Maintenance-free cryopump compressor

Abstract

The effect of fertility status and temperature conditions during floral induction on flowering, berry yield, and weight and drupelet numbers of individual berries were studied in ‘Glen Ample’ raspberries grown under controlled conditions. Withdrawal of normal fertilization prior to and at various stages during floral induction did not affect yield and berry size, but marginally advanced flowering and fruit ripening. The successive stages of floral initiation and differentiation were studied and identified by scanning electron microscopy of the uppermost lateral buds of plants grown for six weeks under naturally decreasing autumn photoperiods at temperatures of 9, 15 and 21 °C. Low temperature advanced floral initiation, and advanced and enhanced flowering and berry yield in the following season. However, at variance from earlier studies, the plants eventually initiated flower primordia even at 21 °C. Marginal low temperature and short day conditions during the last days before the temperature treatments were started on 17 September might possibly have reduced the subsequent induction requirements enough to explain this unexpected result. Correlation analyses revealed an over-all positive correlation between fruit weight and drupelet numbers (r = 0.568, P = 0.01). In berries from the early harvests, the number of drupelets per berry increased with decreasing temperature, while the numbers converged to the same level regardless of temperature in the later harvests. Based on the progress of the floral initiation process at the various temperatures, we interpret this to mean that only the early initiated flowers, that gave rise to the early maturing berries, were differentiated during the actual period of controlled temperature exposure, whereas the remaining flowers were differentiated afterwards when all plants were exposed to identical low temperature conditions. Increased femaleness under optimal floral induction conditions is in agreement with results in both monoecious and dioecious plants and circumstantial evidence suggest that, in the raspberry, this might be mediated by changes in gibberellin activity which acts as a male sexual hormone in plants and is known to inhibit growth cessation and floral initiation in raspberry.