GENOTYPE AND N RATES EFFECT ON DRY MATTER ACCUMULATION AND MOBILIZATION IN WHEAT (TRITICUM AESTIVUM L.) IN SUB TROPICAL CONDITIONS

In wheat, the supply of assimilate to grain originates from current assimilation transferred directly to kernels and from the remobilization of assimilates stored temporarily in vegetative plant parts. The field experiments were conducted at the experimental farm of Faculty of Shahid Chamran University of Ahvaz, Iran, during 2008-2009 growing seasons. Experimental design was split-plot, N rates as main plots and wheat cultivars as sub-plots. Different stem and internode weight and length, their effects and relationships among stem segments and dry matter accumulation and mobilization were measured at 10-d intervals in 4 old and modern wheat cultivars grown under different N rates. Our results showed that, the main effect of genotype, nitrogen rate and interaction of GIN were significant. Internode length, weight, and specific weight were increased with N application. Mobilized dry matter was more in no N application than in high N application for peduncle (157 vs. 113 mg), penultimate (200 vs. 140 mg) and the lower internodes (329 vs. 190 mg). High N application decreased mobilization efficiency, expressed as percentage of maximum dry mater mobilized, in the peduncle, penultimate, and the lower internodes by 28, 19, and 35%, respectively. Therefore, partitioning of stem reserves into different internodes and their specific weights, play a key role in differences between old and modem wheat cultivars for accumulation and mobilization of dry matters. In general, the old cultivar Chenab and modem cultivar Dena showed relatively the greatest rate and extent of dry matter accumulation and subsequent mobilization in main stem. Genotypes with greater rates of dry matter accumulation and mobilization are exposed less to depressing effect of nitrogen deficiency than those with lower rates. Dry matter mobilized from all three segments of main stem in all genotypes examined in this trial increased in response to no application of N.