Incidence of pectolytic erwinias associated with blackleg of potato in Rio Grande do Sul

Abstract

Erwinia carotovora subsp. atroseptica (Eca), E. carotovora subsp. carotovora (Ecc) and E. chrysanthemi (Ech) may cause potato (Solanum tuberosum) blackleg. To determine the occurrence of these pathogens in the conditions found in the State of Rio Grande do Sul (RS), potato plants showing blackleg symptoms were harvested from 22 fields in nine counties in Serra do Nordeste, Planalto, Depressão Central, and Grandes Lagoas, from September to December of 1999 (Spring-Summer season). Green pepper (Capsicum annuum) fruits were used as a host to enrich for pectolytic erwinia from potato stems with blackleg symptoms. Bacteria were subsequently isolated on non-selective medium. Isolates that were Gram-negative, facultatively anaerobic, and pitted crystal-violet-pectate medium were tested for biochemical traits to identify the species and subspecies. Four hundred strains were identified as either Eca, Ecc or Ech. Although the three erwinias were found in RS potato fields, only three strains of Ech were found in one field. Frequencies of Eca and Ecc were 55 and 42%, respectively. Eight strains could not be assigned based on the biochemical characterization.

Cardinal temperature differences, determined in vitro, between closely related species and subspecies of pectinolytic bacteria responsible for blackleg and soft rot on potatoes

“…This is contradictory to the results of Pérombelon and Hyman (1986) which indicated a lack of growth of Pcc at 37°C, but confirms results of Oliveira et al (2003) who found Pcc to grow at 37°C. The differences in optimal temperatures for growth can have important consequences in industry as a slight decrease in temperature could result in Pcb becoming dominant in the field, and this subspecies has been reported to be more virulent than other Pectobacterium spp.…”

“…This unique characteristic could be used to distinguish Pba from other pathogenic species causing soft rot and blackleg in potato, as proposed by De Boer and Kelman (2001). However, up to 10% of Pba isolated are atypical and able to grow at temperatures above 37°C (Pérombelon and Hyman 1986;Oliveira et al 2003). Using temperature to characterise species might therefore result in incorrect characterisation in cases where atypical isolates are encountered.…”

“…Pectobacterium atrosepticum grows optimally in cool to temperate (15°C to 24°C) and wet environmental conditions, although some isolates have been shown to survive at temperatures of up to 37°C Pérombelon 1992;Pérombelon and Salmond 1995;Oliveira et al 2003;Duarte et al 2004;Smadja et al 2004;Elphinstone and Toth 2007). Pectobacterium carotovorum subsp.…”

Erwinia chrysanthemi: pectolytic bacterium causing soft rot outbreaks of arracacha in Brazil

“…are very harmful and occur in a large number of agricultural crops in Brazil, there are few papers published on the pathogen recently. In a survey on potato plants showing blackleg symptoms in 22 fields of nine counties in Rio Grande do Sul State, 55% of the strains were identified as Eca, 44% as Ecc and only 1% as Ech (Oliveira et al, 2003). Arracacha soft rot continues to be a very important postharvest disease during summertime in Brazil, causing severe losses.…”

“…The predominance of Ech (89.8%) causing soft rot in arracacha roots in Brazil is a novel finding, since previous papers reporting the disease considered Ecc as the predominant one (Romeiro et al, 1988;Lopes & Quezado-Soares, 1997), although based on the identification of few isolates. Lately, Oliveira et al (2003) described Eca (55%) and Ecc (44%) as the predominant subspecies in potato fields in Southern Brazil, which was unexpected, and more recently, Duarte et al (2004) reported a new, atypical potato blackleg strain called E. carotovora subsp. brasiliensis.…”