Analysis of heterosis and recombination loss for fitness and productivity traits in different hybrids of mulberry silk moth Bombyx mori

Abstract

AbstractThree different races of lepidopteron silk moth Bombyx mori were used in reciprocal and inter se crosses to determine heterosis effects at F1 and recombination loss at the F2 generation for three fitness traits (fecundity, larval duration, survival rate) and four productivity traits (larval weight, cocoon weight, shell weight, filament length). Eleven mating types were represented in the present study, including three pure breeds and a variety of F1 and F2 populations arising from regular and reciprocal crosses, respectively. Equations were derived to evaluate heterosis, maternal and overdominance effects for the above traits. Estimates of heterosis and overdominance effects revealed significant heterosis effects for all the traits, but overdominance was only seen for larval duration (favorable effect) and survival rate (unfavorable effect). Maternal effects were significant for the majority of the traits under study. The results revealed significant reduction for all the quantitative traits from F1 to F2, except for larval duration. The most obvious explanation for the reduction of fitness parameters and productive traits is the reduction in heterozygosity from F1 to F2 (it is expected that one half of the heterozygosity of F1 is lost in F2). For larval duration this explanation seems insufficient and breakdown of epistatic gene effects (i.e. recombination loss) has been suggested.