The effects of moisture supply and defoliation during flowering on seed production and hardseededness of Trifolium subterraneum L

Abstract

The effect of length of the flowering period on seed production characteristics of 3 cultivars of subterranean clover (Trifolium subterraneum L.) was determined by varying the period of watering postflowering. The subterranean clover cvv. Nungarin, Seaton Park and Woogenellup were grown in polystyrene boxes and given 1 of 4 watering treatments: continuous (WC); until approximately 34 days after flowering commenced (WE); until Nungarin finished flowering (WN); as for WE but with watering recommenced after plants became wilted (WEL). Plants were either undefoliated or were repeatedly defoliated during flowering. Flowering in all 3 cultivars was terminated early and seed yields were reduced by WE (e.g. WC v. WE for Seaton Park, 1620 � 61 v. 320 � 61 kg/ha), but each of the cultivars was able to produce appreciable numbers of viable seed on the WE treatment, ranging from 406 � 95 seeds/dm2 for Woogenellup to 791 � 95 seeds/dm2 for Seaton Park. WEL increased seed size in all cultivars by approximately 50%, and increased seed numbers in Seaton Park to 1083 � 106 seeds/dm2. Nungarin produced most seeds on the WN treatment (1232 � 104 seeds/dm2), but approximately half of these were lost if the soil was kept moist during seed maturation. In comparison, little loss of seed was detected from Seaton Park and Woogenellup under continuous watering, possibly due to differences between cultivars ii seed dormancy and periods of exposure of maturing seeds to moisture. The development of initial hard seeds in Nungarin and undefoliated Seaton Park was adversely affected by continuous moisture. Repeated defoliation during flowering reduced seed yields in all cultivars (e.g. UD v. D for Seaton Park, 1130 � 44 v. 310 � 46 kg/ha), due to decreases in both seed numbers and size. The results indicate that choice of maturity of subterranean clover cultivars for areas with unreliable spring rainfall is not necessarily restricted to those early maturing cultivars which will always finish flowering prior to moisture restrictions.