Date of Award

Winter 12-15-2016

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Advisor

Jianjun Hao

Second Committee Member

Gregory Porter

Third Committee Member

Seanna L. Annis

Abstract

Pink rot of potato (Solanum tuberosum) is a widespread soilborne disease that causes significant losses in the field and storage. It is caused by Phytophthora erythroseptica (Pethybr.), an oomycete pathogen that produces sexual spores that can survive in soil for years. The management of pink rot mainly relies on chemical control. However, the most effective chemical in pink rot control, mefenoxam, is losing its efficacy owing to the development of mefenoxam resistance in P. erythroseptica. To evaluate alternative fungicides (including chemical and biological fungicides) to mefenoxam in pink rot control, two greenhouse experiments and three field trials were conducted. Crop rotation experiments were performed in the field to investigate the rotation effects of alfalfa, barley-ryegrass, canola, red clover, onion, pumpkin, sweet corn and oats on pink rot of potato. Thirty-four wild-type isolates of P. erythroseptica were collected for fungicide sensitivity assay and fungicide-resistant P. erythroseptica selection, to predict the resistance risk of fluopicolide, an alternative chemical to mefenoxam. Field trials showed that biologicals including Bacillus subtilis (Serenade Soil, Taegro), Bacillus amyloliquifaciens (Double Nickel, MBI-110), and extract of Reynoutria sachalinensis (Regalia) did not significantly reduce pink rot severity in the harvested potato tubers. The sole application of fluopicolide, some combinations of chemical fungicides (mefenoxam and oxathiapiprolin) and some combinations of chemical and biological fungicides (oxathiapiprolin/fluopicolide and Bacillus sp.) significantly reduced pink rot severity in the presence of mefenoxam-resistant P. erythroseptica population. In crop rotation trials, alfalfa, canola and pumpkin significantly increased potato tuber yield. However, the rotation crops had no significant effect on pink rot of potato. The results of the fungicide resistance study suggested a medium risk of P. erythroseptica developing intermediate resistance to fluopicolide, and that there was a trade-off between fluopicolide resistance and biological fitness in P. erythroseptica.

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