Fungi on Commelina benghalensis from Brazil, with notes on potential for weed biological control

Abstract

Commelina benghalensis (tropical spiderwort - TS) is an invasive herbaceous plant, native to South and Southeast Asia and one of the worst agricultural weeds in the tropics. Its management is notoriously difficult because of its ability to regenerate from small fragments and its tolerance to glyphosate applications. There are no published records of biocontrol attempts against TS involving either microbial or arthropod natural enemies. Prior to investigating classical biocontrol agents, surveys have been conducted in Brazil and, more recently, concentrated in Viçosa (state of Minas Gerais) to determine whether fungal pathogens of TS are already present. Five different fungal pathogens were collected. These fungi were identified as causing the following diseases: Athelia rolfsii – crown rot, Cercospora cf. sigesbeckiae – leaf spots, Corynespora cassiicola – leaf spots, Neopyricularia obtusa sp. nov. – leaf spots and Rhizoctonia solani – blight. One of the fungi found on TS represents a new taxon, and the others represent either a new host association, a new geographic record or both, except for Corynespora cassiicola, which has already been recorded as able to attack TS (ex-tomato isolates, under controlled conditions) in Brazil. The mycobiota identified in Brazil is limited and lacks many of the TS-specific fungal pathogens recorded in Africa and Asia, namely: Kordyana celebensis, Kordyana indica, Phakopsora tecta, Puccinia commelinae, Uredo ochracea, Bauerago combensis and Bauerago commelinae. It is conjectured here, that such exotic fungi, may offer a valuable resource for management of one of the worst agricultural weeds in Brazil and in the tropical world, and require investigation as biological control agents for introduction in Brazil.