Effects of temperature and initial inoculation density on root-knot nematode (Meloidogyne incognita) infection ability

The effects of temperature, host vegetables and initial inoculation density of root-knot nematode (Meloidogyne incognita) on root-knot nematode driven vegetable symptoms were investigated under greenhouse conditions. The results showed that the optimum temperature for root-knot nematode incidence from May to September was 22.17~27.61 ℃, with obvious symptom detection in cucumber plants after three days. When temperature was 15.38~18.67 ℃ during January to April and October to December, obvious symptom detection in cucumber plants was after 15 days. Symptom appearance time was delayed and disease incidence inhibited. 15 different host plants were infected by the second-stage juveniles of M. incognita. Symptoms appeared in 10 days for watermelon, melon, bitter-gourd, cucumber, pumpkin, squash and green grocery. There were 5 days later for tomato, cowpea, eggplant cabbage and celery. Symptom appearance time in leek and welsh onion was the longest, without becoming obvious after 30 days. The infection ability of M. incognita varied significantly among the six vegetables (cucumber, tomato, eggplant, green grocery, leek and pepper). The numbers of second-stage M. incognita juveniles in rhizosphere soil and adult females and egg-masses in cucumber and tomato roots were more than those in eggplant, green grocery, leek and pepper. With initial inoculation density enhancement of second-stage juveniles, obvious symptoms appeared earlier in tomatoes with a more severe disease index. When inoculation density of second-stage M. incognita juveniles was 80·100 g^-1(soil), obvious symptoms appeared in tomatoes after four days. At second-stage M. incognita juvenile inoculation rate of 160·100 g^-1(soil), it exceed saturation density thereby suppressing disease rate and index.