Evaluation of Verticillium chlamydosporium and Arthrobotrys oligospora for biological control of Meloidogyne incognita in celery and tomato

Abstract

The ability of nematode trapping fungi and egg-parasitising fungi to colonize and persist in the rhizosphere of crop plants is thought to be an important factor influencing the success of biological control of root infecting nematodes. In this study, two strains of an egg parasitic fungus Verticillium chlamydosporium (Vc- 10 and Vc-2M) and one isolate of the nematode-trapping fungus Arthrobotrys oligospora were evaluated to determine their pathogenicity to Meloidogyne incognita and persistence in the rhizosphere of celery (Apium graveolus L.) and tomato(Lycopersicon esculentum L.) plants in a greenhouse experiment. The isolates tested differed significantly (P≤0.05) in their pathogenicity to M. incognita and survival in the rhizosphere. Isolate Vc-10 of V. chlamydosporium was the most virulent pathogen of the nematode. Root galling was lowest (P≤0.05) in tomato plants treated with the isolate Vc-10 (2.2); pots treated with this isolate had the lowest final soil population of infective juveniles; there was a 62.2% and 98.5% infections of eggs and egg-masses respectively by Vc-10 on tomato plants. Isolates Vc-10 and Vc-2M of V. chlamydosporium persisted in the soil and could be re-isolated from the rhizosphere and roots of tomato plants at least 16 weeks after soil infestation. The final inoculum density was, however, higher (P≤0.05) for Vc-10 (1.35×105 cfu/g soil) than Vc-2M (9.25×104 cfu/g soil). A. oligospora on the other hand did not give any significant (P≤0.05) control of the nematode on both crops, there was severe galling on the roots of celery plants (7.4) and tomato plants (6.3) treated with this biological control agent. A. oligospora could not be re-isolated from the plant rhizosphere sixteen weeks after soil infestation. Lack of nematode control on both crops by A. oligospora was attributed to its poor or no establishment in the plant rhizosphere. The fact that it could not be reisolated from the rhizosphere may imply that the fungus did not survive in the rhizosphere of the test plants.