Occurrence of Downy Leaf Spot on Juglans regia Caused by Microstroma juglandis in Korea

Lee, Sang Hyun; Lee, Seung Kyu; Park, Ji Hyun; Cho, Sung Eun; Shin, Hyeon Dong

Research in Plant Disease 2011;17(3):386-390.
Published online December 30, 2011.

Microstroma juglandis에 의한 호두나무 흰곰팡이병 발생

이상현, 이승규, 박지현, 조성은, 신현동

Occurrence of Downy Leaf Spot on Juglans regia Caused by Microstroma juglandis in Korea

Sang Hyun Lee, Seung Kyu Lee, Ji Hyun Park, Sung Eun Cho, Hyeon Dong Shin

Abstract

In June 2011, walnuts (Juglans regia) from orchards in Kimcheon and Muan, in southern Korea, were found to exhibit downy mildew-like symptoms of a foliar disease. Whitish polygonal efflorescence was produced on the abaxial surface of affected leaves and discolored light green blotches on the corresponding adaxial surfaces. In the later stage of disease development, diseased tissues collapsed and became necrotic. Based on morphological and cultural characteristics, the causal fungus was identified as Microstroma juglandis. The sequence of ITS rDNA of the present isolate showed 100% similarity with those of M. juglandis obtained from GenBank databases, thus confirming its identity. Pathogenicity tests were conducted on leaves of walnut seedlings, fulfilling Koch`s postulates. The disease has been previously reported in North America, Europe, Oceania and some western Asia. This is the first report of downy leaf spot on walnuts in East Asia.

Key Words: Downy Leaf spot, Juglans sinensis, White mold