Sporangium Germination of Peronophythora Litchii, The Causal Organism of Litchi Downy Blight

SUMMARY

Litchi downy blight (name proposed) is induced by Peronophythora litchii. The fungus causes fruit rot in litchi (Litchi chinensis). The cardinal temperatures for growth are 12, 28, and 32 C and for sporangium germination are 12, 28, and 36 C. The sporangia germinate by normal germ tube (direct germination) on V-8-juice agar, and by releasing zoospores (indirect germination) in water. On 2% water agar with 0–10% dextrose, more sporangia germinate directly by a normal germ tube and by production of secondary sporangia as dextrose concentration increases. As dextrose concentration decreases, more sporangia germinate by a “thin” germ tube. Germination by zoospores remains constant. Percent germination decreases as the culture ages. The chilling effect on zoospore release is most evident at 16 C for 30 min when the culture was grown at 26 C and at 12 C for that grown at 16 C. The morphology of the fungus is described briefly.