Distribution in the Western United States on Alfalfa and Cultivar Reaction to Mixed Populations of Ditylenchus dipsaci and Aphelenchoides ritzemabosi
AbstractDitylenchus dipsaci and Aphelenchoides ritzemabosi were extracted from 29 of 40 plant samples (72.5%) collected from Arizona, California, Colorado, Idaho, Montana, Oregon, South Dakota, Utah, Washington, and Wyoming. Percentages of A. ritzemabosi in tissue of the 29 samples ranged from 1.77 to 67.82%. Only Ditylenchus dipsaci was recovered from the remaining 11 samples. All of the 16 fields sampled in Wyoming contained both nematodes. Percentages of A. ritzemabosi in the Wyoming samples ranged from 0.7-30.0%, with an overall mean of 10.3%. Individual plants collected from a field in Big Horn, Wyoming, all contained both nematodes. Percentages of A. ritzemabosi in tissue ranged from 5-70%. Alfalfa stem nematode symptomatic plants in 17 of 18 alfalfa cultivars collected from a screening nursery in California contained both nematodes, of which 10-94% were A. ritzemabosi. Only one cultivar had D. dipsaci only, and no entries had A. ritzemabosi only. Under environmentally controlled conditions, A. ritzemabosi reproduced in all nine alfalfa cultivars tested at 6 weeks of age with a mean reproductive factor (final population/initial population) of 4.1. There were more (P = 0.05) A. ritzemabosi in stem and bud tissue of the susceptible cultivars at harvest than in the resistant cultivars with combined cultivar means of 238, 42, 78, and 4 A. ritzemabosi/g tissue for the susceptible, moderately resistant, resistant, and highly resistant cultivars, respectively. Percentage A. ritzemabosi in tissues decreased over time in seedlings but increased in older plants. Key words: alfalfa stem nematode, Aphelenchoides ritzemabosi, chrysanthemum nematode, cultivar reaction, Ditylenchus dipsaci, geographic distribution, mixed population, nematode, red clover, Sonchus sp., sow thistle, Trifolium pratense.
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