Jeremiah K.S. Dung Hermiston Agricultural Research and Extension Center Oregon State University
Species of Pectobacterium and Dickeya Formerly known as soft rot Erwinias P. carotovorum subspecies P. atrosepticum D. dianthicola Anaerobic do not necessarily require oxygen to live and reproduce Pectolytic - produce enzymes which break down pectin molecules
Pectin Various polysaccharides with different functions Located in plant cell walls Binds cells together Cell wall structure
Soft rot bacteria produce pectolytic enzymes which break down pectin Cell walls degrade Plant cells burst Nutrient leakage Tissue death and decay Photo: Dennis Johnson, Washington State University
Large host range, nearly all plant families Storage organs, fruits, succulent and fleshy tissues Asparagus, beans, beet, carrot, corn, onions, pumpkins, watermelon, and POTATO Photo: Lindsey du Toit, Washington State University Photo: Ontario Crop IPM
Excess moisture Anaerobic conditions High relative humidity (RH) Temperature Optimum growth temperatures vary among species Wounding University of Wisconsin-Madison
Tuber soft rot Seed piece decay Blackleg Aerial stem rot Erwinia early dying Lenticel rot
Usually caused by P. carotovorum Other soft rot bacteria Depends on location, environment, other factors Pectobacterium are ubiquitous bacteria found anywhere potatoes are grown Infected or wounded tubers On tuber surfaces, eyes, lenticels Plant debris, soil, water, contaminated machinery, insects
Slight vascular discoloration to complete decay Cream to tan colored often with brown-black margins Photo: Dennis Johnson, Washington State University Soft, cheesy, granular rot Fast progression of symptoms Lenticels, wounds, site of stolon attachment Photo: Jeremiah Dung, Oregon State University
Temperatures above 70 F High moisture and anaerobic conditions Secondary tuber soft rot often follows other diseases Late blight on tubers Fusarium dry rot Pink rot Photo: Phillip Wharton and William Kirk, Michigan State University Photo: Jeremiah Dung, Oregon State University
Ring rot Clostridium soft rot Breaks down starch Phytophthora and Pythium spp. Soft rot caused by Psuedomonas and other bacteria Ring Rot Photo: Jeremiah Dung, Oregon State University Pink Rot Clostridium Soft Rot Compendium of Potato Diseases, 2 nd ed. Leak
Control soft rot bacteria in the field Avoid harvesting when soil temperatures are above 70 F or when soils are excessively wet Reduce wounds during harvest and handling Promote wound healing after harvest Proper ventilation during storage Store tubers below 50 F
Tuber soft rot after planting and before emergence P. carotovorum and others Depends on location, environment, other factors Photo: Dennis Johnson, Washington State University High soil temperatures (>70 F), high moisture after planting Farrar et al. 2009
Seed stock from tissue culture or stem cutting programs carry less bacteria Cut seed when pulp temperatures are 50-55 F Clean/disinfect tools and equipment used for cutting and planting seed Reduce wounds during seed handling and planting Plant suberized seed pieces into well-drained soil (50-55 F) Irrigation prior to emergence increases seed piece decay
Black, soft rot of stems originating from the seed piece Wilting, stunting, poor emergence Typically caused by P. atrosepticum http://www.nwpotatoresearch.com
Bacteria on or in seed pieces Lenticels, eyes, wounds, surface Cool (50-60 F), moist conditions at planting Photo: K. Benlioglu High temperatures (>70 F) after emergence Photo: S. H. De Boer
Plant certified, disease-free tubers into welldrained soil (>50 F) Plant whole seed tubers if possible Suberize cut seed before planting Clean/disinfect tools and equipment used for cutting and planting seed Avoid wounding during seed cutting and planting Avoid irrigation prior to emergence Rogue diseased plants
Caused by various Pectobacterium species Tan to black soft rot of stems originating in the canopy Wilting, chlorosis Wounds Dense canopy, warm temperatures, leaf wetness, previous crop of corn Plant Disease 95:285-291 http://www.nwpotatoresearch.com
Caused by P. carotovorum, P. atrosepticum, and potentially others Vascular infection Wilt, chlorosis, necrosis, premature death Symptoms are similar to Verticillium wilt Wounds Farrar et al. 2009
Plant certified, disease-free seed Reduce wounds on stems Disease is more severe with overhead irrigation Reduce leaf wetness Reduce canopy density avoid excess N Crop rotation Remove infested plant debris
Caused by Pectobacterium species Blemishes Fresh market tubers Thin-skinned, specialty varieties (reds, yellows) Can lead to tuber soft rot Farrar et al. 2009 Photo: Babette Gundersen, Washington State University
LENTICEL ROT Pectobacterium species Infection of lenticels by bacteria Excessive moisture on tubers SWOLLEN LENTICELS Physiological Lenticels enlarge to promote respiration Excessively wet soil, moisture film on tubers Photos: Dennis Johnson, Washington State University
Reduce tuber exposure to flumes or dump tanks Avoid washing with high pressure nozzles Use clean, chlorinated water or water treated with a biocide for washing Dry washed tubers before packaging Provide adequate ventilation during storage and shipping Take extra precautions with specialty cultivars
Use certified, disease-free seed tubers Sanitize and disinfest tuber handling equipment and wash/flume water Avoid injuring tubers Crop rotation Avoid over-irrigation Provide adequate ventilation Dry potatoes before storage or shipping Seed Treatment for Potatoes (maneb+streptomycin @ 1lb/cwt) Firewall (streptomycin sulfate @ 100 ppm)