CONTRIBUTION OF INDIVIDUAL CULMS TO YIELD OF SALT-STRESSED WHEAT

Grain yield in wheat (Triticum aestivum L. emend. Thell.) is highly de pendent upon the number of spike-bearing tilters produced by each plan t. Soil salinity can greatly decrease their number and productivity. K nowing the contribution of specific tillers is essential for breeding salt-tolerant genotypes and for developing wheat growth simulation mod els. Our objective was to determine the effects of soil salinity on th e contribution of individual culms to total grain and dry matter yield s of two spring wheat cultivars, Anza and Yecora Rojo. Plants were gro wn in Pachappa fine sandy loam soil (mixed, thermic, Mollic Haploxeral f) in outdoor lysimeters for 2 yr. Three salinity treatments were impo sed by irrigating with waters containing equal weights of NaCl and CaC l2 (electrical conductivities congruent to 1, 12, or 18 dS m(-1)). Des pite substantial losses in the number of tillers at moderate levels of salt stress, grain yields of the main stem (MS) and tillers T1 and T2 were as great of greater than those on nonstressed plants of both cul tivars. The contribution of the MS to yield on a land area basis incre ased from about 25 to 35% in nonsaline treatments to over 80% with inc reasing salinity. The contribution of primary tillers (congruent to 58 -65% in nonsaline conditions) decreased substantially only at the high est salinity levels. Salinity stress significantly decreased the numbe r of spikelets per spike but the number of kernels per spike either in creased or was unaffected except at the highest level of stress. Incre asing salinity decreased total straw yields primarily because of fewer tillers, but dry weights of the MSs and remaining tillers were also s maller. Results show that loss of spike-bearing tillers accounts for m ost of the yield reduction in salt-stressed wheat.