Fusarium Species and their Association with Soybean Seed under Humid Tropical Conditions in Puerto Rico

Abstract

Over 90% of all Fusarium isolates from 'Davis' soybeans in Corozal and lsabela, Puerto Rico, were identified as F. semitectum; 3 and 2% were identified as F. oxysporum and F. solani, respectively; and less than 1% each were identified as F. rigidusculum and F. episphaeria var. dimerum. F. semitectum comprised 32.6 and 24.8% of all fungal isolates from seed in Corozal and lsabela, respectively. F. semitectum infected soybean seed germinated 9.4% and 31.1% in seedlots from Corozal and lsabela, respectively. Seed infections of improved Pelican soybeans by F. semitectum were first detected during full green bean stage. Frequency of infection increased rapidly at and after yellow pod stage. In laboratory studies, after pods were incubated 5 days at 95% RH and 27°C, F. semitectum inoculated, wounded and inoculated, and nontreated detached full green pods showed 65, 100, and 9% seed viability losses, respectively. Lima bean pod borer (Etiella zinckenella) injury to soybean pods increased incidence of F. semitectum in intact seed and reduced seed germination and incidence of Phomopsis sp., compared to that found in noninjured pods. Naturally aborted soybean pods had a high incidence of F. semitectum (85%) and low incidence (less than 10%) of Collectotrichum dematium, Phomopsis sp., Botryodiploidia theobromae, and Alternaria tenuissima