EVALUATION OF CHEMICAL DESICCATION AS A SELECTION TECHNIQUE FOR DROUGHT RESISTANCE IN A DRYLAND WHEAT BREEDING PROGRAM

Previous studies have shown that some chemical desiccants and senescin g agents, when applied to adequately watered cereals 10 to 14 days aft er anthesis, can be used to select lines with stable grain size (kerne l weight) under post-anthesis water deficits. The present study evalua ted the potential of one of these chemicals, potassium iodide (KI), to select for this character in a dryland wheat breeding program. Ninety -six F2-derived lines grown in the F6 and F7 generations and 11 cultiv ars of wheat (Triticum aestivum L.) were grown in two experiments at t wo medium-rainfall sites in 1988 and 1989 and sprayed with a 0.3% solu tion of KI when the grains had developed one-third in the lemma. Reduc tions in grain yield and thousand kernel weight due to treatment with KI were greater in 1988 than in 1989, probably due to the higher growi ng-season rainfall in that year. -The reduction in grain yield as a re sult of desiccation was greater than the reduction in thousand kernel weight, but the correlation between the two was low (0.09 to 0.58) and non-significant in five out of the eight comparisons. There were cons iderable differences among genotypes in response to the desiccation tr eatment in the wetter 1988. Genetic coefficients of variation ranged f rom 5.6 to 12.9% for yield and 2.5 to 9.5% for thousand kernel weight. The ratio of the variance component estimates for the interaction bet ween genotypes and desiccation treatment to the variance component est imates for genotypes was generally less than one. However, genetic dif ferences in response to the desiccation treatment could be demonstrate d in some experiments, particularly at one site and in the wetter of t he two years. We conclude that the chemical desiccation technique can be used to select for post-anthesis drought resistance in a dryland br eeding program. However, there are some limitations to the technique, and selection needs to be confined to wetter sites and seasons.