HETEROSIS FOR YIELD AND RELATED CHARACTERS IN PEA

To determine the levels of heterosis in Fl hybrids, four current pea ( Pisum sativum L.) cultivars from southern Australia were used as femal e parents and crossed with 18 introduced genotypes. The 22 parents, 72 F1 hybrids and, depending on the environment, either 54 or all 72 F2 families were grown in replicated plots in four environments. Grain yi eld, total dry matter, harvest index, branches per plant, pods per pla nt, seeds per pod, hundred seed weight, plant height, onset of floweri ng and flowering periods were evaluated. For both the Fl and F2 genera tion, heterosis was determined as the superiority over the mid-parent and also over the better parent. In addition, the superiority over the best commercial cultivar was calculated. Most hybrids were higher yie lding than their mid-parent but were less stable in yield across envir onments. Four Fl hybrids were significantly higher yielding than the b est parent, by up to 26%. There were significant correlations between F1 hybrid and mid-parent value for plant height, pods per plant and hu ndred seed weight but not for yield. Overall, grain yield heterosis wa s mainly due to more pods per plant in the hybrids. The level of heter osis for yield in a poor yielding environment was higher than that in a high yielding one. Both additive and non-additive gene effects were important in the expression of all studied traits. The average level o f heterosis for grain yield and total dry matter in the F2 population was half of that in F1 hybrids. The low level of inbreeding depression from the Fl to the F2 generation suggested that epistatic gene action also contributed to the expression of grain yield. Some F2 population s maintained the high yield levels of the corresponding F1 hybrids.