Microbial disease complex of sweetpotato (Ipomoea batatas L. Lam.) tip/end rot
C. E. STOKES (1), R. A. Arancibia (1), R. E. Baird (1). (1) Mississippi State University, Mississippi State, MS, U.S.A.
A two year study was conducted to determine the causal agent(s) responsible for a severe outbreak of sweetpotato tip/end rot in north Mississippi. Microbes were sampled from plant tissues over eight production stages. Identifications were confirmed for all isolated bacteria and fungi using 16S and ITS sequence data, respectively. Three bacteria, <i>Bacillus</i> spp., <i>Lysobacter enzymogenes</i>, and <i>Paenibacillus lentimorbus</i>, occurred across the eight production stages, but 30 additional taxa were also identified. None were found to be pathogenic when screened. However, a number of fungi, <i>Macrophomina phaseolina</i>, <i>Aspergillus flavus</i>, <i>A. niger</i>, <i>A. tubingens</i>, <i>A. japonicas</i>, and six species of <i>Fusarium</i>, were pathogenic in trials. In addition, <i>F. oxysporum</i> and <i>F. solani</i> consistently produced necrotic lesions in root tissue. These two species accounted for nearly 70% of the overall isolates from early season seed stock and bedding plant samples. Microbial populations in post-harvest tissues differed in relative abundance from prior sampling dates. <i>Macrophomina phaseolina</i> increased to 6.5% occurrence and <i>F. oxysporum</i> and <i>F. solani</i> decreased to 27% isolation frequencies between 60 and 90 days post-harvest. To overcome selective media biases, Illumina whole-community sequence data is being generated from tissue samples used in microbial isolation. Fungal occurrence and population data will be evaluated within and across production stages.
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