Abstract
Sweet potato (Ipomoea batatas) tuberous roots are used for human consumption, animal feed, and many industrial products. However, the crop is susceptible to various pests and diseases, including foot rot disease caused by the phytopathogenic fungus Plenodomus destruens. Biological control of plant pathogens by Bacillus species is widely disseminated in agrosystems, but specific biological control agents against the foot rot disease-causing fungus are not yet available. Our previous studies showed that two Bacillus strains isolated from sweet potato roots—B. safensis T052-76 and B. velezensis T149-19—were able to inhibit P. destruens in vitro, but data from in vivo experiments using simultaneously the fungus and the bacteria were missing. In this study, both strains were shown to protect the plant from the disease and to mitigate the symptoms of foot rot disease in pot experiments. Total fungal community quantification using real-time PCR showed a significant decrease in the number of copies of the ITS gene when the bacteria were inoculated, compared to the control (with the fungus only). To determine the genes encoding antimicrobial substances likely to inhibit the fungus, their genomes were sequenced and annotated. Genes coding for mycosubtilin, bacillaene, macrolactin, bacillibactin, bacilysin, plantazolicin, plipastatin, dificidine, fengycin and surfactin were found in B. velezensis T149-19, while those coding for bacylisin, lichenysin, bacillibactin, fengycin and surfactin were found in B. safensis T052-76. Altogether, the data presented here contribute to advancing the knowledge for the use of these Bacillus strains as biocontrol products in sweet potato.
Highlights
Sweet potato (Ipomoea batatas (L.) Lam.) belongs to the family Convolvulaceae and is among the most widely cultivated subsistence crops worldwide, with more than 100 million tons per year [1]
Data obtained from in vivo experiments using simultaneously the fungus and one or two bacteria (B. safensis T052-76 and B. velezensis T149-19) were still missing. Based on these promising results for biological control in sweet potato, this study aims to determine whether these Bacillus strains are able to inhibit P. destruens and prevent the appearance of foot rot symptoms in pot experiments
The genome of B. velezensis T149-19 was estimated at 3,894,256 bp in length, totaling 75 contigs, and a GC content of 46.5%
Summary
Sweet potato (Ipomoea batatas (L.) Lam.) belongs to the family Convolvulaceae and is among the most widely cultivated subsistence crops worldwide, with more than 100 million tons per year [1]. Sweet potato can be produced under unfavorable growing conditions and with low production cost, some diseases and pests severely affect its cultivation. Most pathogens cause damage to the roots, causing a strong reduction or even total loss of production [8,9]. The bacterial pathogens Erwinia chrysanthemi and E. carotovora are the most important phytopathogens of sweet potatoes worldwide [10]. Pathogenic fungi are responsible for the greatest economic losses in sweet potato cultivation [9]. Ceratocystis fimbriata, Fusarium oxysporum, Rhizopus oryzae, and Monilochaetes infuscans are some examples of fungi that cause different diseases in sweet potato. Jiang et al [11] have demonstrated the potential of Pantoea dispersa as an effective biocontrol agent for black rot in sweet potato caused by C. fimbriata. The most feared by farmers, mainly in tropical countries, is the fungus Plenodomus destruens, which causes foot rot disease [9,12]
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