EFFECT OF TEMPERATURE ON CONIDIAL GERMINATION AND SYSTEMIC INFECTION OF MAIZE BY PERONOSCLEROSPORA SPECIES

Peronosclerospora maydis from Java, Indonesia, and the maize strain of P. sorghi from Thailand, both apparently infective only to maize, and P. philippinensis from the Philippines had very broad optimum temperature ranges for germination (at least 10-30 C) and germ tube growth (18-30 C); they produced large numbers of conidia from 18 to 23 C (the optimum temperature for sporulation) in presence of dew for 5-6 h. P. maydis usually, and the maize strain of P. sorghi always, caused high levels of systemic infection from 8 to 36 C. P. philippinensis consistently had less systemic infection with dew periods at the lower temperatures of 10-16 C. This lower systemic infection for P. philippinensis is similar to that previously reported for P. sacchari, an organism we believe to be conspecific with P. philippinensis. The sorghum strain of P. sorghi (true P. sorghi), common in many countries on sorghum and/or maize but not found in Thailand or Java, was characterized by a relatively narrow optimum temperature range for germination (about 12-20 C), relatively short germ tubes at the optimum temperature for germ tube growth, and low amounts of systemic infection at temperatures less than about 15 C and greater than 30 C.