Indentification of resistance to white mold (stem rot) and Rhizoctonia limb rot in Arachis wild germplasm


University of Georgia

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Southeast (GA, FL, AL)

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Bertioli (S)

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his project started in June 2018. Since then, we have been working on establishing a reliable screening greenhouse/growth chamber method to evaluate Arachis plants for resistance to S. roflsii. The objective of this first part of the study was to find an in vitro based method that would replicate field results reliably. Initially, eight cultivars with known and different levels of field resistance were tested, using the method developed by Renjie Cui (T Brenneman's former MSc student). In summary, plant stems were inoculated with active mycelia of a highly virulent strain of S. rolfsii, growing on a plug of solid medium (Fig2a). This assay was repeated three times with slight variations Fig2b). In all experiments, we were successful in producing infection, but levels were too high, so that little differentiation was observed. Although some cultivars always presented smaller infection length (e.g. Bailey, GA 12Y), there was no statistical significance. We also conducted experiments using inoculum is grown in liquid medium (Bastien et al., 2012). This way, inoculum can be adjusted to an optimum concentration that allows better 

c) Liquid Culture differentiation (Fig2c). Similarly, infection was obtained, but no significant differences between different genotypes. We plan for the next phase of the project, a field experiment with interplanting dense canopy to even out environmental conditions. This experiment will be conducted in the 2019 season. 

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