The relationship between pre-anthesis development and seed yield of spring rape (Brassica napus L.)

Abstract

Experiments were carried out to determine the influence of flowering time and the pattern of pre-anthesis development on the seed yield of spring rape. The responses of six cultivars to variation in sowing date at a site 100 km east of Perth indicated that the duration of the vegetative phase and the time of the season at which seed development commenced were both important determinants of seed yield. Seed yields decreased with a reduction in the duration of vegetative development and an extension in the time between 1 October and first flowering. These data suggested that an optimal flowering time for this and similar environments would, assuming a mid-June sowing, be one that allowed for at least 100 days of pre-anthesis development and ensured that seed development commenced no later than 1 October. In a controlled environment experiment, different patterns of pre-anthesis development induced in the cultivar Target by exposure to different photoperiodic regimes were associated with substantial variation in seed yield. This variation in seed yield was primarily associated with differences in the duration of the stem elongation phase: an increase in duration resulted in the production of greater numbers of flowers (and pods) per plant and ultimately greater numbers of seeds per plant. As seed size was largely unaffected by variation in photoperiod during pre-anthesis development, extension of the stem elongation phase was accompanied by significant increases in seed yield. Substantial genotypic variation in the duration of the stem elongation phase was observed among a group of spring rape cultivars and their F1 hybrids grown in a controlled environment comparable with that prevailing in the field during this phase of development. Longer periods of stem elongation were accompanied by increased pod production and higher seed yields. Evidence from this and earlier studies indicated that there was sufficient genetic variation in pre-anthesis development to facilitate yield improvement through selection based on developmental characters. The utilization of controlled environment facilities in conducting such a selection program is discussed.