Management final report covering period, Sep 1, 1987-Sep. 1, 1990 : the development of a drought resistant wheat germplasm

Heat tolerance of wheat materials were studied in growth chamber experiments and in the field. The response of leaf gas exchange to light in different wheat cultivars was studied as means of understanding variations in plant production and the effect of plant selection on productivity and stress adaptation. Mass selection for improved grain filling under post-anthesis stress was performed. The adaptation of wheat to Mediterranean-type drought stress, common to Israel and Portugal, was found to be conditioned primarily by plant phenology. Wheat genotypes of short growth duration have an advantage where total seasonal precipitation is below about 300-400mm. Longer growth duration is advantageous at 600mm or more. Early-maturing genetic materials were developed and are available. Beyond phenology, the most important physiological component in plant adaptation to drought stress was found to be osmotic adjustment. Genetic variation for osmotic adjustment is readily available in the wheat materials studied. Leaf gas exchange and photosynthetic capacity at light saturation was found to be improved in modern high-yielding cultivars which were selected for high yield under the high radiation environment of Israel. Experimental data as combined with theoretical considerations developed by others suggest that the improvement of plant production by way of improved photosynthetic capacity is not possible in all environments and the most likely environment for achieving progress in this respect is a high radiation environment, such as Israel or perhaps southern Portugal. The most prevalent drought stress in wheat in the Mediterranean climate occurs during grain filling. The chemical desiccation of wheat plants after anthesis, as means of revealing genotypic capacity for grain-filling from stem reserves, was used in mass selection to evaluate effectiveness and progress in selection. The method was efficient in increasing grain filling and improving yield of wheat which was practically devoid of any photosynthetic source after anthesis, as the case is for severe drought stress. The method is considered to bc a very simple means of achieving drought tolerance during grain filling without resolving to complex environmental control and laborious procedures of selection. (Author abstract)