Acrocalymma medicaginis and Phomopsis sp. as Causal Agents of Crown Rot of Lucerne in Australia

Abstract

AbstractFungi associated with crown rotting were isolated from 3 year‐old lucerne plants growing in sandy and loam soils in an irrigated stand, declining in productivity, at Langhorne Creek, South Australia. The method of isolation markedly affected the range of species recovered. Fusarium spp. and Phomopsis sp. were isolated from washed and surface sterilized crowns, whereas a larger range of fungi, especially Acrocalymma medicaginis, was isolated from unwashed crowns. A. medicaginis was most frequently isolated from rotted tissue flecked with red, while a species of Phomopsis was the dominant fungus in whitish tissue containing zone lines, especially in crown branches. A. medicaginis and Phomopsis sp. caused crown rotting of mature, wounded lucerne plants at temperatures equivalent to summer conditions at Langhorne Creek. There was no evidence that Fusarium oxysporum or F. solani, two of the most frequently isolated species, were pathogens of mature lucerne plants.