Graduate Research and Discovery Symposium (GRADS)

Document Type


Publication Date

Spring 2015


Alternaria rot, caused by Alternaria alternata, was observed in well managed, commercial peach orchards in South Carolina. In total, 64 isolates were collected in 2012 and 2013 from symptomatic fruit of problem orchards. Most isolates were resistant to boscalid, pyraclostrobin, and thiophanate-methyl. Resistance to SDHIs was due to point mutations in the SDH subunits, resistance to pyraclostrobin was due to the G143A mutation in the cytb gene, and resistance to thiophanate-methyl was due to 167Y in the β-tubulin gene. The four most commonly found genotypes based on mutations in the SDH subunits (H277Y in SDHB, H134R in SDHC, D123E in SDHD) were selected for fitness evaluations. Genotypes H277Y and H134R didn’t suffer fitness penalties based on mycelia growth on PDA, spore production in vitro, osmotic sensitivity, oxidative sensitivity, germination ability, and ability to cause disease. Hypersensitivity to oxidative stress and weak sporulation capacity was only observed in genotype D123E. No competitive advantage was detected for sensitive isolates over the course of five generations when mixed with genotypes H277Y or H134R. The results suggest that in the absence of fungicide pressure, isolates of the H277Y and H134R genotypes may effectively compete with the wildtype population.