SALINITY AFFECTS THE TIMING OF PHASIC DEVELOPMENT IN SPRING WHEAT

Understanding effects of environmental factors on crop phenological development is useful for predicting crop growth stages and scheduling management practices. We evaluated the effect of salinity on the rate of leaf appearance and the duration of critical stages of growth in wheat (Triticum aestivum L.) in terms of both thermal unit (TU;degrees C day) and phyllochron intervals. Two hard red spring wheat cultivars, Yecora Rojo and Anza, were grown two cropping years in greenhouse sand cultures and outdoor field lysimeters. In each case, two saline treatments were compared with a nonsaline control. The sand cultures were irrigated with complete nutrient solutions to which NaCl and CaCl2 were added. The electrical conductivities, kappa(iw), were 2.0, 14.3, and 18.1 dS m(-1) in 1989 and 1.7, 12.2, and 15.1 dS m(-1) in 1990. The kappa(iw) for the held lysimeters were 0.9, 10.7, and 17.2 dS m(-1) in 1989 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 cumulative TU. In all treatments, the cultivars differed in both rate and duration of leaf appearance. The phyllochron increased with salinity. Leaves emerged more slowly in the greenhouse than in the field. Durations of the vegetative stages (degrees C day) from sowing to the initiation of the bag leaf and its subsequent appearance were relatively insensitive to salinity inasmuch as increases in leaf plastochron (TU between 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 the reproductive phenological stages.