A quantitative analysis of resistance to mycosphaerella blight in field pea

Mycosphaerella blight, caused mainly by Mycosphaerella pinodes (Berk. and Blox.) Vestergren, is the most important foliar disease on field pea (Pisum sativum L.) in western Canada. A quantitative trait analysis of resistance to M. pinodes was undertaken on five crosses with reciprocals of P. sativum to examine broad-sense ([H.sup.2]) and narrow-sense ([h.sup.2]) heritability, minimum number of genes involved (MNG), mid-parent heterosis (MPH), cytoplasmic inheritance, and epistasis. Mean [H.sup.2] was 0.75 (range 0.67-0.80) and mean [h.sup.2] was 0.59 (range 0.41-0.70), indicating that additive variance is important and that improvement in resistance can be achieved through breeding. Mean MNG was 2.16 genes (range 0.06-6.22), indicating that genes for resistance differed among parent lines. Mean MPH was 50% (range 47-57%), indicating that heterosis did not influence the expression of resistance to M. pinodes. There was no difference between the mean of any [F.sub.1] population and its reciprocal, indicating lack of maternal inheritance. The mean of the epistatic points was -0.01 (range -0.1 to 0.12), indicating that epistasis was not important in these crosses. These results will further the understanding of the natural genetic diversity for disease resistance to M. pinodes in P. sativum.