Differential Pathogenicity of Four Pratylenchus neglectus Populations on Alfalfa
A Pratylenchus neglectus population from lltah (UT3) was more virulent to Lahontan alfalfa than other P. neglectus populations from Utah (UT1, UT2) and Wyoming (WY). All alfalfa plants survived at 24 ± 3 C when inoculated with WY, UT1, or UT2 at initial populations (Pi) of 500, 1,000, and 5,000 nematodes per plant. At Pi 10,000 with WY, UT1, or UT2, plant mortality was 15, 15, and 20%, respectively; at Pi 5,000 and 10,000 with UT3, plant mortality was 10 and 40%. The WY, UT1, and UT2 populations reduced (P = 0.05) root growth at Pi 10,000 only, and UT3 reduced (P = 0.05) root growth at Pi 1,000, 5,000, and 10,000. At Pi 5,000, shoot dry weights were reduced by 10-23% by WY, 14-29% by UT1, 12-25% by UT2, and 20-48% by UT3 at 15-30 C. The UT3 population reduced (P = 0.05) root dry weight at 20-30 C at Pi 1,000 and 5,000. The WY, UT1, and UT-2 populations did not reduce (P = 0.05) root growth at any temperature or Pi. The UT3 nematode reproductive indices were greater than those of the other nematode populations at all Pi and increased with temperature. Key words: alfalfa, Lahontan, Medicago sativa, nematode, plant survival, Pratylenchus neglectus, reproduction, temperature, virulence.