PATHOLOGICAL RELATIONSHIP OF MELOIDOGYNE-HAPLA AND PHYTOPHTHORA-MEGASPERMA F SP MEDICAGINIS IN MEDICAGO-SATIVA L - IMPORTANCE OF INOCULATION TIMING, SOIL TEXTURE, AND TEMPERATURE

The effects of inoculation timing, soil texture, and temperature on th e interaction between Meloidogyne hapla and Phytophthora megasperma f. sp. medicaginis were studied on three alfalfa cultivars. Plant surviv al of cultivars 'Deseret' (susceptible to both pathogens) and 'Apollo II' (resistant only to the fungus) decreased, and plant growth was sup pressed compared to uninoculated controls when inoculation with M. hap la preceded inoculation with P. m. f. sp. medicaginis. Survival and gr owth of 'Nev Syn XX' (resistant to both pathogens) were affected littl e or none by any inoculation treatment. Survival of Deseret inoculated with both pathogens was less in clay loam soil than in sandy loam soi l, and shoot growth was suppressed in sandy loam, sandy-clay loam, and clay loam soils. Nematode reproduction and root galling induced by M. hapla were not affected when inoculation with M. hapla preceded inocu lation with the fungus, but increased as a result of preinoculation wi th the fungus. When all three cultivars were inoculated with both path ogens and then grown at 16, 20, 24, and 28 degrees C, the greatest sup pression of shoot growth and the smallest percentage of plants survivi ng occurred on Deseret at 28 degrees C. Growth of Apollo II was less a ffected by temperature than was Deseret, whereas temperature had littl e or no affect on Nev Syn XX.