Etiology of potato soft rot and blackleg diseases complex in Egypt

Abstract

Recent observations of increasing incidences of potato plants showing blackleg symptoms have caused serious concern for potato growers and traders in Egypt. Potato plants showing blackleg and soft rot symptoms were sampled from main potato-growing areas in Egypt during three successive seasons. Dickeya spp., Pectobacterium carotovorum and Pectobacterium atrosepticum were successfully isolated and identified from symptomatic potato plants (tubers and stems). The identity of bacterial isolates was reviled by identification methods based on different biological principles: cultural, biochemical and molecular methods. Specific primers targeting different genomic loci were selected for molecular identification, utilizing either conventional or real-time PCR. Multiple species were isolated from some infected samples revealing complex infection, which confirm the complexity and interaction of soft rot and blackleg diseases. Given that no previous reports on Dickeya diseases in Egypt were confirmed since the recent revision of its taxonomy, the result of PCR with Dickeya spp. was furtherly confirmed using DNA sequencing assay. BLASTn analyses of 16S rDNA sequences showed similarity to several species of Dickeya, with 99% nucleotide similarity to strains of, D. chrysanthemi, D. dianthicola and D. solani, respectively. Furthermore, the most commonly identified bacterial pathogen in the tested samples was P. carotovorum followed by P. atrosepticum and Dickeya spp., while P. brasiliense was never detected in any of the collected samples confirmed by real-time PCR assay. The results of such field survey suggested to help the decision makers in Egypt to establish an action plan to face the increasing risk of potato diseases caused by Dickeya spp. for the benefit of Egyptian domestic production.