IMPORTANCE OF TEMPERATURE IN THE PATHOLOGY OF MELOIDOGYNE-HAPLA AND M-CHITWOODI ON LEGUMES

Effect 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 Meloidog yne hapla from California (MHCA), Utah (MHUT), and Wyoming (MHWY), and a population of M. chitwoodi from Utah (MCUT). The legumes are milkve tch (astragalus cicer), alfalfa (Medicago sativa), and yellow sweet cl over (Melilotus officinalis). All milkvetch plants survived inoculatio n with all nematode populations, while alfalfa and yellow sweet clover were more susceptible. On yellow sweet clover, MHCA was most pathogen ic at 30 degrees C based on suppression of shoot growth while MHUT, MH WY, and MCUT were most pathogenic at 25 degrees C. All nematode popula tions suppressed growth of yellow sweet clover more than growth of mil kvetch and alfalfa. The reproductive factor (Rf = final nematode popul ation/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 degr ees C and 25 degrees C. The Rf values of MHUT and MHWY were similar on all species and exceeded and Rf of MCUT at all temperature (P < 0.05) .