| Crosses selected on the basis of sca effects and per se performance in
different environments over years are presented in Table
3. The only cross WH157 x Narbada 4 was found desirable under all the
environments which involved both parents as good general combiner under
all the environments. This cross may be exploited through conventional breeding
methods which make use of only additive and additive x additive type of
gene effects. The cross combinations Kharchia 65 x WH157, WH157 x Narbada
4, K68 x IWP72 under irrigated, WH157 x WL711 and WH157 x Narbada 4 under
rainfed and WH157 x Narbada 4 under saline environments were found desirable
for this trait. These crosses involved at least one parent having good general
combining ability. Therefore, such combinations could through up desirable
transgressive segregants if the additive genetic system present in the good
combiner and complementary epistatic effects act in the same direction to
maximize the desirable plant attribute. The estimates of the components of genetic variation D, H1, H2, F alongwith their ratios are presented in Table 4. The D and H1 were found significant in all the three environments over years. This indicated the role of both additive and non-additive components of variation. The magnitude of H1 was higher than D. The estimated degree of dominance was more than one except EII during 1980-81, suggesting over dominance and thus predominance of non-additive type of gene effects. These results support the results obtained through combining ability analysis. Significant and positive value of F estimate revealed that the frequency of dominant alleles was higher than that of recessive alleles in EII and EIII during 1980-81. In rest of the environments F values were non-significant. The ratio H2/4H1 indicated slight deviation from symmetrical distribution of genes with positive and negative effects in EI and EIII during 1979-80, while in rest of the cases asymmetrical distribution was observed. The ratio h2/H2 indicated that at least one or two dominant genes or gene groups were responsible for controlling this character under different environments over the years. The narrow sense heritability of this character was low under normal ; low to high under saline and moderate to high under rainfed environments. From the foregoing discussion it is now clear that both additive and non-additive types of gene effects were responsible for 1000 kernel weight in wheat. The breeding plan such as recurrent selection which can exploit both the fixable as well as non-fixable components of genetic variation is suggested. In this situation biparental mating may increase the frequency of desirable recombinants and hasten the rate of genetic improvement. SHARMA & SINGH (1976) and SHARMA et al. (1977) also suggested population breeding in the form of biparental mating between selected recombinants to exploit the additive and non-additive gene effects in wheat. References GRAFIUS, J.E. 1956. Components of yield in oats, a genetic interpretation. Agron. J. 48 : 419-23. GRIFFING, B. 1956. Concept of general and specific combining ability in relation to diallel crossing system. Aust. J. Biol. Sci. 9 : 463-93. HAYMAN, B.I. 1954. The theory and analysis of diallel crosses. Genetics 39 : 789-801. MULLER, T.C., S.R. CORTAZEV, P.C. PARODI & V.P. ALVARDO. 1971. Hybrid vigor combining ability and gene action in six wheat genotypes (Triticum aestivum L.) SRIVASTAVA, R.B., O.P. LUTHRA, D. SINGH & K.C. GOYAL. 1981. Genetic architecture of yield, harvest index and related traits in wheat. Cereal Res. Communcations 9 : 31-37. SHARMA, G. & R.B. SINGH. 1976. Inheritance of plant height and spike length in spring wheat. Indian J. Genet. Pl. Breed. 36 : 173-183. SHARMA, J.C., Z. AHMAD & A.N. KHANNA. 1977. Studies on gene effects in relation to wheat improvement. National Seminar on Genetics and Wheat Improvement. Abstract P. 20. |
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