Breeding wheat for lodging resistance, earliness and tolerance to abiotic stresses

Summary

Wheat yields in Romania show large deviations from the linear regression that describes the trend of increased yields over time, both for the Romanian average and the average of 18 yield trials. The main causes of yield variation that can be reduced by breeding were identified as lodging, drought and heat, and several diseases by correlation analysis and estimation of production losses. The introduction of the Rht1 gene improved lodging resistance, but its effect on yield varied from −23 to +29%, with an average of +4.9% in the southern and western regions, and +0.3% in the central and eastern regions of the country. Improvement in emergence, drought and heat tolerance and disease resistance should improve the average effect of Rht genes. Selection for grain appearance helped improve heat tolerance, and further progress is foreseen by exploiting the large variation found in membrane thermostability. Differences in drought susceptibility index were correlated with yield without stress, while deviations from linear regression on potential yield were correlated with water loss from excised leaves. Early maturing wheat, which can escape heat and drought, was found to have unstable yields because of sterility following exposure to low non-freezing temperatures during meiosis. Therefore, breeding for earliness has to be associated with selection for tolerance to such low temperatures.