Genetical and environmental studies on the protein content of white haricot beans, phaseolus vuigaris l., in Uganda.

Abstract

The present study has been initiated to investigate the genetical and environmental factors affecting the protein content of white haricot beans. A study of this nature requires the use of crude protein and methionine techniques to analyse large numbers of plant lines quickly and efficiently. Two techniques are considered suitable for estimating percentage crude protein - the Kjeldahl-Markham technique for limited numbers of samples and the automated nitrogen analyser for the large numbers of breeding samples. A microbiological method has been chosen for the analysis of available methionine. These protein and methionine techniques are then used to assess the genetic variation in the collection of white haricot beans. From this collection, twenty five varieties have been selected and assessed in Variety Trials over four different seasons to estimate the environmental effects on protein and methionine content. There is a considerable environmental effect on protein content and no effect on methionine content. In the light of this environmental effect on protein content, the effect of different levels of fertiliser treatment are considered. The results show a significant variety x fertiliser treatment interaction for protein content, but not for methionine content. The protein-yield relationship has also been considered in relation to the increasing levels of fertiliser and the results show considerable variation according to the type of growth habit of the variety. The results indicate that for the protein inheritance study, it is important to grow all generations in one season and under as near to possible uniform environmental conditions. A quantitative genetical approach to the study of protein inheritance has been adopted, using F1, F2 and F3 generations of 7x7 non reciprocal diallel of selected contrasting parents. The genetic control of protein content has been studied using diallel cross analysis of Jinks and Hayman and the interpretation is based on the graphical presentation of the results of the analysis. The results suggest that protein content is controlled by a series of genes with minor effects which are additive but with partial dominance for low protein in at least some of the loci. An assessment of the potential of the varieties has been made on the basis of their general and specific combining ability for protein. The results obtained from the various aspects of the study are discussed in relation to the improvement of the bean crop.