Comparison of isolates of Colletotrichum orbiculare from Argentina and Australia as potential bioherbicides for Xanthium spinosum in Australia

In Australia, the fungus Colletotrichum orbiculare (Berk. and Mont.) v. Arx is a naturally occurring pathogen of the weed Xanthium spinosum L., Bathur st burr, a native of Argentina, and, for many years, a serious weed of east ern Australia. Attempts to develop the fungus as a bioherbicide have been h ampered by its requirement for an extended period of dew or free water for satisfactory control of X. spinosum. Collections of C. orbiculare from a ra nge of environments in Argentina were made in the hope of finding an isolat e with shorter dew period requirements. None of several isolates of C. orbi culare from Argentina tested were superior to an Australian isolate in cont rolling X. spinosum over a range of dew periods: 0, 4, 8, 24 h. In addition , none of the Argentinian isolates were superior to the Australian isolate in terms of vegetative growth rate and conidia production in vitro. Develop ment of a formulation of the Australian isolate of C. orbiculare which has a reduced dew requirement remains as the most likely means of utilizing thi s fungus as a biocontrol agent for X. spinosum. (C) 1999 Elsevier Science B .V. All rights reserved.