Comparative performance of some bivoltine silkworm ( Bombyx mori L . ) genotypes during different seasons

1 Division of Sericulture Mirgund, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir Shalimar Campus, Srinagar -191 121, India. 2 Division of Pant Breeding and Genetics, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir Shalimar Campus, Srinagar -191 121, India. 3 Division of Agricultural Statics, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir Shalimar Campus, Srinagar -191 121, India.


INTRODUCTION
Jammu and Kashmir is the only traditional bivoltine belt in the country, which because of salubrious climatic conditions for silkworm rearing and mulberry cultivation can produce quality bivoltine silk.Lack of productive silkworm breeds/hybrids suited to agro-climatic conditions of J&K state has been identified as one of the major constraints in boosting cocoon production (Trag et al., 1992).Realizing this, some new silkworm breeds were evolved by the Sericulture Division of Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir by utilizing the genetic variability of existing germplasm resources (Kamili et al., 2000).Season and region specific studies of silkworm Bombyx mori L. are of greater importance in identifying and understanding the adaptability of silkworm genotypes which are largely influenced by climatic factors (Vijayalakshmi et al., 2014).Attempts have been made by several researchers to identify season/region specific breeds throughout the country (Gangwar, 2012, Senapati and Hazarika, 2014, Vijayalakshmi et al., 2014.Presently, the commercial silkworm rearing in the valley is practiced in spring season only.Extension of rearing to *Corresponding author.E-mail: asmaskuastk@rediffmail.com Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License other seasons is practically feasible to boost cocoon production and to increase the economic viability of sericulture in the state (Raja et al., 1999).This necessitates the synthesis/identification of breeds/hybrids suited to different rearing seasons.Although, some information about relative performance of a few pure breeds in different seasons has been generated by Malik et al. (1999) and Malik et al. (2005), yet there is no information about performance of other promising genotypes available in the germplasm bank in different seasons.The present experiment was, therefore, undertaken to study the comparative performance of twenty-six vis-a-vis two check breeds of bivoltine silkworm (Bombyx mori L.) for their suitability to spring and summer rearing seasons.

RESULTS AND DISCUSSION
The mean performance of 28 bivoltine silkworms is presented in Table 1.No genotype displayed a significant superior performance vis-à-vis check breeds (NB 4 D 2 and SH 6 ) in all the metric traits under study.However, several genotypes registered higher performance in several subsets of traits.For example in spring (E 1 ), CSR 2 displayed a significantly superior performance in 5 th age larval duration, single shell ratio, cocoon yield/10,000 larvae by number, pupation rate, filament length, denier and raw silk percentage.CSR 4 in weight of silk gland, single shell ratio, filament length and raw silk percentage However, judging the performance of genotypes on the basis of individual traits under different seasons becomes slightly difficult, particularly when more than twenty one component traits determine the yielding ability of a silkworm genotype (Thiagarajan et al., 1993).Screening of promising genotypes calls for consideration of cumulative effect of all yield component traits whether acting in positive or negative direction.Inherent genetic barriers like undesirable character associations make the choice still more difficult.Sericulture has several interest groups like seed producers, rearers, reelers and weavers.While traits like fecundity and hatching percentage are important for seed producers, the rearers need breeds with higher cocoon weight, shell weight, survival and low larval duration besides the higher fecundity and hatching percentage.Reelers on the other hand prefer cocoons with high silk contents, longer filament, lesser boil-off loss, less renditta and high neatness.Unfortunately in silkworm fecundity is negatively correlated with robustness and shell ratio.Similarly, length of filament is negatively correlated with reelability.Likewise, weight of cocoons and shell ratio are also negatively correlated.Therefore, it is almost impossible to find a breed with all desirable traits.Therefore, a balance is to be maintained by giving due weightage to important metric traits in deciding the superiority of any particular genotype.
In the present study, the breeds J 2 M, A and NCD displayed significantly superior performance in several subsets of traits during spring while, genotypes CSGRC-5, New race, JA 1 and Jam 21 surpassed the check breeds (NB 4 D 2 and SH 6 ) in a good number of metric traits during summer.The genotypes Sheiki II, Pampore-5, J 122 , Meigitsu, 14M, NJ 3 , NB 18 , CSR 2 and CSR 4 were significantly superior to the check breeds in several subsets of traits in both spring and summer.This information can be utilized for evolving new season specific breeds with accumulation of maximum desirable traits.Malik et al. (1993) reported that J 122 and Jam 21 were potential genotypes for spring rearing in Kashmir.Key: *Superior to SH6; • Superior to NB4D2.Malik et al. (2005) reported that genotypes Jam 21 and CSR 4 hold promise for commercial exploitation during both spring and summer seasons.These results are in general agreement with (Gangwar, 2012, Senapati and Hazarika, 2014, Vijayalakshmi et al., 2014.

Conclusion
The breeds J 2 M, A and NCD displayed significantly superior performance in several subsets of traits while, genotypes CSGRC-5, New race, JA 1 and Jam 21 surpassed the check breeds (NB 4 D 2 and SH 6 ) in a good number of metric traits during summer.The genotypes Sheiki II, Pampore-5, J 122 , Meigitsu, 14M, NJ 3 , NB 18 , CSR 2 and CSR 4 were significantly superior to the check breeds in several subsets of traits in both spring and summer.These genotypes can further be tested over seasons/years to confirm the stability of their performance.Moreover, this information can be utilized for evolving new season specific breeds with accumulation of maximum desirable traits.
. J 2 M in 5 age larval duration, weight of silk gland, shell ratio and raw silk percentage.NJ 3 in 5 th age larval duration, shell ratio and raw silk percentage.NB 18 in 5 th age larval duration, denier and raw silk percentage.Same trend was observed during summer (E 2 ), wherein, 14M surpassed the check breeds in 5 th age larval duration, weight of silk gland, filament length, denier and raw silk percentage.NB 18 displayed superior performance in 5 th age larval duration, filament length, denier and raw silk percentage.Meigitsu in 5 th age larval duration, weight of silk gland, denier and raw silk percentage.14M in 5 th age larval duration, weight of silk gland, single shell ratio, filament length and denier.Sheiki II and Pampore-5 in 5 th age larval duration, weight of silk gland and denier.A in 5 th

Table 1 .
Mean performance of twenty eight genotypes for fourteen metric traits during spring (E1) and summer (E2) seasons.