Banana root rot disease caused by Cylindrocladium sp. as related to soil type

In the carribean islands, bananas are cropped on a large variety of soils, distributed according to chrono-topo-climo-sequences. Under intensive monoculture, Vertisols sustain constant yielding crops while Andosols derived from recent ash deposits are associated with yield depletion caused by root damage due to nematodes and the fungus #Cylindrocladium# sp. This paper is aimed at assessing the relationship between soil type and the banana root disease caused by the fungus. A field survey shows that banana root damage is closely related to soil type and weathering stage. The severity in root injury increases with decreasing clay and free Fe, Mn content. A Mn deficiency in banana plants cropped on the Andosols, may possibly influence the banana root tolerance to fungal infection. The weakest root damage occur in the Vertisols. The soil inoculum density of #Cylindrocladium# sp. ranges from 0-4 to 8-37 UFC/g soil in Vertisols and Andosols respectively. Soil receptivity to #Cylindrocladium# sp. is measured in both sterilized and unsterilized conditions in the Ap horizons of three distinct soils : Andosol, Vertisol and Nitisol. The dominant clay minerals in the Vertisol and Nitisol (>70% clay) are smectite and halloysite respectively. In unsterilized conditions, results show that a given damage intensity of 40-60 % injured root surface involves an inoculum density of #Cylindrocladium# sp. amounting to 2 and 20 UFC/ml soil in the Andosol and Vertisol respectively. These soils are respectively strongly and weakly conducive for the banana root disease induced by #Cylindrocladium# sp.; while the Nitisol represents an intermediate situation. relatively to unsterilized conditions, root damage increases in sterilized conditions whatever the inoculum level and similar differences in receptivity are observed between the distinct soils. Abiotic soil factors therefore act on soil receptivity to #Cylindrocladium# sp.