15    International Journal of Advanced Science and Research ISSN: 2455-4227, Impact Factor: RJIF 5.12 www.newresearchjournal.com/science Volume 1; Issue 3; March 2016; Page No. 15-20 Comparative performance and differential expression of economic parameters in the parents of bivoltine silkworm, Bombyx mori L. and their hybrids 1 Veeranna Gowda, 2 Kalpana GV, 3 Ashok Kumar K 1, 3 Central Sericultural Germplasm Resources Centre, Hosur, Tamil Nadu, India 2 P4 Basic Seed Farm, Hassan, Karnataka, India Abstract Comparative performance of selected parental and different crossing pattern hybrids is an important yard stick to understand the potentiality of a breed / hybrid for evaluating the differential expression of quantitative traits. The parental breeds, foundation crosses and different cross hybrids were reared in three replications during three different seasons of the year to evaluate their performance for pre- and post-cocoon traits. Hybrid vigor in terms of heterosis for different crossing pattern hybrids was studied for important economic traits. The results of the study reveals that, out of different crossing pattern hybrids studied, two each of single, three-way and four-way cross hybrids exhibited better performance with desirable positive heterosis for most of the economic traits, which may be attributed to better inherent advancement and prophecy for field testing based on the overall performance and heterosis for each of the quantitative trait studied. Keywords: - Quantitative traits, bivoltine silkworm, crossing pattern, estimation, hybrid vigour.  Introduction The bivoltine silkworm breeds / hybrids that are currently being exploited in the field are developed through suitable breeding approach by utilizing Japanese hybrids has resulted in development of many productive bivoltine breeds (Datta et al., 2000; Basavaraja et al., 1995). For assessing the productivity and their suitability to confined environment, the breeds / hybrids are to be subjected to favorable and unfavorable conditions. Genotype and environmental interactions is of major importance in breeding to develop new breeds as it is well established that the phenotypic expression of the genotype for different traits are not consistent in all the environmental conditions. Further, the diverse environmental factors prevailing in the tropics, management practices and quality of leaf plays a significant role in the expression of quantitative traits. Hybrid vigour in silkworm has received a considerable attention because of the marked effect of the important economic parameters including the yield components. As per the literature, it is documented that the single cross hybrids are superior to their parents in many qualitative as well as quantitative characters. The superiority of the hybrids is adjudicated by their cocoon yield and yield attributes as compared to their parents. In India, utilization of hybrid vigor came rather belatedly and maximum utilization was undoubtedly contributed by the crosses of multivoltine with bivoltine inbred lines. Since last two decades, relatively good number of potential bivoltine breeds / hybrids were identified (Basavaraja et al., 1995; Nirmal Kumar et al., 1998; Mal Reddy et al., 2005) and the quantitative traits of some of these identified breeds / hybrids were documented (Datta et al., 2000). However, information on hybrid vigor in different crossing pattern of these bivoltine breeds is scanty. Hence, an attempt has been made to analyze the comparative performance of bivoltine parental as well as foundation crosses (FC) and single, three-way and four-way crosses in three replications during different seasons of the year. Also, analyzed evaluation of differential expression of heterosis in different crossing pattern viz., foundation, single, three-way and four- way cross hybrids involving identified promising bivoltine parental breeds. Materials and Methods Twelve bivoltine breeds viz., BBE226, CSR27, CSR17, JPN8, JPN7, S5 (oval) and BBE267, D13, S9, BBE247, CSR16, CSR26 (dumb-bell) were utilized for preparation of oval and dumb-bell foundation crosses (FC). Selected oval FCs were utilized as female parents with dumb-bell breeds (in three-way cross) and oval and dumb-bell FCs as lines x testers in (OxO)x(DxD) four-way crosses preparation by employing partial diallel cross method. The parental breeds, foundation cross, single-cross, three-way cross and four-way cross hybrids were brushed together. After third moult, 250 larvae with three replications each were retained and reared by following the standard rearing method (Datta, 1992) during different seasons of the year viz., summer, rainy and winter. To evaluate the pre- cocoon, cocoon and post-cocoon performance, 13 important economic traits that govern quality and quantity of silk output viz., fecundity, larval duration (total and 5 th age), yield / 10,000 larvae by number, Yield/10,000 larvae by weight, cocoon weight, shell weight, cocoon shell percentage, filament length, filament size (denier), raw silk percentage, neatness, renditta and boil-off loss were evaluated. Hybrid vigour in respect of both foundation cross (FCs) and single-cross hybrids was estimated for all the traits (except total and 5 th age larval duration) by following the formula as detailed below. F1 – MPV H% = --------------- x 100 MPV H% = Heterosis percentage, F1 = Mean value of the F1 hybrid, MPV = Mean of the mid parent value (P1+P2 / 2),