Pathogenicity of the Lesion Nematode, Pratylenchus brachyurus, on Six Soybean Cultivars.

Pathogenicity tests of Pratylenchus brachyurus on selected greenhouse-grown soybean cultivars indicated the nematode reduced seed yield of 'Hood' but not that of 'Custer', 'Bragg', 'Dyer', or 'Pickett'. Root weights of all cultivars were reduced. Damage and numbers of nematodes within soybean roots growing at 13, 21, and 29 C were greater at higher temperatures. At 29 C, root pruning was prominent in 'Hood' and 'Pickett' but limited in 'Custer' and 'Hill'. Root pruning was not observed at 13 C and only 'Pickett' showed pruning at 21 C. Plant height and foliage weight were not affected. P. brachyurus had no effect on the emergence of 'Pickett' or 'Bragg' soybeans. Nematode counts from roots of 'Pickett' at intervals after inoculation indicated that hatching of second generation second-stage larvae occurred about 15 days after egg laying. An average of 68% of the initial inoculum penetrated the roots within five days of inoculation, the highest observed was 81% in five days. Details of structural damage in penetrated tissues were studied in sectioned roots. In soybean roots infected by P. brachyurus and/or Rhizoctonia solani greater damage occurred with nematode and fungus combined than with either acting alone.