When mature 30-d-old oospores of Phytopthora cactorum were tested for germination immediately after harvesting from culture, 30% germinated in sterile glass distilled water and 90% in soil extract; however, after oospores had been stored at 2–4 °C in sterile distilled water for 2 or more weeks, germination was less than 1% in water, but increased to 80% in filter-sterilized soil extract, oospores exudate, mycelial exudate, and alfalfa root exudate. When similarily-treated oospores were incubated in solutions of amino acids, sugars, organic acids, various salts, urea, and adenine, oospores germinated (35–75%) only in the amino acid solutions. The maximum and minimum concentrations of alanine and glycine for stimulation of oospore germination were 10 and 0·1 mm, respectively. About 30–80% activation (erosion of the inner oospore wall without germination) occurred in solutions of sugars, nitrate salts, urea and in distilled water, but germination did not occur. When either sucrose or a mineral salt solution was added to alanine at 1 mm, the percent germination of oospores was higher than with alanine alone. Activated oospores in sucrose (10 mm) germinated only when sucrose was replaced by alanine (10 mm). The germination of oospores in undiluted and diluted soil extract (1:10) was 75% but in undiluted soil extract from combusted soil, germination was reduced to 56·6%, and in dilutions of 1:10 and 1:100 none of the oospores in combusted soil extract germinated. © 1993, British Mycological Society. All rights reserved.
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