Importance of Temperature in the Pathology of Meloidogyne hapla and M. chitwoodi on Legumes.

Effects of temperatures on the host-parasite relationships were studied for three legume species and four populations of root-knot nematodes from the western United States. The nematode populations were Meloidogyne hapla from California (MHCA), Utah (MHUT), and Wyoming (MHWY), and a population of M. chitwoodi from Utah (MCUT). The legumes were milkvetch (Astragalus cicer), alfalfa (Medicago sativa), and yellow sweet clover (Melilotus officinalis). All milkvetch plants survived inoculation with all nematode populations, while alfalfa and yellow sweet clover were more susceptible. On yellow sweet clover, MHCA was most pathogenic at 30 degrees C based on suppression of shoot growth while MHUT, MHWY, and MCUT were most pathogenic at 25 degrees C. All nematode populations suppressed growth of yellow sweet clover more than growth of milkvetch and alfalfa. The reproductive factor (Rf = final nematode population/initial nematode population) of MHCA was positively correlated (r = 0.83) with temperature between 15 degrees C and 30 degrees C. The greatest Rf occurred on alfalfa inoculated with MHCA at 30 degrees C. The Rf of MHUT, MHWY, and MCUT were positively correlated (r= 0.76, r= 0.78, and r= 0.73, respectively) with temperature between 15 degrees C and 25 degrees C. The Rf values of MHUT and MHWY were similar on all species and exceeded the Rf of MCUT at all temperatures (P < 0.05).