Reproductive Development of White Clover (Trifolium repens L.) is Not Impaired by a Moderate Water Deficit That Reduces Vegetative Growth

Field experiments have shown that water deficit can either increase or decrease white clover (Trifolium repens L.) seed yield depending on its intensity. In order to explain this behavior, we evaluated the effect of water deficit intensity on the components of plant reproductive potential: number of reproductive stolons produced per plant (NSr), inflorescences per reproductive stolon (NI), viable florets per inflorescence (NFv) and ovules per floret (NO). Four experiments were conducted in greenhouse or growth chamber on white clover plants grown in large or small soil columns, or in small pots with vermiculite. Water supply was managed to maintain relatively constant values for predawn soil water potential and midday leaf relative water content (RWC) during the deficit period (20 to 68 d). Water deficit treatments were classified as moderate (M) or severe (S) on the basis of the reduction of RWC compared with the well-watered plants (C) and of previously established relationships between RWC, soil water potential and vegetative growth. The development of inflorescences, florets and ovules were largely unaffected in M plants, while vegetative growth was depressed by reductions in leaf number per stolon (up to 30%), leaf area (30 to 40%), and by inhibition of stolon branching. Moderate water deficits induced an increase in the percentage of reproductive stolons per plant and reproductive phytomers per stolon. Although this positive effect on the reproductive to vegetative balance was generally observed with S water deficit, the reproductive potential of S plants was strongly depressed relative to C and M plants because of reduced stolon branching, phytomer production, and increased inflorescence and floret abortion. These results show that inflorescence, floret and ovule development of white clover were not impaired by a moderate water deficit that reduced vegetative growth, and suggest good prospects to manage optimal soil-plant status to maximize potential of seed production.