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Etiology

Moko Disease: Atypical Symptoms Induced by Afluidal Variants of Pseudomonas solanacearum in Banana Plants. A. C. Woods, Associate pathologist, Plant Pathology Department, Vining C. Dunlap Laboratories, United Fruit Co., La Lima, Honduras, Central America; Phytopathology 74:972-976. Accepted for publication 4 February 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-972.

Isolations were made from 1,476 moko-diseased banana plants in Honduras, and the bacteria obtained were classified according to colony morphology. Large fluidal (F) colony types were found in 73% and small fluidal round (SFR) colony types in 10% of the cases. Small afluidal variant (AFV) colony types were associated with either F or SFR colony types in 41% of the cases and occurred alone in 17% of the cases. AFV isolates were morphologically indistinguishable from spontaneous afluidal mutants produced after prolonged still broth culture or storage in water. When inoculated into potted or mature field plants by methods simulating wound infection during routine cultivation, all three colony types incited disease, AFV being the least aggressive. Symptoms typical of moko disease developed in field plants inoculated with F or SFR bacteria. AFV bacteria never caused external symptoms in mature wound-inoculated plants, but suckers arising from the same corms often became stunted and showed discoloration and necrotic areas. Other plants remained symptomless even though invasion by AFV bacteria into corm tissue was evident. Streptomycin-resistant AFV types occurred in 78% of diseased corms from suckers of banana plants inoculated 28 wk previously with a streptomycin-resistant F strain. An average of 18.1% of colony-forming units recovered was of the AFV type. Ten AFV isolates selected from F-inoculated mats were injected into small banana plantlets. All developed wilt and necrosis, although at a reduced rate compared to the F parent. Results suggest that AFV colony types of P. solanacearum have a previously unrecognized potential for causing disease in banana plants.