Chloride requirement for reproduction by Pythium ultimum

Abstract

Chloride (≥ 0.1 mM) was essential for asexual and sexual reproduction, but not mycelial growth, by Pythium ultimum in synthetic culture media. Bromide partially substituted for chloride in support of oogonia formation. The production of gemmae (sporangia or hyphal swellings) increased in proportion to concentrations of KCl in culture media between 0.2 and about 0.5 mM but leveled off between 0.5 and 4 mM. Chloride contents of mycelia after 3 days incubation were proportional to the number of gemmae produced when the fungus was grown in low concentrations of KCl. Under the culture conditions of this study, production of oogonia and gemmae commenced in about 70 and 95 h, respectively, in complete media. When 0.2 mM KCl was added to cultures 95 h or older that were grown in chloride deficient media, oogonium or gemma production was initiated in 20–25 or 10–17 h, respectively. Germination of gemmae, mycelial growth (gain in dry matter), and culture pH were not influenced significantly by the chloride deficiences that prevented sexual and asexual reproduction.Key words: chloride requirement, soilborne plant pathogen, reproduction of fungi, sporangia, hyphal swellings.