Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/29/2001
Publication Date: 11/20/2001
Citation: SCHROEDER, B., LUPIEN, S.L., DUGAN, F.M. FIRST REPORT OF PINK SEED OF PEA CAUSED BY ERWINIA RHAPONTICI IN THE UNITED STATES. PLANT DISEASE. 2001. v. 86. p. 188. Interpretive Summary: Pink seed is a disease normally associated with wheat, but has in Canada also been reported from field pea. The disease is considered of minor importance, although severely affected lots can be subject to dockage. However, the disease symptoms mimic the appearance of pink-colored pesticides frequently applied to peas destined for planting in the field. Lots with suspected pesticide contamination may not be used for human or animal consumption. It is therefore critical to be aware of the disease, and to be able to distinguish its symptoms from the pink-colored coatings originating with pesticidal seed treatment. This short article is intended for Disease Notes, a short article section of the journal Plant Disease. By its appearance, readers will be alerted that the disease has appeared in lots of field peas shipped in the United States, and how to distinguish the disease symptoms from pesticide-treated peas.
Technical Abstract: In March 2001, discolored seed of field pea (Pisum sativum L.) originating from north-eastern Montana was sent for analysis to USDA-ARS by the USDA Federal Grain Inspection Service. Symptoms consisted of pale, pinkish- brown to bright pink discoloration throughout the seed coat. Unlike the pink coloration resulting from application of pink-color, pesticidal seed treatments, the coloration was permanent and could not be removed by extended washing. Discolored seeds were disinfested in 0.5 percent NaOCl prior to placement onto malt extract agar amended with antibiotics, or onto nutrient broth yeast extract agar (NBY) and incubation at ambient lab conditions. Pale pink bacterial colonies were recovered from NBY, streaked for selection of single colonies, stored at 4 degrees C and revived for growth in shaking NBY broth. Three pea plants and one control plant were grown in the greenhouse until pods were sufficiently developed to be syringe-inoculated with bacterial culture. The experiment was repeated. Pods on inoculated plants but not the controls exhibited pale, pinkish areas and later produced seeds discolored in shades of pink matching those from the original sample. Two isolates from the original sample and two recovered from the experimental inoculations were tested for anaerobic and aerobic growth using API 50 CHE and API 20 NE tests (bio Merieux Vitek, Inc., Hazlewood Missouri). Known strains of Erwinia rhapontici were identically analyzed for comparison. All four strains from pea were Gram- negative, facultatively anaerobic, motile rod-shaped bacteria that produced a diffusible pink pigment on NBY. Tests indicated that these strains were E. rhapontici because of agreement of results with the published data and congruence with known tester strains. Previously reported in Alberta, Can.