QTL ANALYSIS OF ABA PRODUCTION IN WHEAT AND MAIZE AND ASSOCIATED PHYSIOLOGICAL TRAITS

Abscisic acid (ABA) is known to affect many aspects of plant growth and development, and stress-induced increases in tissue ABA content are thought to help the plant adapt to the stress. It is, therefore, of interest to identify genes that regulate ABA production in a stressed plant. The possible consequences of allelic variation in these genes can be determined by comparison within genomes of quantitative trait loci (QTL). We have identified genotypes of wheat and maize that differ by up to threefold in ABA accumulation following a drought stress, A population of wheat plants derived from a cross between a high-ABA producer (SQ1, an experimental line) and a low-ABA producer (Chinese Spring, a landrace) has been examined for drought-induced ABA production and genotyped for isozyme and restriction fragment length polymorphic (RFLP) markers. Leaf 4 was tested for drought-induced ABA production in 139 F-2 plants, which gave a range in leaf ABA contents from about 50 to 560 ng/g fresh weight. One-way analysis of variance showed significant association between markers on the long arm of chromosome 5A and a QTL regulating ABA production, the position of which was estimated using the Mapmaker-QTL computer program. An F-2 population of maize plants was characterized with 32 RFLP markers and used to locate genes regulating ABA content in plants growing under drought conditions in a glasshouse. Several other physiological, morphological, and agronomic traits were also measured in these plants, and comparative QTL analysis allowed some possible causal relationships between ABA and other stress-related traits to be tested. The results showed that leaf ABA was more likely to regulate stomatal conductance than xylem ABA, in contrast to the recent findings of others. There was no evidence that ABA had any effect on plant height or developmental rate. The value of this technique for testing the likely roles of ABA in a stressed plant is discussed.