QTL analysis of drought-related traits and grain yield in relation to genetic variation for leaf abscisic acid concentration in field-grown maize

Abstract

deficit (Zeevaart and Creelman, 1988; Bray, 1997). ABA modulates the expression of a large number of genes Abscisic acid (ABA) concentration is a quantitatively whose products may protect the cell from the harmful inherited trait which plays a pivotal role in the eVects of an excessive water loss (Bray, 1993; Close, 1996, response of plants to drought stress. A recent study 1997; Ingram and Bartels, 1996). It has been hypothesized identified 17 quantitative trait loci (QTLs) controlling that ABA may be involved in controlling leaf expansion bulk-leaf ABA concentration (L-ABA) in a maize (Zea during water deficit via modulation of cell wall-associated mays L.) population of 80 F 4 random families tested peroxidase activity (Bacon et al., 1997). Under conditions for two years under droughted field conditions. Sixteen of water deficit, an increased ABA concentration has also of the QTL regions influencing L-ABA also harboured been shown to increase the root to shoot ratio (Sharp, QTLs for one or more of the following traits: stomatal 1996), another important trait influencing drought tolerconductance, a drought sensitivity index, leaf temper- ance. The adaptive role of an increased ABA concentraature, leaf relative water content, anthesis-silking tion is well represented by the consequent reduction in interval, and grain yield. The analysis of the effects of stomatal conductance and in water lost by transpiration each QTL region on the investigated traits indicated ( Trejo et al., 1995). Even though it has been shown that that L-ABA mainly represented an indicator of the level ABA in the xylem sap more tightly controls stomatal of drought stress experienced by the plant at the time conductance than ABA in the bulk-leaf tissue (Davies of sampling because an increase in L-ABA was most and Zhang, 1991; Tardieu et al., 1992, 1993; Jackson, commonly associated with a decrease in both stomatal 1993), the diYculty in collecting a large number of conductance and grain yield as well as an increase in samples of xylem sap has led many authors to focus on leaf temperature. Opposite results were observed at bulk-leaf ABA concentration (L-ABA). one QTL region on chromosome 7 near the RFLP locus Although the above-mentioned findings clearly indicate asg8. A model is presented to interpret these con- a positive role of ABA in increasing plant survival under trasting results in terms of pleiotropic effects. drought, it remains diYcult to predict the global eVect which genetic variation in L-ABA may have on crop