Co-Authors:
Buskila, Y., Department of Postharvest Science, ARO, Volcani Center, Bet Dagan, Israel
Tsror, L., Department of Postharvest Science, ARO, Volcani Center, Bet Dagan, Israel
Sharon, M., Department of Plant Science, Faculty of Life Science, Tel-Aviv University, Israel
Teper-Bamnolker, P., Department of Postharvest Science, ARO, Volcani Center, Bet Dagan, Israel
Holczer-Erlich, O., Department of Plant Pathology and Weed Research, ARO, Gilat Research Center, Israel
Warshavsky, S., Department of RandD, Hevel Maon Enterprises, Negev, Israel
Ginzberg, I., Department of Plant Science, ARO, Volcani Center, Bet Dagan, Israel
Burdman, S., Department of Plant Pathology and Microbiology, Robert H. Smith Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, Israel
Eshel, D., Department of Postharvest Science, ARO, Volcani Center, Bet Dagan, Israel
Abstract:
Israeli farmers export 250,000 tons of potato tubers annually, ̃40,000 tons of which are harvested early, before skin set. In recent years, there has been an increase in the occurrence of dark skin spots on earlyharvested potato tubers ('Nicola') packed in large bags containing peat to retain moisture. The irregular necrotic spots form during storage and overseas transport. Characterization of the conditions required for symptom development indicated that bag temperature after packing is 11 to 13°C and it reaches the target temperature (8°C) only 25 days postharvest. This slow decrease in temperature may promote the establishment of pathogen infection. Isolates from typical lesions were identified as Rhizoctonia spp., and Koch's postulates were completed with 25 isolates by artificial inoculation performed at 13 to 14°C. Phylogenetic analysis, using the internal transcribed spacer sequences (ITS1 and ITS2) of rDNA genes, assigned three isolates to anastomosis group 3 of Rhizoctonia solani. Inoculation of wounded tubers with mycelium of these R. solani isolates resulted in an oversuberization response in the infected area. With isolate Rh17 of R. solani, expression of the suberin biosynthesis-related genes StKCS6 and CYP86A33 increased 6.8- and 3.4-fold, respectively, 24 h postinoculation, followed by a 2.9-fold increase in POP-A, a gene associated with wound-induced suberization, expression 48 h postinoculation, compared with the noninoculated tubers. We suggest that postharvest dark spot disease is an oversuberization response to R. solani of AG-3 infection that occurs prior to tuber skin set. © 2011 The American Phytopathological Society.
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