Pathogenicity of the burrowing nematode, Radopholus similis on avocado

The pathogenic effect of Radopholus similis on avocado was studied with five different inoculum levels viz. 0, 10, 100, 1000 and 10,000 per plant in 35 cm earthen pots containing sandy loam soil fumigated with methyl bromide. Initial infestation in tender, creamy white fleshy roots produced brown to black coloured lesions. Consequent to multiplication of nematodes these initial lesions enlarged, coalesced which led to rotting. Transverse and longitudinal sections of infested roots showing lesions revealed that R. similis colonised the cortex but not the stelar region. An initial inoculum density of 10,000 nematodes per plant caused 10, 10, 17.46 and 62 per cent reduction over control in length and weight of shoot, number of leaves, weight and volume of root respectively over a period of 4 months. The pathogenic threshold level of R. similis was 100 nematodes per plant or one nematode in 12 cm³ of sandy loam soil for root growth characters. The study has estabilshed the potential of the burrowing nematode as a pathogen of avocado.