Pathogenicity of fungi associated with yam rot disease of Dioscorea alata and their effect on tuber quality

Abstract

Many pathogens have been reported to be associated with tuber rots of yam. These reduce the yield and economic value of the crop. A diagnostic probe, including visual and microscopy parameters, was carried out to determine the pathogenicity of fungi associated with tuber rot in Dioscorea alata and their effect on yam nutritive value. Thirty-two yam tubers were obtained from the International Institute of Tropical Agriculture (IITA) yam barn in Ibadan. Yam tubers showing various symptoms were selected, and pieces of the diseased portion were taken for isolation using standard procedures. The pathogenicity of the fungal isolates was tested using a tuber inoculation assay. Aspergillus niger, Aspergillus flavus, Rhizopus stolonifer, and lasiodiplodia theobromae were isolated from rotted yam and they were found to be pathogenic on yam. Aspergillus niger and Lasiodiplodia theobromae were the most pathogenic among the fungi isolates with 49.91 % and 38.2 % tot severity respectively. The proximate analysis result showed an appreciable reduction in the nutritional composition of infected water yam. The percentage of dry matter composition (88.39 %) was lowest in yam tuber infected by Rhizopus sp., this was followed by yam tuber infected by Aspergillus niger. A. niger and L. theobromae also affected the quality and nutrient composition of yam. The study highlights the significant impact of fungal pathogens on tuber rot in Dioscorea alata (water yam), with Aspergillus niger and Lasiodiplodia theobromar being the most pathogenic. This study showed that these fungi are not only responsible for rot in yam tubers but can also cause a significant decrease in the nutritional composition and quality of yam tubers. Therefore, understanding the impact of these pathogens is crucial for developing effective management strategies to protect crop yield and economic value.