Influence of temperature on in vitro zoosporogenesis of Pythium insidiosum.

This study verified the influence of different temperatures on P. insidiosum in vitro zoosporogenesis. P. insidiosum isolates (n = 26) were submitted to zoosporogenesis and incubated at 5 degrees C, 15 degrees C, 20 degrees C and 37 degrees C (1st stage). Grass fragments were evaluated under optical microscopy at 4, 8, and 24 hours of incubation. Afterward, all isolates were incubated at 37 degrees C and assessed at the same periods of time (2nd stage). The development of hyphae, presence of vesicles, zoosporangia and zoospores were checked. Only the presence of short hyphae was observed at 5 degrees C. At 15 degrees C, the hyphae were either under development or elongated and two isolates produced zoospores. When the isolates were submitted to 20 degrees C for 4 hours, the presence of long and mycelial hyphae, vesicles, zoosporangia and zoospores was observed, which also happened at the other periods evaluated. In the second stage, the isolates which were initially at 5 degrees C and 15 degrees C evidenced long developing hyphae with the presence of vesicles, zoosporangia, and zoospores within 4 hours of incubation, and these characteristics were kept at the other evaluated periods. The isolates kept at 37 degrees C showed evident zoosporogenesis in the first 4 hours of evaluation. It was concluded that temperatures of 20 degrees C and 37 degrees C support P. insidiosum zoosporogenesis process. On the other hand, 5 degrees C and 15 degrees C temperatures do not kill the microorganism.