD5 exhibited highest negative heterosis for boil-off loss ratio and also exhibited highest EI value (64.5) for the quantitative and qualitative traits. Based on the hybrids performance, boil-off loss ratio, heterosis and heterobeltiosis and evaluation index, the hybrids viz. APBRO5 x APBRD5, APBRO1 x APBRD1 and APBRO3 x APBRD4 were identified for commercial exploitation. IntroductionTo face the global competitiveness in silk production there is a need to improve the quality of the raw silk and as such the sericulture industry requires good quality of silk to produce internationally gradable silk fabric to meet the requirement of the consumers across the world resulting in increased foreign exchange. To meet the specific requirement of the silk industry, the silkworm breeders have developed various hybrids such as productive breeds, robust breeds, breeds with special traits and sex limited races etc. Keeping this in view, most of the silkworm breeders have been concentrating on boil-off loss ratio to produce good quality silk as the boil-off loss ratio is one of the most important qualitative trait in silkworm breeding. The silkworm Bombyx mori L. spins a shell by extruding silk bave at the end of its larval period. The silk bave is composed of two silk proteins namely fibroin and sericin and also contains a small quantity of fatty, waxy, colouring and mineral matters. The fibroin protein occupies the middle portion of the Boil-off loss ratio in newly developed bivoltine silkworm hybrids 14 separation and assessment, 60 cocoon shells (30 each of female and male) were selected from each breed/ hybrid separately. Three replications were maintained each having 10 males and 10 females for conducting the experiment. Degumming was carried out by boiling the cocoon shells in soap solution using a standard procedure (Basavaraja et al., 2000). Two step boiling method as explained below was employed for the degumming of the cocoon shells and used neutral liquid soap for boiling. A quantity of 7g soap was dissolved in 1 liter of water for degumming and the material: liquor ratio was maintained as 1:40. First degummingThe liquor solution of the soap and soda was boiled in a copper vessel. When the boiling media solution reached the boiling point (>90 o C), the cocoon shell sample bags were immersed completely in boiling media kept tightly closed for 40 minutes. At an interval of 10 m...
To meet the local requirement i.e. the tropical stress of Andhra Pradesh and marginal farmers, twenty four new hybrid combinations were tested in Line x Tester method involving eight newly developed polyvoltine oval lines viz., MSO1, MSO2, MSO3, MSO4, MSO5, MSO6, MSO7 and MSO8 and three bivoltine silkworm breeds viz., APS12, APS45 and APS8 as testers. These hybrids were reared to evaluate their performance. Data for eight economically important metric traits viz., fecundity, cocoon yield per 10,000 larvae by number, cocoon yield per 10,000 larvae by weight, survival rate, cocoon weight, cocoon shell weight, cocoon shell ratio and filament length was recorded. General combining ability (gca), specific combining ability (sca) and heterosis were analyzed. Further, the relative merit of the hybrids for all the traits under study was also assessed adopting Evaluation Index method. Based on combining ability effects, heterosis and evaluation index, five hybrid combinations viz., MSO3 x APS45, MSO1 x APS12, MSO7 x APS8, MSO2 x APS45 and MSO1 x APS45 were selected for further evaluation in different seasons.
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