The genetical relationship between height and yield in wheat

Abstract

Apart from a higher proportion of non-additive variation for yield, the analysis of four diverse wheat varieties indicated that the presence and direction of dominance, as well as the incidence of duplicate interactions was similar for both yield per plant and final plant height. The study of F3, F4 and F5 lines showed that these two characters were positively correlated. This correlation occurred irrespective of plant spacing. Selection for height was found to be more effective at improving yield than direct selection for yield. The positive correlation between height and yield was observed among a set of inter-varietal chromosome substitution lines. At least one chromosome from each homoeologous group was shown to participate in this correlation, suggesting that all the chromosomes of wheat carry genes affecting this relationship. Although intermating studies provided evidence of “breakable” repulsion linkages between genes for height and yield, the predominant organisation of the genes for these two characters was either “tight” coupling linkages or pleiotropy or both. Because so many genes were evidently involved it is argued that pleiotropy must be the major contributor to the positive relationship between the two characters. This positive correlation is contrary to the breeders' selection aims of short-straw with high yield, so that the genes responsible will be maintained at intermediate frequencies in breeding populations. It is suggested that a way of utilising their full potential in breeding could be to introduce independently acting genes for dwarfism and then to select for tall, high-yielding plants. This selection for “tall-dwarfs” might be accomplished by using the Norm 10 dwarfing genes, Rht1 and Rht2, which have proved to be so successful in the development of the high-yielding semi-dwarf wheats of the “Green Revolution”.