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Heterosis and Combining Ability Estimates for the Total Number of Eggs Laid Per Female in Silkworm, Bombyx Mori L.

H A Rashid
Govt. Rajendra College, Faridpur

M K Ahsan
Department of Zoology, Rajshahi University

S M Rahman
Department of Zoology, Rajshahi University

Abstract/ Executive Summary:

Heterosis and combining ability for total number of eggs laid per female silkworm Bombyx mori L were investigated in a six parent diallel crossing programme in four rearing seasons. Magnitude of heterosis varied from seasons to season and was not consistent over characters. Effect of season was important in the expression of genetic variances and other parameters studied. Considerable amount to heterosis was obtained in the crosses where parents Nistari Oval (G), BSRI-98 and BV-High were involved. Parental performance as judged by general combining ability quantities indicated that BSRI-98 was the best general combining parent in all the rearing seasons. The variance due to the specific combing ability (σ² sca) was higher than the general combining ability (σ²gca) in all seasons, indicating the preponderance of non-additive gene action in inheritance of that trait. Majority of the crosses showing significant sca effects had either one or both the parents were good general combiners. Thus the combining ability of parents may be considered as a reliable guide in the prediction of the yield potential of those crosses. The crosses Nistari Oval (G)×BSRI-98, Nistari×BSRI-98 and BSRI-95× Nan Nung 7B are recommended for the commercial exploitation of heterosis as an important egg producing breeds in majority of the rearing seasons.

Keywords: Heterosis, combining ability, Bombyx mori.

Location: Department of Zoology, Rajshahi University

Start Date:

End Date:

Program Area: Development of Host and Medicinal Plants

Commodity:

Objectives:

To study the heterosis and combining ability for total number of eggs laid per female silkworm Bombyx mori L were investigated in a six parent diallel crossing programme

Methodology:

In the present experiments five multivoltine viz. Nistari (P₁), Nistari oval (G) (P₂), BSRI-95 (P₃^₎, NanNung-7B (P₄), BSRI-98 (P₅) and one bivoltine viz. BV (High) P₆) varieties of silkworm, B. mori. were utilized as parents and were crossed following diallel crossing including reciprocals. The parents and 30 hybrids were reared in randomized block design with three replications in four rearing seasons corresponding to commercial rearing seasons as practiced by farmers in Bangladesh. The rearing was conducted in the Sericulture Research Laboratory of the Department of Zoology, Rajshahi University. The total number of eggs laid by an individual female moth was counted. A mean of 20 layings for each replication was used for statistical analysis. The average performance of parents and F₁ hybrids (average over reciprocal crosses) over replications were used for calculating the magnitude of heterosis. The general and specific combining ability effects and variances were estimated following Griffings (1956b) Method I. In the model II the experimental material is to be regarded as the population about which inference are to be made. The objectives are to compare combining abilities of the parents when the parents themselves are used as tester and to identify the yielding combinations.

Source of Information:

Article Link (Online Journal):

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Total Budget (Tk.) :

Achievement/Findings:

The general combining ability effect of individual parents with their corresponding standard error. Parent BSRI-98 was found to be the best general combiner in all the rearing seasons. The results revealed that BSRI-98 and BSRI-95 were positively significant in all the rearing seasons but BV-High was positively significant only in S-1. On the other hand, majority of the other parents showed negatively significant result. These good general combiners could effectively be utilized in the future hybridization programme for developing high yielding varieties. High sca effects of those crosses might be the result of the complementary type of genetic interactions. Cross 11 (P₃ × P₅) in S-3 exhibited significant heterosis as well as they were the product of good general combining parents. But they did not show significant specific combing ability (Tables 2 and 6). High sca denotes, a high heterotic response but this may be due to the very poor performance of the parents in comparison to their hybrids. With the same amount of heterotic effect the sca effect may be less where the mean performances of the parents were higher. This suggests that the selection of cross combinations based on the heterotic response would be more realistic.over better parents are very limited in this study which is always desirable for maximum gains and for this, there is need for searching genetically diverse materials.

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