Effect of the root-knot nematode, Meloidogyne incognita, on incidence of the damping off in cucumber seedlings

Abstract

Control effect against the damping off in cucumber seedlings grown in the soil infested with M. incognita was significantly high in the treatments with the volatile chemicals, chloropicrin, NCS, D-D, DBCP; the organic insecticide, Methomyl (Lannate); and the selective fungicides, DAPA (Dexon) or Hymexazol (Tachigaren). However the treatments with other selective fungicides, Benomyl (Benlate) or PCNB resulted in accelerative incidence of the damping off in seedlings. Among several isolates taken from the disease materials, five isolates of Pythium spp. including P. aphanidermatum (Isolate-A, Isolate-B), P. debar yanum, P. spinosum and P. sp. were the dominant group compared with other fungi, Fusarium spp. or Rhizoctonia solani. Incidence of the damping off in seedlings inoculated with each fungal isolate and the nematode increased rapidly in plots of the inoculation containing Pythium spp. and M. incognita. In some inoculation studies on P. aphanidermatum and M. incognita, the influence of root-knot nematode on the damping off development varied with the fungal inoculation level and the growing stage of seedlings. Particularly, at the seeding stage when seedlings have high susceptibility to the fungus, the disease severely occurred in seedlings inoculated with the fungus and the nematode simultaneously, but at a later stage, 7 or 14 days after seeding, the heavier disease development appeared in seedlings inoculated with the root-knot nematode 7 or 14 days before the fungus inoculation than in those inoculated with both pathogens simultaneously. It was observed that infection of P. aphanidermatum zoospores in cucumber roots on agar plate was more rapid among the roots invaded by the root-knot nematode.