Dickeya solani, Pectobacterium atrosepticum and Pseudomonas asplenii: causal agents of bacterial soft rot in cyclamen plants (Cyclamen persicum Mill.) in Colombia

Abstract

Cyclamen (Cyclamen persicum Mill.) is an ornamental plant affected by various phytosanitary issues including bacterial soft rots, which cause crop losses of 20% worldwide. In Colombia, however, the symptoms of bacterial soft rots are not well described and the causal agents are unknown. This study aimed to characterize the bacterial soft rot disease according to its symptoms, and identify its causal agents at the species level. For this purpose, we visited nurseries in the municipality of San Antonio del Tequendama, Colombia, and selected diseased plants to describe symptoms, and to isolate and characterize pathogens using morphological, biochemical, and molecular methods. Soft rotting activity in potato tubers and pathogenicity in cyclamen plants also was evaluated. Six symptoms were found to be associated with the disease, namely: wilt, soft corm, bacterial exudates on corms, root rot, soft rot and necrotic soft rot on petioles and peduncles. Of 47 isolates, seven were pathogenic: one from the soft corms; two from petioles with soft rot; two from petioles with necrotic soft rot; and two from root rot. A multiple correspondence analysis clustered isolates in the genera Pseudomonas, Dickeya and Pectobacterium based on the morphological, biochemical, and pathogenic characteristics. A multi-locus analysis (MLSA) based on sequencing of the 16S rDNA region and housekeeping genes (gapA, icdA, mdh, pgi, rpoB and rpoD) confirmed the bacterial species Pseudomonas asplenii, Dickeya solani and Pectobacterium atrosepticum as the causal agents of cyclamen bacterial soft rot in Colombia.