Comparison of the effect of mur and nap cytoplasms on the performance of intercultivar summer rape hybrids

Abstract

The performance of six isogenic pairs of male fertility restored, hand-crossed, summer rape (Brassica napus L.) hybrids, in the mur and nap cytoplasms, were investigated in four Manitoba environments. Hybrids in both cytoplasms exhibited high-parent heterosis for seed yield, total dry matter (TDM) and, to a lesser degree, harvest index (HI). Negative high parent heterosis for days to flowering, days to maturity, oil concentration and protein concentration was observed. Combined over hybrids within cytoplasms, the mur and nap cytoplasmic hybrid groups differed in oil concentration in all environments, and in protein concentration in one of four environments. Similarly, the mur hybrid group was lower-yielding and had lower TDM, HI and oil concentration, but higher protein concentration than the nap hybrid group. Even though there are some biological costs associated with the mur cytoplasm, especially for oil concentration, it appears that the mur cytoplasmic male sterility (CMS) system has good potential for use in summer rape hybrid cultivar breeding and commercial hybrid seed production, since hybrids in the mur cytoplasm display heterosis for many traits in absolute terms. Key words: Biological cost, Brassica napus L., cytoplasmic male sterility, heterosis, hybrid