Virulence of Phakopsora meibomiae in wild and cultivated legumes in Puerto Rico

Abstract

Soybean rust is caused by two Phakopsora species: Phakopsora meibomiae (Arthur) Arthur and P. pachyrhizi H. Sydow and Sydow. Phakopsora meibomiaeis found only in limited areas in the Western hemisphere, and it is not known to cause severe losses. Phakopsora meibomiae was reported in Puerto Rico in 1913 infecting Lablab purpureus and in 1976 an outbreak produced severe yield losses in soybeans, common beans, and lima beans in Adjuntas. Phakopsora meibomiae infects approximately 60 species of legumes and may represent a potential threat to soybean production in Puerto Rico. This study determined the virulence of one isolate of P. meibomiae in fifteen legumes. Eleven of the fifteen species inoculated developed rust symptoms, and the identity of the rust fungus was confirmed by Polymerase Chain Reaction (PCR). Symptoms were observed first on Phaseolus vulgaris, P. lunatus, and V. unguiculata. Phaseolus vulgaris and P. lunatus had the shortest incubation and latent periods. Phaseolus vulgaris also produced the highest number of uredinia per individual lesion. Crotalaria retusa had the longest incubation period, and Rhynchosia reticulata had the longest latent period. Phakopsora pachyrhizi was not observed infecting legumes in Puerto Rico in areas where it had previously been reported.