The genetic system controlling number of spikelets per ear in macaroni wheat over environments

All India Coordinated Wheat and Barley Improvement Project, Rajasthan Agricultural University, Agricultural Research Station, Durgapura, Jaipur 302 018, Rajasthan, India

Summary

The genetic system controlling spikelets per ear was studied from twelve generations of three intervarietal crosses of macaroni wheat (Triticum durum Desf.) in two separate environments. The results of joint scaling test indicated that non-allelic interactions had a major role to control this trait in almost all the cases in both the sowing environments. Additive (d) gene effects were frequently observed significant than dominance (h). Both the digenic and trigenic interactions played a significant role in the expression of this trait in the cross HI 8062 x JNK-4W-128. Whereas, in the cross Cocorit 71 x A- 9-30-1 and Raj 911 x DWL 5002 only trigenic interaction was involved, which indicated the major contribution of trigenic interactions to control the inheritance of spikelets per ear in durum wheat. Absolute totals of the non-fixable gene effects were higher than fixable gene effects, confirmed the major role of non-additive gene effects in almost all cases. Digenic and trigenic epistatic interactions cause significant and positive heterosis in the cross Hl 8062 x JNK-4W-128 only. The dissipation of epistatic effects involving dominance in F₂ generation causes significant inbreeding depressions. Restricted recurrent selection or diallel selective mating method would be helpful in improving this trait in the material derived from the three crosses. Favorable and a suitable environment must be considered before finalizing the any breeding program for its simple inheritance to get desirable improvement for high grain yield.

Key words: durum wheat, genetic system, epistatic interactions, gene effects, heterosis.

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.

Information on the genetic parameters associated with the inheritance of a character is a prerequisite to plan a sound-breeding program for its improvement. Yield is a very complex character (Adams 1967), direct improvement for which is not effective. Earlier, breeders suggested tangible advancement of yield components as a possible method for yield improvement. Number of spikelets per ear is one of the important yield contributing component. Some studies have already been conducted in the past revealed that grains per ear can be increased by increasing the number of grains per spikelet. Hence, genetic information concerning the nature of gene action for number of spikelets per ear would be a valuable tool for breeding higher yielding cultivars. The inheritance of this trait was already studied by a number of workers using second order statistics such as diallel analysis (Nanda et al. 1981; Singh and Anand 1971; Maloo 1978; Reddy unpub; Verma 1981). However, the use of first-degree statistics is too limited, which provide the information for nature and the magnitude of gene action (additive, dominance and epistatic) involving in controlling the inheritance of characters related to productivity. This would aid in the choice of effective and efficient breeding methods and thus, accelerate the pace of its genetic improvement of grain yield. Present study was therefore, undertaken to obtain precise information regarding the genetic system controlling the inheritance of spikelets per ear in macaroni wheat using generation means analysis. The information so obtained shall be useful in formulating a sound breeding program in this crop for its tangible advancement in the future.