In a 139-day greenhouse experiment at 24 3C, Pratylenchus penetrans populations from alfalfa in southern (PP1) and central Utah (PP2) were more virulent to 'Lahontan' alfalfa than were P neglectus populations from alfalfa in northern (PN1) and central Utah (PN2). PP1 and PP2 did not differ in virulence or reproduction, but PN1 was more virulent and had a higher reproductive index than PN2. For all populations, there were negative correlations between inoculum density and dry shoot weight, as well as between inoculum density and dry root weight. There were positive correlations between root growth and nematode reproduction. In environmental growth chambers at constant temperatures of 15, 20, 25, and 30C, differences between the effects of the populations on alfalfa in growth chambers at all temperatures were generally similar to those observed in the greenhouse. However, the optimum temperature for alfalfa growth was near 25C whereas the optimum temperature for nematode reproduction a
