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Survival of Colletotrichum gloeosporioides (causal agent of yam anthracnose) on yam residues decomposing in soil

Ripoche A., Jacqua G., Bussière F., Guyader S., Sierra J.. 2008. Applied Soil Ecology, 38 (3) : p. 270-278.

Anthracnose, caused by the fungus Colletotrichum gloeosporioides, is the most serious disease affecting water yam (Dioscorea alata) in the tropics. The objective of this study was to determine whether infected yam residues from the previous growing season could be a source of inoculum for the following yam crop. Residue decomposition and survival of the fungus on residues and in the soil were studied in a 161-day field experiment carried out during the dry season in Guadeloupe (French West Indies), which corresponds to the post-harvest period of yam. Artificially inoculated residues (leaves and stems) were put in litterbags, which were then either placed on the soil surface or buried at 0.1 m depth. Residue decomposition was also measured under laboratory conditions to obtain the parameters required by a model of decomposition. Residue decomposition in the field was greater in the first month, then steadily decreased until the end of the experiment. The decomposition rate decreased in the following order: buried leaves > surface leaves > buried stems > surface stems. The model described residue decomposition well, and the simulations showed that soil moisture and residue quality were key factors controlling decomposition in the field. Simulations also indicated that stems may stay more than five months in soil due to the low decomposition rate of the recalcitrant organic fraction. The number of C. gloeosporioides conidia diminished sharply in the first month, and the rate of decrease was similar to that of the labile fraction of residues as estimated by the model. Over this period, the number of conidia was higher in residues placed on the soil surface due to a larger amount of readily available substrate. Later, survival of C. gloeosporioides was mainly limited by the competition with microorganisms decomposing residues. Four months after the beginning of the experiment, 30% of the residues were still present in the field, mainly as stems, and the number of conidia represented less than 1% of the initial amount (e.g. 103¿104 conidia g-1 dry matter). Pathogenicity of yam residues also sharply decreased after the first month and was higher for residues on the soil surface. By the end of the experiment, only stems on the soil surface exhibited pathogenicity. C. gloeosporioides could not be detected either in the soil in contact with the infected residues or in the control soil without residues. Given that the period between harvest and planting is approximately four months, our results indicated that stems on soil surface may contribute to the primary infection of yam with anthracnose.

Thématique : Maladies des plantes; Manutention transport stockage et conservation des produits d'origine végétale

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