Postemergent Herbicides and the Biology of Drechslera Sorokiniana: Effects on Conidial Germination, Vegetative Growth, and Reproduction

Abstract

The synthetic auxinlike postemergent herbicides 2,4-D, 2,4,5-T, 2,4,5-TP, dicamba, and MCPP were examined for their influence on conidial germination, germ-tube growth, primary branching of germ tubes, and conidial production of Drechslera sorokiniana at molar concentrations of 10-1 to 10-3. All herbicides of the 10-3 M concentration prohibited conidial germination and caused visible plasmolysis of conidium cells. Germination of conidia was not affected by any herbicides at concentrations of 10-~1 to 10-4 M. Germ-tube growth and primary branching of germ tubes were stimulated by most herbicides at concentrations of 10-12 to 10-4 M; some nonsignificant inhibition of these structures occurred in response to 2,4,5-TP and MCPP. Mycelial growth was stimulated by most herbicides at concentrations of 10-12 to 10-4 M; significant increases within this concentration range, however, differed with specific herbicides. Conidial production was inhibited by 2,4,5-T and MCPP at all concentrations; 2,4,5-TP and dicamba caused significant increases in conidial production at lower concentrations and a significant decrease at higher concentrations. Only 2,4-D increased conidial production at higher concentrations. The results of the investigation indicate that germ-tube growth is most dramatically stimulated by the herbicides examined and that vegetative growth