per locus, 53.3% polymorphic loci, and the amount of among-population genetic variation was much smaller Red clover (Trifolium pratense L.) is a forage legume with considthan the within-population variation. The objective of erable economic importance in world agriculture. Knowledge of the this study was to assess genetic diversity in North Ameriamount and distribution of genetic variability within a species is vital to breeders and geneticists when selecting breeding germplasm. The can red clover cultivars on the basis of isozyme data.objectives of this study were to assess genetic diversity in 34 North American red clover cultivars by means of isozymes. Isozymes assayed MATERIALS AND METHODS were esterase, ␤-glucosidase, phosphoglucomutase, peroxidase, di-Seeds of 34 red clover cultivars (Table 1) were obtained aphorase, phosphoglucoisomerase, and superoxide dismutase. Eleven from the USDA-ARS Plant Introduction Stations at Pullman of the 13 loci (84.62%) were polymorphic in at least one cultivar. (W-6), WA, and Griffin (S-9), GA. Eighteen plants of each Percentage polymorphic loci within cultivar ranged from 61.54% in accession were grown in pots filled with potting soil in a greencv Morred, Persist, and Redland II to 84.62% in cv Arlington, Ram, house. and Red Baron, with an overall mean of 73.98%. At the species level,

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Silver reflective plastic mulches were compared with conventional bare-ground culture of yellow crookneck summer squash (Cucurbita pepo L. var. melopepo Alef.) for reducing aphids and the following mosaic virus diseases: cucumber mosaic, watermelon mosaic I and II, zucchini yellows mosaic, and squash mosaic. Plants grown on silver plastic mulch produced higher marketable yields than those grown on bare ground. Other colors (white, yellow, and black with yellow edges) of plastic mulch were intermediate in their effects on aphid population and virus disease reduction. Silver reflective mulch alone and silver reflective mulch with insecticide were superior to other colors of plastic mulch in reducing aphid populations. Silver reflective plastic mulch, with or without insecticide, resulted in 10 to 13 days delay in the onset of the mosaic diseases noted.