Study of the possibility of increasing grain yield by increasing grain weight in winter and facultative wheat genotypes with manipulating sink capacity

Understanding of grain weight potential and determining of how it is affected by manipulating the sink capacity and assimilate supply and possibilities for increasing grain yield is a prerequisite for increasing grain yield in new wheat cultivars. This study was conducted to determine the importance of grain weight as well as assimilates supply, using removal spikelets method, in increasing grain yield in both normal irrigation (NI) and terminal drought stress (TDS) conditions. The experimental design was randomized complete block design (RCBD) with five genotypes at two locations (Karaj and Ardabil) under both NI ans TDS conditions in 2003- 2004 and 2004- 2005 cropping seasons. Grain yield of each bread wheat genotype was measured in both locations in each year. After anthesis stage, 25% and 50% of spikelets of main stem were artificially removed, in each genotype. Results of combined analysis of variance and mean comparisons for grain yield showed that the highest grain yield of 7288 kg ha-1 was obtained from cv. Gaspard with in NI conditions. However, there was not significant differences among cultivars for grain yield in TDS conditions. Results of combined analysis of variance also showed that the effect of genotype and year × location interaction as well as the effect of artificial spikelet removal and year × location × genotype on grain weight were significant at P<0.01 and P<0.05, in NI conditions, respectively, Effect of location and artificial spikelet removal on grain weight were also significant at P<0.01 in TDS conditions. Genotype × artificial spikelet removal interaction on grain weight was not significant at P<0.05. Artificially reducing spikelet numbers by 25% and 50% to increase assimilate supply to the remaining grains increased grain weight by about 13% and 18% in NI conditions, respectively. While, removing spiklets in TDS conditions increased the weight of remaining grains by about 24% as compared to the control (no removal). It is concluded that considerable potential exists for increasing grain weight and as consequences grain yield in winter/facultative wheat genotypes, hence, increasing wheat production in winter/facultative wheat growing areas in Iran.