OVULE DEVELOPMENT AND DETERMINATION OF SEED NUMBER PER POD IN OILSEED RAPE (BRASSICA-NAPUS L)

Seed number per pod at maturity over the terminal raceme of single plants of oilseed rape is closely correlated to the percentage of ovules with complete embryo sacs (ovule fertility) at flower opening. Approximately one-third of the ovules did not contain an embryo sac and sterility, due to the absence of embryo sac, accounted for most of the difference between the numbers of ovules and seeds. Within the terminal raceme, both a decreased proportion of fertile ovules and a lower number of ovules per ovary in apical flowers contributed to the lower number of seeds per pod in the mature apical pods compared to the basal ones. A study of ovule development before flower opening showed that differences in the differentiation of the embryo sacs arose before the buds were 4.0 mm long and probably involved the stages of meiosis II and/or differentiation of the chalazal megaspore.