Variation in Resistance of Soybean Lines to Races of Heterodera glycines
AbstractThe objective of this study was to determine the interrelationships of Heterodera glycines races based on their resistance to soybean (Glycine max) cultivars and lines against which they were tested. Greenhouse tests determined the numbers of females of each of eight races of H. glycines that developed on 277 to 522 soybean cultivars and lines. A Female Index (number of females on a test cultivar as a percentage of the number on 'Lee 74') was calculated and used in frequency distributions, correlations, and duster analyses of the resistance reactions to the different races in an attempt to determine relationships among cultivars. Frequency distribution patterns of all cultivars and lines tested against each race were skewed in favor of resistance, and in some cases bimodality was observed. The majority of correlations between pairs of races were highly significant. Cluster analyses based on the correlations divided eight races into four clusters that explained 73% of the variation in resistance. Cluster 1 was comprised of races 2, 4, and 14; Cluster 2 was comprised of races 6 and 9; Cluster 3 was comprised of races 1 and 3; and Cluster 4 was comprised of race 5. The information obtained in this study could increase the efficiency of testing resistant soybean breeding lines for resistance to H. glycines. Key words: Cluster analysis, Glycine max, Heterodera glycines, nematode, resistance, soybean, soybean cyst nematode, virulence group.
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