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Induction of Rhizopus oryzae Germination Under Starvation Using Host Metabolites Increases Spore Susceptibility to Heat Stress

Turgeman Tidhar, Kakongi Nathan, Schneider Avishai, Vinokur Yakov, Teper-Bamnolker Paula, Carmeli Shmuel, Levy Maggie, Skory Christopher D., Lichter Amnon, Eshel Dani
Phytopathology 2014 v.104 no.3 pp. 240-247
DNA fragmentation, Rhizopus oryzae, apoptosis, deformation, dietary nutrient sources, disease control, fluorescent dyes, germ tube, heat stress, humans, metabolites, pathogens, shrinkage, spore germination, spores, starvation, sweet potatoes, vacuoles
Sweetpotato 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 sweetpotato active fractions (SPAFs) that induce spore germination and used them at a low dose to enhance spore weakening caused by starvation. Germination in SPAF at 1 mg/ml 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 assays. Spores incubated with SPAF at 1 mg/ml 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.