EAR-STEM RATIOS IN BREEDING POPULATIONS OF WHEAT - SIGNIFICANCE FOR YIELD IMPROVEMENT

Earlier studies showed that the ratio of the weight of the wheat ear t o stem at anthesis (ear:stem ratio) may give a better indication of po tential yield than harvest index because it is determined early in the life cycle and is not affected by post anthesis stress. These studies concluded that selection for high ear:stem ratio at anthesis may lead to further improvement in grain yield of wheat. The present work was undertaken in the field to identify lines varying in ear:stem ratio in breeding populations and to study its implications for yield improvem ent. At anthesis stem length, ear length, tiller number, dry weight of stem and ear and ear:stem ratio were measured in 14 crosses on F-2 Si ngle plants and F-2 derived lines grown in the F-3, F-4, and F-5 at th ree locations in Western Australia over four seasons. In addition, bio mass, grain yield and yield components were measured on selected cross es at two locations on F-2 derived lines grown in the F-4 and F-5 Ther e was a considerable range of ear:stem ratio between and within the cr osses studied. Although ear:stem ratio was strongly correlated with st em length, there was substantial variation within stem length classes. Ear:stem ratio had a high mean broad sense heritability (82%), wherea s HI grain yield and above ground biomass had lower heritabilities, 68 , 55 and 35% respectively. Ear:stem ratio was strongly correlated betw een generations and sites indicating stability of this character. Ear: stem ratio had a significant positive correlation with grain yield, HI , grains per ear and per m(2). The correlation of grain yield with HI was equal or slightly higher than that of grain yield with ear:stem ra tio. Ear:stem ratio offers promise as a predictor of HI and yield pote ntial where post-anthesis moisture stress can influence HI. Ear:stem r atio measurement is unlikely to be adopted for selection purposes in r outine breeding programs, as it is laborious and time consuming. Howev er, ear:stem ratio could be used to identify superior parental genotyp es and early generation selections from special crosses in terms of it s ability to partition assimilate.