Potato blackleg: Epidemiology, host-pathogen interaction and control

Abstract

Blackleg is caused by Erwinia carotovora subsp, atroseptica (Eca) and E. chrysanthemi (Echr) in cool and hot climates respectively. The bacteria are opportunistic pathogens and rely on their strong pectolytic character to infect plants when conditions favor their multiplication. Blackleg is a seedborne disease and the bacteria can survive in a quiescent form in lenticels and wounds during storage. The contaminated mother tuber and not the blackleg plant is the main source of progeny tuber contamination. Other sources of the pathogen are airborne (insects and aerosols) erwinias deposited on leaves and from there to the soil and progeny tubers, and erwinias in rotting tubers smeared into wounds incurred during mechanical crop handling.Most seed tubers are contaminated but blackleg incidence is related to seed contamination level modulated by soil water status. Competitiveness of the erwinias in the rotting mother tuber is affected by temperature, Eca is favored at <25 ~ and Echr at higher temperatures. The ubiquitous E. carotovora subsp, carotovora apparently fails to compete successfully with the other erwinias and saprophytic pectolytic bacteria in mother tubers and therefore does not cause blackleg.Disease control measures are based on avoiding tuber contamination by cultural means (early harvesting), reducing tuber contamination level (dry storage and hot water treatment) and planting 'clean' seed identified by quantifying tuber contamination rather than by visual crop inspection. Finally, recently identified highly resistant, even under anaerobic conditions, wild Solanum spp. could be used to breed for resistant cultivars by conventional methods or by genetic engineering.

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

“…Temperature plays an important role in pathogenicity differentiation of soft rot and blackleg pathogens (Pérombelon and Kelman 1980;Pérombelon et al 1987;Pérombelon 1992 (Pérombelon and Kelman 1980;Elphinstone 1987;Pérombelon et al 1987;Pérombelon 1992;Tsror et al 2009Tsror et al , 2013. Each of these blackleg and soft rot bacterial species, however, prefer specific temperatures at which they cause disease.…”

“…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.…”

“…Pectobacterium carotovorum subsp. carotovorum prefers temperate and tropical environments, with optimal temperatures between 25°C and 28°C (Pérombelon 1992;Pérombelon and Salmond 1995;Smadja et al 2004). Pectobacterium carotovorum subsp.…”

Factors affecting bacterial soft rot ofZantedeschiatubers

“…High soil moisture levels, caused by high rainfall, excessive irrigation, and heavy and poorly drained soils, are conducive to disease caused by softrotting bacteria (Civeolo 1982;Perombelon 1992). Water covering tuber surfaces can cause anaerobic conditions inside potato tubers; subsequently oxygen becomes depleted by tissue respiration and the host defences against infection become impaired (Burton & Wigginton 1970;Bourne et al 1981;Klement et al 1990;Gudmestad & Secor 1993).…”

Effects of cessation of irrigation and time of lifting of tubers on bacterial soft rot of calla(Zantedeschiaspp.) tubers

“…The incidence of bacterial soft rots in potato (Solanum tuberosum) tubers that are harvested early are often lower than in tubers that are left in the soil for a longer period. Early-harvested potato tubers are not exposed to high numbers of bacteria that build up on rotting leaves and are washed into the soil, nor are they exposed to extended periods of wet soil which favours tuber infection by E. carotovora (Perombelon 1992). The effects of waterlogged soils on infection of potatoes (Gudmestad & Secor 1993), other root vegetables (Walker 1952), and ornamental bulbs (Moore 1979) by E. carotovora are well documented.…”