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Potential sources of inoculum and survival of Macrophomina phaseolina in Florida strawberry fields

Juliana Baggio: GCREC - University of Florida

<div><em>Macrophomina phaseolina</em>, the causal agent of charcoal rot, affects strawberry crowns inducing plant collapse. The fungus survives in the soil through resistant structures (microsclerotia) and is usually controlled by pre-plant fumigation of soil. However, in the 2016-17 Florida strawberry season, roughly 20% plant mortality still occurred due to charcoal rot where plastic-covered beds were re-used for a second season and crop residue (old strawberry crowns/roots) were disposed between beds. Crowns from the previous season were collected from three farms where charcoal rot was reported and <em>M. phaseolina</em> was recovered from all samples. After the season, infected crowns were buried in the soil and retrieved every two weeks for three months to quantify survival of <em>M. phaseolina</em>. No reduction in the frequency of fungal recovery from crowns was observed during this period. To test the ability of infected crop residue to serve as a source of inoculum for healthy plants, infected crowns were disposed of in the bed alleys or buried next to new plantings of ‘Festival’, ‘Florida Beauty’ and ‘Winterstar’. After 12 weeks, respective average plant mortality for the three cultivars was 60, 43 and 83% when crowns were placed in the bed alleys, and 53, 30 and 63% when crowns were buried in the beds. Our results suggest that <em>M. phaseolina</em> survives over summer in Florida on old strawberry crowns that do not decompose and may act as source of inoculum for healthy plants.</div>