CROP PHYSIOLOGY AND BREEDING FOR DROUGHT TOLERANCE - RESEARCH-AND-DEVELOPMENT

This paper presents an example of the research and development function of a physiology group within a cereal breeding program: an evaluation of the possibility of incorporating selection for tolerance to drought stress during the flowering and grain-filling period in pearl millet. It includes a review of the problem and possible solutions, and a report of two experiments conducted to identify phenotypic characteristics associated with yield differences under stress which could be used as selection criteria in breeding for tolerance. Differences among genotypes in yield under stress during flowering and grain-filling were partitioned into differences in yield potential, drought escape, and drought tolerance; the drought response accounted for more than 40% of the observed yield differences. Phenotypic traits related to yield under stress were divided into those reflecting drought escape and those reflecting drought tolerance. Drought tolerance was found to be primarily expressed in traits relating to the ability to maintain grain numbers under stress (grain number per panicle and per unit area, and grain yield per panicle). Drought escape, in contrast, was expressed in terms of greater grain biomass and higher harvest index. However, the field data also indicated that considerable progress in yield under stress should be possible by selection for earlier flowering and improved yield potential alone.