Genetic architecture of grain weight in durum wheat under normal and late sown environments

S.N. Sharma* and R.S. Sain

Department of Plant Breeding and Genetics, Agricultural Research Station, Durgapura, Jaipur, India

Summary

Twelve basic generations, namely, P1, P2, F1, F2, BC1, BC2, BC1self, BC2self, BC11, BC12, BC21 and BC22 of three crosses involving six diverse cultivars of durum wheat were studied under normal and late sown conditions to understand the nature of gene effects on grain weight. The 10-parameter model was found adequate only in the two crosses to account for the variability in generation means under normal sown environments. However, in other cases even the 10-parameter model did not fit the data, confirming that more than trigenic interactions or linkages were involved in the inheritance of this trait. Of the epistatic interactions, trigenic interactions were invariably more important than other gene effects in the genetic control of grain weight in durum wheat. Additive x additive (i), additive x additive x dominance (x) and dominance x dominance x dominance (z) epistatic effects contributed maximum than other effects towards significant heterosis. Duplicate epistasis in sets of three genes was frequently observed. High magnitude of inter-allelic interactions at digenic and trigenic level and manifestation of high degree of heterosis and inbreeding depression,breeder should follow diallel selective mating and biparental mating which can mop-up the genes to form superior gene constellations interacting in a favorable manner to accelerate the pace of its genetic improvement.

Key words: durum wheat, gene effects, duplicate epistasis, heterosis, non-allelic interactions

Introduction

Durum or macaroni wheat, Triticum durum (2n = 4x = 28, genomes AABB) is grown on about 30 million hectares and accounts for almost 8 percent of total world wheat production. It is the second important cultivated species of the genus Triticum in India, occupying about 2.5 million hectare and has a lot of potential both for domestic consumption and for export market since durum wheat is used for making special products. Despite its importance for the human diet little progress has been made in improving the yield and nutritional qualities on durum wheat. Historically durum wheat has received insufficient attention from plant breeder. Therefore, any efforts to increase yield in durum will be directly supportive to boost up the over all wheat production of the country and it could be helpful to meet out the food requirements for the burgeoning population. Secondly, the surplus durum wheat could be exported in the international market to earn foreign currency.

Generally, the yield levels of durum are low as compared to bread wheat under irrigated as well as rainfed conditions. Systematic attempts for improvement in durum are needed through manipulations of various yield components. Grain weight is an important yield contributing component particularly under high temperature conditions (Chowdhery et al. 1996; Nayeem and Veer 2000). The exploitation of genetic information has not been very well demonstrated for this vital yield contributing trait in durum. The choice of plant breeding methodology for upgrading the yield potential largely depends on the availability of reliable information on the nature and magnitude of gene effects present in the population. Diallel analysis, although effective and most widely used, does not provide the estimates of non-allelic interactions. Epistasis, which is known to play a major role in the expression of heterotic potential, has been reported by Jinks (1955), Hayman (1958), Brim and Cockerham (1961), Gamble (1962), Hill (1966), Matinzinger (1968) and Stuber and Moll (1974), clearly indicated the role of epistatic gene actions besides additive and dominance type. Hence, it is essential to know precisely the genetic architecture of character(s) for further improvement of yield.

*Corresponding author