The use of plant phatogenic Helminthosporium euphorbiae for the control of Euphorbia heterophylla

Abstract

The genus Helminthosporium is known as an important pathogen of cereal crops such as barley, corn, rice and wheat. Several species of this genus are reported as toxin producers causing several types of leaf lesions, spots, discoloration or root and stem rots. The species H. euphorbiae (sin. Bipolaris euphorbiae) has been studied as a biological control agent for wild groundnut, Euphorbia heterophylla, a common weed that infests soybean fields and is responsible for considerable yeld losses and for the continued use of herbicides, resulting in increased production costs. The weed competes with the soybean for water, light and nutrients, and can also reduce grain quality by conferring moisture from the green stem that is mixed with the grain at harvest. H. euphorbiae causes total defoliation of the weed when apllied either as spore suspension, similar to herbicide application or as a culture filtrate of the liquid culture medium where it is grown. This effect is a result of the ability of the fungus to produce a weed specific toxin which is excreted extracellularly causing foliar symptoms. The objective of this work was to review the current knowledge on H. euphorbiae as a biological agent for weed control and the mode of action of other Helminthosporium species that cause important crop diseases.