Key words: Triticum aestivum, cross prediction, transgressive segregation, field resistance


Introduction

Leaf rust of wheat (Triticum aestivum L. em. Thell.) caused by Puccinia recondita Rob. ex. Desm, is the most common and widely distributed foliar disease of wheat in the world (Statler and Miller 1982: McIntosh et al. 1995). The most effective way of controlling this disease is to develop resistant cultivars. Currently, there is much interest in the type of resistance that is expressed under natural field conditions as opposed to seedling resistance (Kuhn et al. 1980; Knott 1982; Yadav et al. 1992; Knott and Yadav 1993; Broers et al. 1996). This form of resistance usually is longer lasting and quantitative in inheritance. The importance of this disease led plant breeders to attempt new breeding approaches for developing resistant genotypes. The use of transgressive segregants which surpass the best parent has been considered a valuable approach for developing resistant genotypes (Smith 1966; Wallwork and Johnson 1984; Broers and Jacobs 1989; Yadav et al. 1992). Quantitative genetic theory provides models for predicting frequencies of transgressive segregants in the progeny of crosses between two pure breeding lines. Jinks and Pooni (1976, 1980) have shown how estimates of genetical parameters can be used to predict frequency of transgressive segregants. that would appear in later generations. In the present study, attempts were made to predict the frequency of transgressive segregants for field resistance using various mating designs including diallel, generation mean analysis, biparental matings and selfings and to test the validity of the predictions by isolating the transgressive segregants in the different generations.

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