GENETIC-DISTANCE AND ITS ASSOCIATION WITH HETEROSIS IN PEAS

The relationship between the genetic distance of parents and both the heterosis of F-1 hybrids and the variance of F-5 lines was investigate d in 72 crosses of pea (Pisum sativum L.). The genetic distance betwee n each pair of parents was estimated, using isozyme (GD(i)), morpholog ical (GD(m)) or quantitative (GD(q)) markers and finally a combination of isozyme and morphological markers (GD(i+m)). GD(m) was poorly corr elated with the other measures of genetic distance, which in turn were strongly correlated with each other. Genetic distance was moderately correlated with the level of heterosis for yield over midparent in the F-1 generation, with the highest correlation obtained from GD(i+m). G D was not significantly correlated with heterosis for yield over the b etter or best parent but it was significantly correlated with all thre e measures of heterosis for pods per plant and hundred seed weight. Th ere was no correlation between genetic distance and the level of heter osis for yield and total dry matter in the F-2 generation, but GD(i), GD(i+m) and GD(q) were predictive for the level of inbreeding depressi on in grain yield and total dry matter. When parents were high in gene tic distance, crosses produced highly transgressive segregants for bas al branches per plant, hundred seed weight, harvest index and onset of flowering. Genetic distance between parents was thus a useful measure for predicting a portion of hybrid performance and also of the varian ce of derived inbred lines. It was concluded that when choosing parent s for a cross, consideration should be given to their genetic distance as well as their overall adaptation and their yield. There is conside rable potential for optimising choice of parental combinations in the development of improved pea cultivars.