Comparative Response of Alfalfa to Pratylenchus penetrans Populations.

Four populations of Pratylenchus penetrans did not differ (P > 0.05) in their virulence or reproductive capability on Lahontan alfalfa. There was a negative relationship (r = -0 .7 9 ) between plant survival and nematode inocula densities at 26 +/- 3 C in the greenhouse. All plants survived at an inoculum level (Pi) of 1 nematode/cm(3) soil, whereas survival rates were 50 to 55% at 20 nematodes/cm(3) soil. Alfalfa shoot and root weights were negatively correlated (r = - 0.87; P < 0.05) with nematode inoculum densities. Plant shoot weight reductions ranged from 13 % at Pi 1 nematode/cm(3) soil to 69% for Pi 20 nematodes/cm(3) soil, whereas root weight reductions ranged from 17% for Pi 1 nematode/cm(3) soil to 75% for Pi 20 nematodes/cm(3) soil. Maximum and minimum nematode reproduction (Pf/Pi) for the P. penetrans populations were 26.7 and 6.2 for Pi 1 and 20 nematodes/cm(3) soil, respectively. There were negative correlations between nematode inoculum densities and plant survival (r = 0.84), and soil temperature and plant survival (r = -0 .7 8 ). Nematode reproduction was positively correlated to root weight (r = 0.89).