KERNEL WEIGHT RESPONSE TO SOURCE SINK CHANGES IN SPRING WHEAT

Field trials were used to investigate the hypothesis that yield of some cultivars of spring wheat (Triticum aestivum L.) may be limited by potential seed size. Eight cultivars, varying in kernel weight from 32 to 46 mg were tested in replicated experiments under dryland growing conditions at Saskatoon in 1985 and 1986. Plot thinning at the six-leaf stage or at heading was used to increase the supply of photosynthate to developing spikes. Spikelet reduction, by severing spikes between spikelets 10 and 11 at anthesis or 8 or 18 d after anthesis, was used to increase the supply of photosynthate to the remaining spikelets. Flag leaf blade removal at anthesis or 8 or 18 d after anthesis was used to reduce the supply of photosynthate to developing kernels. Significant interaction between cultivar and spikelet reduction treatment in both years indicated that some cultivars were limited in kernel weight because of limited sink size. It was not clear whether greater sink capacity was associated with larger kernels or with semidwarf stature. Yield limitations due to sink capacity are expected to occur rarely under dryland growing conditions.