Effect of Sporulating Temperature on the Limit Temperature of Indirect Germination of the Sporangia of Phytophthora infestans

Abstract

The ability of indirect germination of the spores (sporangia) of Phytophthora infestans at different water temperatures was investigated. Spores appeared to have their own limit temperature of indirect germination (LT): only when water temperature was below the LT, spores could germinate. Variation of LT was investigated by using spore suspensions prepared from the infected potato tuber disks cultured for different periods (16, 24 and 48hr) at different air temperatures (12-26°C). The suspensions were incubated for 24hr at different water temperatures (14-25°C). Irrespective of the sporulating air temperatures, in all the suspensions the proportions of germination at below 16°C were equally high. But at different water temperatures between 16 and 20°C the proportions turned to rapid decrease: the decrease from 90 to 10% occurred with increase of only about 3°C. The water temperature limiting germination to 50% (LT₅₀) was fairly affected by sporulating air temperature. When produced at the lower air temperatures of 12 and 15°C, the spores had lower LT₅₀s (17.0-18.6°C), whereas at the higher air temperatures of 24 and 26°C, the spores had higher LT₅₀s (20.5-22.5°C). The LT₅₀ was also somewhat affected by the time of culture period. The spores from the shortest period of cultures usually had somewhat lower LT₅₀s than those from the older ones. Therefore, the level of LT of spores appeared to be determined mainly by sporulating air temperature and secondary by their ages.