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

item TURGEMAN, TIDHAR - Volcani Center (ARO)
item KAKONGI, NATHAN - Volcani Center (ARO)
item SCHNEIDER, AVISHAI - Volcani Center (ARO)
item VINOKUR, YAKOV - Volcani Center (ARO)
item TEPER-BAMNOLKER, PAULA - Volcani Center (ARO)
item CARMELI, SHMUEL - Tel Aviv University
item LEVY, MAGGIE - Hebrew University Of Jerusalem
item Skory, Christopher - Chris
item LICHTER, AMNON - Volcani Center (ARO)
item ESHEL, DANI - Volcani Center (ARO)

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2013
Publication Date: 12/11/2013
Publication URL:
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.