Rhizosphere Effect of Herbicide-Stressed Sicklepod (Cassia obtusifolia) on Chlamydospores of Fusarium oxysporum f. sp. vasinfectum. Stephen L. Brown, Pesticide Education Specialist, Alabama Cooperative Extension Service. E. A. Curl, Professor, Department of Plant Pathology, Alabama Agricultural Experiment Station, Auburn University 36849. Plant Dis. 71:919-922. Accepted for publication 29 January 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0919.

Equal concentrations of sterile seed + root exudates from eight weed-plant species promoted higher levels of chlamydospore germination of Fusarium oxysporum f. sp. vasinfectum and induced more rapid germ-tube extension than occurred in sterile, demineralized water. Germination ranged from 91% in spurred anoda (Anoda cristata) exudate to 49% in goosegrass (Eleusine indica) exudate and 24% in water. Germination in sicklepod (Cassia obtusifolia) exudate was 83%. Linuron-treated sicklepod seedlings cultured in a system of water and glass beads liberated 19.8% more exudate than untreated plants, but chlamydospore germination in exudates from these two sources did not differ significantly, nor was germination different in rhizosphere soil collected from treated and untreated plants growing in a sterile system. Spore germination, however, was significantly suppressed in rhizosphere soil from roots of herbicide-treated sicklepod growing in natural (nonsterilized) soil. Populations of Fusarium spp. and the general fungal flora of the rhizosphere also were reduced compared with populations in the rhizosphere of untreated plants. These results suggest a foliar-herbicide-induced influence on soil fungistasis in the rhizosphere of declining target plants after treatment.

Keyword(s): microbial populations.