The effect of varying levels of hybridity on the performance of three pol CMS summer rape hybrid cultivars (Brassica napus L.)

Abstract

The Polima (pol) cytoplasmic male sterility system (CMS) has been developed to facilitate the commercial production of hybrid summer rape cultivars. Polima A-lines usually produce small quantities of viable pollen, and further, they suffer from high-temperature-induced male-fertility reversion at temperatures of 30 °C or higher. This pollen production can result in selfing and sibing of the pol A-lines, substantially reducing the hybridity of the field-produced hybrid seed lots. The effects of 5, 15, 25 and 35% A-line contamination on seed yield, oil content and protein content for three different pol CMS summer rape hybrids grown in seven environments over 3 yr were found to be minimal in this study. It is concluded that in cases where the effect of pol A-line contamination on the oil content and (or) protein content of contaminated hybrids is significant, these effects can be predicted from a comparison of the relative oil and protein contents of the pure pol A-line and the pure hybrid. It is also concluded that the current 75% hybridity standard, set by the Canadian Seed Growers Association for the CMS hybrid summer rape seed lots is a reasonable initial minimum standard. Key words: Polima cytoplasmic male sterility, hybrid seed production