Low Concentrations of the Isoflavone Genistein Influence in vitro Asexual Reproduction and Growth ofPhytophthora sojae

Abstract

Isolates of Phytophthora sojae were evaluated for their sensitivity to a series of low concentrations of genistein (0.01, 0.1, 1, 3, and 10 μg/ml) during various stages of growth and asexual reproduction. Genistein was applied during mycelial growth, formation of zoosporangia, release of zoospores, and zoospore germination. At 10 μg/ml, genistein inhibited radial growth of all isolates in solid culture. Changes in fungal morphology, such as increased branching and swelling of hyphae, were observed at all concentrations of genistein tested. Growth of mycelium in broth containing 10 μg of genistein per ml decreased colonies resulting from subsequently formed and germinated zoospores, even when genistein was removed during zoosporangia formation. Genistein also decreased zoosporangia production and release of zoospores. The strongest inhibition of P. sojae reproduction was obtained when genistein was applied during zoosporangia formation ; this occurred at concentrations as low as 0.01 to 1 μg/ml. Genistein in the medium containing zoospores caused a general reduction in asexual reproduction across isolates, with 10 μg/ml causing the most dramatic reduction. There was strong evidence of intraspecific variation in the responses of the isolates of P sojae in all processes tested.