LEAF AND SPIKELET PRIMORDIA INITIATION IN SALT-STRESSED WHEAT

Salt stress is known to affect adversely shoot apex development in cereals. This study was conducted to determine rate and duration of leaf and spikelet primordia initiation as related to final leaf and spikelet numbers in salt-stressed wheat (Triticum aestivum L.). Early shoot development of two hard red spring wheat cultivars, Yecora Rojo and Anza, was studied in both greenhouse sand cultures and outdoor field lysimeters. In each case, two saline treatments were compared with a nonsaline control treatment. The sand cultures were irrigated with complete nutrient solutions to which NaCl and CaCl2 (2:1 molar ratio) were added to achieve electrical conductivities (kappa(iw)) of 1.7, 12.2, and 15.1 dS m(-1). Lysimeters were irrigated with tap water salinized to kappa(iw) levels of 0.8, 11.4, and 17.1 dS m(-1). Timing of primordium initiation was expressed in accumulated thermal time measured in the soil (degrees C d(soil)). A three-piece linear-spline model was developed to facilitate the statistical analysis and interpretation of primordium initiation. Parameters of the model corresponded to morphologically significant events. In both experimental locations, each genotype exhibited a similar response to increasing salinity. The rate of leaf primordium initiation decreased while the duration of this phase was unchanged. Salinity had no effect on the rate of spikelet primordium initiation of the genotypes, but the duration of this phase was shortened. As a result, the number of leaves on the main stem and the number of spikelets per spike were significantly reduced by salinity and the yield potential of both genotypes was severely limited.