Study on Contribution of Basal and Distal Grains of Spikelets to Grain Yield in Winter and Facultative Wheat

Increased grain yield in modern wheat cultivars has been achieved by increasing grain numbers in spike, which has been associated with a greater contribution of the more distal grains (C, D& E) in the wheat spikelet. However, because distal grains are smaller and lighter than basal grains (A and B) they reduce the average grain weight of modern wheat cultivars. The objectives of this study was to determine the contribution of basal (A& B) and distal (C& D) grains formed in various positions on of spikelet on winter and facultative wheat grain yield in terminal drought stress and normal irrigation conditions. The experimental design for both trials was a randomized complete block with three replications. Five winter and facultative wheat genotypes were studied in normal irrigation and terminal drought stress conditions at two locations (Karaj and Ardabil) in 2003-04 and 2004-05 growing seasons. Cv. Gaspard winter wheat had the highest grain yield (7288 kg/ha) under normal irrigation, while the genotypes grown under terminal drought stress conditions had no significant differences in grain yield. Combined analysis of variance showed that the effect of the position of grains was highly significant (P < 0.01) under normal irrigation conditions. Under drought stress conditions, differences due to position of grains was significantly different (P < 0.01), the position of grain × location interaction was also highly significant (P < 0.01), indicating a considerable variation for this character in different environments. All genotypes had significant differences in the weight of grains in the basal (A& B =38 mg), and distal (C & D = 27-32 mg) grains in the spikelets with lighter grains in the C (32 mg) and D (27 mg) grains in spikelets. However, the weight of grains in the A and B position in the spikelets were heavier. The contribution of the basal grains to grain yield was about 28%, while the contribution of C and D grains were about 22.6% and 19.6% respectively, under terminal drought stress conditions. Breading line as C-80-10, which produced heavier basal (40 mg under stress and 48 mg under normal irrigation) and distal grains (33 and 39 mg under stress and irrigation conditions, respectively) are suitable for both emvironments. More physiology- breeding researches are needed for selection of genotypes with larger and uniform grain size for regions prone to terminal drought stress conditions in winter wheat areas of Iran.