never been rated for Al tolerance (Palmer et al., 1996). The few soybean germplasm evaluations to date indicate Screening methodology remains a practical barrier in the breeding that soybean can be screened for tolerance to Al-rich of Al-tolerant soybean [Glycine max (L.) Merr.]. Our objectives were to (i) develop a repeatable sand-media culture method for Al toler-acid soil with some degree of success (Sartain and Kamance screening of plants, (ii) compare Al response of genotypes in prath, 1978;Hanson and Kamprath, 1979; Campbell and sand culture to a standard hydroponics-based seedling culture, and Horst and Klotz, 1990;Foy et al., 1992, (iii) establish a practical guide for the use of hydroponics and sand-1993b; Spehar, 1994). However, genotypic rankings for culture screening methods in the selection of Al-tolerant soybean. We Al tolerance often vary among soil types. developed a sand-media culture method and imposed 0 and 450 M Aluminum saturation, the percentage of cation-ex-Al 3؉ activity treatments upon 10 diverse soybean genotypes. The exchange capacity occupied by Al, has been employed in periment employed a randomized complete block design with nine recent decades to classify the potential for Al toxicity replications. Root weight and relative root surface area (RRSA) were in soils, but it has not helped soybean breeders to predict determined at 18 d after transplanting (DAT). In hydroponics, the changes in genotypic rankings for Al tolerance that may genotypes were compared for taproot elongation after 3 d of exposure to 0, 2, and 5 M Al 3؉ activity treatments in a split plot design with occur from one soil type to the next (Kamprath, 1984; six replications. Aluminum stress was imposed successfully (approxi-Fageria et al., 1988). Researchers have attributed dismately 57% of the growth in control) in hydroponics and sand culture, crepancies in genotype rankings to the different concenbut discrepancies between methods were apparent. The hydroponicstrations of Al, P, Ca, Mg, organic acids, and other soil based seedling screen produced an inflated range of genotypic response components which greatly affect and potentially mask and altered Al tolerance rankings in comparison with sand culture.

Samples of perithecia of Blumeria graminis f. sp. tritici from senescing wheat leaves were collected by cooperators from 17 states. Ascospores were discharged from perithecia and single-spore isolates were characterized for virulence genes using a differential host series containing 15 known resistance genes. A total of 520 isolates from 17 states were characterized in 1993 and 1994. Virulence frequencies and complexity and racial composition were examined. The data were analyzed for associations among sets of virulence genes and the geographical distribution of phenotypes. Virulence to Pm3c, Pm3f, pm5, Pm6, and Pm7 was present in all states surveyed. Since 1990, virulence to Pm3a has increased in the northeast, and virulence to Pm1, Pm4b, Pm8, and Pm17 has increased across the area surveyed. The resistance genes Pm12 and Pm16 remain highly effective in the southeastern United States. An increase in virulence frequencies and complexity of isolates was observed.

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