MADISON, WISCONSIN

University of Wisconsin

 Genetic analysis of tolerance to low-phosphorus stress using RFLPs --Robert Reiter, James Coors, Michael Sussman and Buck Gabelman An understanding of the genetic nature underlying tolerance to low-phosphorus (low-P) stress would permit efficient development of tolerant plant strains. This study was initiated to identify the number of loci in a maize population segregating for tolerance to low-P stress. In addition, the approximate location and magnitude of effect of identified loci were established.

Seventy-seven restriction fragment length polymorphisms (RFLPs) were identified and scored in an F2 population derived from a cross between line NY821 (tolerant) and line H99 (intolerant). The F2 individuals were self-pollinated to produce F3 families. Ninety F3 families were grown in a sand-alumina system that simulated diffusion-limited, low-P soil conditions. The F3 families were evaluated for vegetative growth in two controlled-environment experiments. To identify quantitative trait loci (QTLs) underlying tolerance to low-P stress, the phenotypic performances of the F3 families were contrasted based on genotypic classification at each of the 77 RFLP loci.

Figure 1. Location and R2 values of individual marker loci for total dry weight under P-stress. A highly significant (P<0.01) marker locus is represented by a solid bar, and a significant (P<0.05) marker locus is represented by a hatched bar. Distances, in cM, between marker loci are indicated to the left of each chromosome. Bars lying to the right indicate the alleles with positive effects came from the tolerant parent, NY821. Bars lying to the left indicate the alleles with positive effects came from the intolerant parent, H99.

Six RFLP marker loci, UMC46, UMC42b, UMC138, UMC19, UMC117, and UMC59, were identified as being significantly associated (P<0.01) with some aspect of performance under low-P stress. Four of these loci, UMC46, UMC42b, UMC138, and UMC19, were associated with shoot dry weight under low-P stress. Five loci, UMC46, UMC42b, UMC138, UMC117, and UMC59, were associated with root dry weight under low-P stress. Loci UMC46, UMC42b, UMC138, UMC19, and UMC59 were associated with total dry weight under low-P stress (Fig. 1). One marker locus, UMC138, accounted for 25% of the total phenotypic variation in total dry weight. Additive gene action was predominant for all the QTLs identified. Significant marker loci were located on four separate chromosomes representing five unlinked genomic regions. Two marker loci, UMC42b and UMC138, were significantly associated with an additive by additive epistatic interaction. A multiple regression model including UMC42b, UMC138, and UMC19 and the significant epistatic interaction between UMC42b and UMC138 accounted for 46% of the total phenotypic variation for total dry weight.

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