1994 Volume 60 Issue 1 Pages 53-59
The rapidity of indirect germination of the sporangia of Phytophthora infestans was investigated. Sporangial suspensions were prepared from the infected potato tuber slices or disks cultured for various periods at different temperatures. When the suspensions were incubated at 14°C, optimum for indirect germination, sporangia from older cultures could germinate more quickly than those from younger cultures. Sporangia immediately after production could germinate only slowly, while almost all the sporangia aged by preincubation for 6hr or more at 22°C could germinate quickly within 1hr when postincubated at 14°C. Therefore, it was considered that sporangial maturation by aging was essential to acquire the ability of indirect germination, and that matured sporangia could germinate quickly within about 1hr at 14°C. Time required for sporangial maturation was remarkably affected by the air temperature during sporangial production and also by the incubation temperature after preparation of sporangial suspension. The shortest maturation time, about 6hr, was found between 18 and 22°C. Temperatures below 15°C remarkably slowed maturation, and temperatures of 26°C and above inhibited it. Matured sporangia quickly lost the ability of quick germination when the suspensions were incubated at 26°C or above.