future harv/est - Search CIMMYT repository

A Critique of Breeding Options for the Development of AbioticStress-Tolerant Maize GermplasmS.K Vasal*, S. Pandey. M. Barandiaran, H. CordovaClMMYT-ARMP, P.D. Box 9-188, Bangkok, 10900 ThailandAbstractIn recent years maize breeders have become more aware of the importance of some abioticstresses such as drought and low N. Such traits exhibit genetic variation which can be manipulatedin a variety of ways for affecting improvements. A few of the more important strategies will beclassified as Direct, Indirect, Alternate and Integrated strategies. Direct strategies emphasizeselection directly under specific environments. Indirect strategies, in contrast, involve screening ofelite maize germplasm especially inbreds and hybrids under those specific stresses. The alternatestrategies make use of inbreeding and high densities as a means to reflect improvements in abioticstresses. The integrated strategy uses recurrent selection procedure, and makes use of inbreeding, andhigh densities in different stages of completing a breeding cycle. All strategies will result inimproving the trait(s), however, from the standpoint of resource efficiency and effectiveness, somealternate and indirect strategies may be expected to provide rapid advances. Cyclic improvementprocedures in general will be slow but by emphasizing selection for secondary traits and reducingtime to complete a cycle the progress can be increased. The results from various studies andstrategies wiJl be reported to show progress. Indirect and alternate strategies also helped to identifylines tolerant/resistant to drought or low N which had no previous history of selection for tolerance tosuch traits.IntroductionTolerance to abiotic stresses is important in achieving stability of production in maize. We areaware that abiotic stresses especially drought and low N are of common and widespread occurrence inmany developing countries. The losses from such stresses are unpredictable but could be of varyingmagnitudes depending upon the climatic conditions in any given year. Developing genotypes tolerantto such stresses is complex and difficult. Also in developing stress-tolerant maize genotypes one maychoose one of the several options that are available to the researcher depending upon the resourcesavailable, physical facilities, specific environments for testing and human resource power andscientific strength. It is important to mention that plant breeding objectives can be achieved usingdifferent approaches. Some of the approaches are cumbersome and require long term commjtmentand resources for achieving the desired goals. The other approaches may be simple, problem solvingand limited to testing of elite germplasm at variety, hybrid and inbred line level. This paper willdescribe and discuss various options that can be explored in developing stress-tolerant maizecultivars.Some Concerns in Breeding and Selection of Maize Genotypes Tolerant to Abiotic StressesThe maize plant is interesting as it provides breeders and other researchers a whole range ofoptions in conducting plant breeding business. However, at the same time we should not underestimate that the task of developing maize germplasm tolerant to such abiotic stresses is not easybecause of lack of uniform conditions in the field and difficulties in managing such stresses in aprecise manner. I commonly refer to stress breeding as a big puzzle for reasons that it is complex,difficult and that reasons for superior stress behavior are not well understood. The breeders ingeneral have their own concerns because of trait complexity governed by polygenic system. There is