Reproductive development of white clover (Trifolium repens L.) is not impaired by a moderate water deficit that reduces vegetative growth:: II.: Fertilization efficiency and seed set

The reproductive potential of white clover (Trifolium repens L.) plants is favored by moderate water deficits that reduce vegetative growth without impairing development of inflorescences, florets, and ovules. We examined the effects of this tape of water deficit on reproductive characters involved in pollination, ovule fertilization, seed set, and seed filling. Two experiments were conducted under controlled conditions with four genotypes either in soil columns or vermiculite, and with Various levels of water deficit that were maintained for 68 d. Treatments were classified as moderate (M) and severe (S) water deficit on the basis of the reduction of leaf relative water content (RWC) compared with the ell-watered plants (C) and of previously established relationships between RWC, soil water potential and vegetative growth. Florets were hand pollinated and seed set was determined in all possible cross-pollinations between pollen and florets from plant, subjected to C, M, or S treatments. Pollen viability declined as water deficit increased. Control and M plants had similar high levels of nectar production. In S plants, the proportion of florets containing nectar was reduced by 60 to 70%. Pollen from S plants induced a lower fertilization efficiency than pollen from C or M plants. Most of the reduction of seed set by severe water deficit, however, was linked to the decrease in female plant water status resulting in abortion of embryos. These results show that pollination, fertilization, seed setting, and seed filling can be limited by a severe water deficit applied during reproductive development. A moderate water deficit characterized by an avoidance of leaf dehydration and a reduction of vegetative growth did not impair fertilization efficiency and resulted in maximum seed set and thousand seed weight, compared to C and S plants.