Rapeseed adaptation in northern New South Wales. I. Phenological responses to vernalization, temperature and photoperiod by annual and biennial cultivars of Brassica campestris L., Brassica napus L. and wheat cv. Timgalen

Abstract

Two experiments were conducted to investigate the developmental responses of annual and biennial B. campestris and B. napus cultivars and one annual wheat cultivar to vernalization, temperature and photoperiod at Tamworth, N.S.W.

In the first experiment, mean daily temperature and photoperiod in the field varied within the ranges 6–26°C and 11–15 hr respectively. Serial plantings between April and September, the use of low intensity supplemental illumination, and vernalization treatment of young seedlings provided additional environmental variation. Wheat was insensitive to vernalization, and annual rapeseed cultivars showed significant facultative responses to vernalization, but the variation in phase duration of all annual cultivars was largely accounted for by correlation with temperature and photoperiod. The phenological responses of biennial cultivars to temperature and photoperiod were confounded by their unsatisfied vernalization requirements, because the response to vernalization treatment was incomplete.

In the second experiment, the influence of plant age on the vernalization requirements of four cultivars of rapeseed was investigated in a glasshouse. There was a small response to vernalization in annual cultivars, but their planting date would not be dictated by obligate requirements for winter chilling. Biennial cultivars could not be effectively vernalized as seeds, but as green plants were shown to require 15–19 weeks of chilling at l°C to enable them to flower. With insufficient chilling, some biennial plants remained vegetative; flowering occurred in others, but tended to be delayed and variable. Planting dates of biennials would therefore be strongly influenced by their vernalization requirements, and planting should be sufficiently early to allow seedling growth before the stimulus is received during winter.

The prediction of phenological pattern and the breeding of cultivars better adapted to local conditions are discussed.