PLANT SPACING, DENSITY, AND YIELD OF WHEAT SUBJECTED TO POSTANTHESIS WATER DEFICITS

The optimum planting density for Gutha wheat (Triticum aestivum L. eme nd. Thell.) grown in mediterranean-type environments varies with site and season. This study investigated the influence of postanthesis wate r deficits on the water relations and yield of wheat sown at different plant densities with even and uneven plant densities along the row. U nevenness of machine planting resulted in a yield reduction of 20% com pared with evenly spaced plants in plants subjected to postanthesis wa ter deficits, but no yield reduction was observed in irrigated wheat. Wheat at high densities (100 and 200 plants m(-2)) developed lower lea f and ear water potentials than plants at low densities (25 and 50 pla nts m(-2)) during postanthesis water deficits. The greater deficits, h owever, did not reduce yields. Grain yields were generally lower at de nsities of 25 and 50 plants per square meter than at 200 plants per sq uare meter when postanthesis water deficits developed, but not when ir rigated. The later-formed tillers (Tillers 2, 3 and 4), which were onl y produced at low densities, had smaller thousand-grain weights compar ed to those of the mainstem and the first tiller when water deficits w ere induced during the postanthesis period. The delay in anthesis in t he later-formed tillers was up to 20 d and this resulted in grain fill occurring at low leaf and ear water potentials. We conclude that redu cing the density of plants to reduce water use may decrease rather tha n increase wheat yield under water-limited conditions.