SALINITY AFFECTS THE TIMING OF PHASIC DEVELOPMENT IN SPRING WHEAT

Understanding effects of environmental factors on crop phenological de velopment is useful for predicting crop growth stages and scheduling m anagement practices. We evaluated the effect of salinity on the rate o f leaf appearance and the duration of critical stages of growth in whe at (Triticum aestivum L.) in terms of both thermal unit (TU;degrees C day) and phyllochron intervals. Two hard red spring wheat cultivars, Y ecora Rojo and Anza, were grown two cropping years in greenhouse sand cultures and outdoor field lysimeters. In each case, two saline treatm ents were compared with a nonsaline control. The sand cultures were ir rigated with complete nutrient solutions to which NaCl and CaCl2 were added. The electrical conductivities, kappa(iw), were 2.0, 14.3, and 1 8.1 dS m(-1) in 1989 and 1.7, 12.2, and 15.1 dS m(-1) in 1990. The kap pa(iw) for the held lysimeters were 0.9, 10.7, and 17.2 dS m(-1) in 19 89 and 0.8, 11.4, and 17.1 dS m(-1) in 1990. Leaf appearance rate was determined by regressing the number of mainstem leaves against cumulat ive TU. In all treatments, the cultivars differed in both rate and dur ation of leaf appearance. The phyllochron increased with salinity. Lea ves emerged more slowly in the greenhouse than in the field. Durations of the vegetative stages (degrees C day) from sowing to the initiatio n of the bag leaf and its subsequent appearance were relatively insens itive to salinity inasmuch as increases in leaf plastochron (TU betwee n the initiation of successive leaves on a culm) and leaf phyllochron were balanced by decreases in leaf number. However, for both cultivars , salinity significantly reduced the thermal time between sowing and t he reproductive phenological stages.