TILLER MORTALITY AND ITS RELATIONSHIP TO GRAIN-YIELD IN SPRING WHEAT

Spikeless tillers of wheat (Triticum aestivum L.) affect grain yield b ecause of less than optimum effective plant population. This study was conducted io examine the genetic variability for tiller mortality, an d its relationship to grain yield in diverse wheat lines. Twenty lines were evaluated in replicated field tests in 4 years at Rampur, Nepal. The characters investigated were maximum number of tiller produced, t he number of reproductive tillers, tiller mortality, and grain yield. The lines differed significantly for all characters. The tiller mortal ity ranged from 7 to 30%. There were substantial effects of environmen t on all four characters. The entry-by-year interactions were signific ant for all traits, primarily because of changes in the relative genot ypic differences for these traits in the four years. However, certain lines consistently ranked low or high for tiller mortality. There was a significant negative correlation between tiller mortality and grain yield in 3 out of 4 years. There was a positive correlation of highest tiller number with reproductive tiller number and with tiller mortali ty. Grain yield showed a nonsignificant positive correlation with maxi mum tiller number. The reproductive tiller number was positively corre lated with grain yield. Results of this study indicate that spikeless tillers contribute negatively to grain yield and that genetic variatio n exists for tiller mortality in spring wheat.