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United States Department of Agriculture

Agricultural Research Service

Research Project: NOVEL TECHNOLOGIES FOR PRODUCING RENEWABLE CHEMICALS AND POLYMERS FROM CARBOHYDRATES DERIVED FROM AGRICULTURAL FEEDSTOCKS

Location: Renewable Product Technology Research Unit

Title: Induction of Rhizopus oryzae germination under starvation using host metabolites increases spore susceptibility to heat stress

Authors
item Turgeman, Tidhar -
item Kakongi, Nathan -
item Schneider, Avishai -
item Vinokur, Yakov -
item Teper-Bamnolker, Paula -
item Carmeli, Shmuel -
item Levy, Maggie -
item Skory, Christopher
item Lichter, Amnon -
item Eshel, Dani -

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 17, 2013
Publication Date: December 11, 2013
Citation: Turgeman, T., Kakongi, N., Schneider, A., Vinokur, Y., Teper-Bamnolker, P., Carmeli, S., Levy, M., Skory, C.D., Lichter, A., Eshel, D. 2014. Induction of Rhizopus oryzae germination under starvation using host metabolites increases spore susceptibility to heat stress. Phytopathology. 104(3):240-247.

Interpretive Summary: The fungus Rhizopus is causative agent of soft rot, which is a common worldwide disease affecting the post harvest storage of the sweet potato. Infections typically result in a rapid degradation of the root, so methods to inhibit Rhizopus are critical for minimizing major loss of the product. In this work, we isolated a compound from sweet potato that triggers a starvation-like condition in Rhizopus that renders the fungus more susceptible to stress. The fungus showed signs of cellular death and it was significantly more vulnerable to heat treatment after exposure to the active compound. This work furthers our understanding of the fungus Rhizopus and may provide a new strategy for pathogen control, resulting in considerable savings for the sweet potato industry.

Technical Abstract: Sweet potato is a nutritional source worldwide. Soft rot caused by Rhizopus spp. is a major limiting factor in the storage of produce, rendering it potentially unsafe for human consumption. In this study, Rhizopus oryzae was used to develop a concept of postharvest disease control by weakening the pathogen through induction of spore germination under starvation conditions. We isolated the active compounds in sweet potato (SPAC) that induce spore germination and used them at a low dose to enhance spore weakening caused by starvation. Germination in 1 mg/ml SPAC weakened the pathogen spores by delaying their ability to form colonies on rich media and by increasing their sensitivity to heat stress. The weakening effect was also supported by reduced metabolic activity as detected by Alarmar Blue fluorescent dye assay. Spores incubated with 1 mg/ml SPAC showed DNA fragmentation in some of their nuclei, as observed by TUNEL assay. In addition, these spores exhibited changes in ultrastructural morphology, i.e. shrinkage of germ tubes, nucleus deformation and vacuole formation, which are hallmarks of programmed cell death. We suggest that induction of spore germination under starvation conditions increases their susceptibility to stress and therefore might be considered a new strategy for pathogen control.

Last Modified: 9/20/2014
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