Permalink : http://hdl.handle.net/2115/73697

KEYWORDS : Phytophthora infestans;sample collection;isolation;potato late blight

Our new direct zoosporangia sampling (DZS)method was compared with the conventional newspaper bag method as an easy technique for sampling and isolating Phytophthora infestans. Field tests were conducted in the Tokachi region,Hokkaido,Japan,in 2016 and 2017. With the new method,zoosporangia on the lower side of diseased leaves in the field were brought into direct contact with selective medium (Rye-B agar with rifampicin, ampicillin sodium and nystatin at concentrations of 25,100 and 50μg/mL,respectively). The collected zoosporangia on the agar were then transported to the laboratory under cool conditions for isolation. With the paper bag method, the diseased leaves collected in the newspaper bags were kept in the laboratory for 0, 1, 2 or 3 days. Then, the zoosporangia on each lesion were transferred to selective medium to isolate P. infestans. For the 500 samples collected with the two methods, there was no significant difference in the number of successful isolations. The new DZS method is comparable to the conventional paper bag method. In addition, it is not necessary to perform initial subcultures in the laboratory with the DZS method. Therefore, this simplified method saves much labor and time when collecting isolates of P. infestans.