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Infection of Sweetpotato by Fusarium solani and Macrophomina phaseolina Prior to Harvest

The end rot disease complex, caused mainly by Fusarium solani and Macrophomina phaseolina, can be an important postharvest problem in sweetpotato. The disease develops a few weeks after storage roots are harvested and stored. Isolations attempted after harvest showed that the pathogens can be present inside the storage roots before symptoms appear. To determine how and when end rot pathogens enter sweetpotato storage roots, two greenhouse experiments were designed using tissue culture-derived plants free of F. solani and M. phaseolina. In one experiment, plants were grown in autoclaved soil, and 1 month after transplanting, plants were inoculated at the soil line with either noninfested toothpicks or toothpicks infested with each fungus alone or combined. In the other experiment, plants were grown in noninfested soil or in soil infested with each fungus alone or combined. F. solani and M. phaseolina were isolated from roots, storage roots, and plant stems below the soil line, at the soil line, and 5 cm above the soil line in both experiments. This suggests these fungi are capable of invading sweetpotato plants and storage roots from infested soil, and can systemically colonize the plant from infected plant propagation material.