THE EFFECT OF VARYING LEVELS OF HYBRIDITY ON THE PERFORMANCE OF 3 POL-CMS SUMMER RAPE HYBRID CULTIVARS (BRASSICA-NAPUS L)

The Polima (pol) cytoplasmic male sterility system (CMS) has been deve loped to facilitate the commercial production of hybrid summer rape cu ltivars. Polima A-lines usually produce small quantities of viable pol len, and further, they suffer from high-temperature-induced male-ferti lity reversion at temperatures of 30 degrees C or higher. This pollen production can result in selfing and sibing of the pol A-lines, substa ntially 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 poi CMS summer rap e hybrids grown in seven environments over 3 yr were found to be minim al in this study. It is concluded that in cases where the effect of po l A-line contamination on the oil content and (or) protein content of contaminated hybrids is significant, these effects can be predicted fr om a comparison of the relative oil and protein contents of the pure p ol A-line and the pure hybrid. It is also concluded that the current 7 5% hybridity standard, set by the Canadian Seed Growers Association fo r the CMS hybrid summer rape seed lots is a reasonable initial minimum standard.