Density of Pythium zingiberum Oospores in Relation to Infection of Chenopodium quinoa Seedlings Density of Pythium zingiberum Oospores in Relation to Infection of Chenopodium quinoa Seedlings

The infectivity tests were repeated and the average results obtained indicated that more than 1×10^4 oospores per gram oven dry soil (OPG) caused damping-off of 80% of Chenopodium quinoa seedlings. About 20% damping-off occurred with 1×10^3 OPG. With 1×10^2 OPG the average was 6%, and penetrating mycelium and oospores were easily recognized. Neither penetration nor disease incidence was found with 1×10 OPG. Thus, the minimum number of oospores capable of inducing disease was estimated to be 10-1×10^3/g oven dry soil. The fact that P.zingiberum needs much more oospores than P.butleri to induce disease may be connected with lower germinability of oospores of the former.

The infectivity tests were repeated and the average results obtained indicated that more than 1×10^4 oospores per gram oven dry soil (OPG) caused damping-off of 80% of Chenopodium quinoa seedlings. About 20% damping-off occurred with 1×10^3 OPG. With 1×10^2 OPG the average was 6%, and penetrating mycelium and oospores were easily recognized. Neither penetration nor disease incidence was found with 1×10 OPG. Thus, the minimum number of oospores capable of inducing disease was estimated to be 10-1×10^3/g oven dry soil. The fact that P.zingiberum needs much more oospores than P.butleri to induce disease may be connected with lower germinability of oospores of the former.