배나무 검은무늬병균(Alternaria kikuchiana Tanaka)에 병원성분화와 저항성품종의 이병화

Differentiation in Pathogenicity of Alternaria kikuchiana Tanaka, Black Spot Fungus of Pear, and Conversion of Resistant Varieties into Susceptible ones

전남 나주지방에서 만연하고 있는 검은무늬 병 유사증상을 조사한 결과는 다음과 같다. 1. 병원균은 Alternaria kikuchiana Tanaka로 동정되었다. 2. 5월 하순부터 발병되기 시작하여 6월 하순$\~$7월상순에 가장 심하였고 9월 상순에 다시 증가하였다. 3. 이병은 조사품종들의 성엽에 발생하였으나 20세기에서만 유엽에 많이 발생하였다. 5. 이 병은 나주시험장에 있는 거의 모든 품종에 발병하였는데 종래 저항성품종으로 알려진 신흥, 만3길등은 가장 심한 발병을 보였고 이병성품종으로 알려진 조옥, 박다청등은 약간 발병하거나, 전혀 발병하지 않았다. 6. 이상의 결과로 미루어 보아 검은무늬병균에 병원성의 분화가 일어난 것으로 판단된다.

Recently, a symptom similiar to black spot caused by Alternaria kikuchiana on the pear leaves is prevailing in Naju, Chonnam Province. This experiment was conducted in order to clarify causal agent and to survey present status on it. Disease lesions on the leaves were brown or black brown in color, circle or irregular circle in shape, $2\~6mm$ in diameter, and faintly zonal. Central part of lesions was gradually changed to greyish-white. The causal fungus was identified as Alternaria kikuchiana Tanaka causing black spot of pear reported previously on variety I-sib-se-gi (Nijisseki) of pear. However, this disease differed from that of typical black spot reported already in some aspects; It occurred more highly on matured leaves than on young ones. And it occurred severely in varieties Shin-heung, Shin-ko, Man-sam-gil(Okusankichi) etc. which have been reported as resistant varieties, while slightly in varieties Cho-ok(Hayadama), Park-da-cheung (Hakadahare) etc. which have been known as susceptible ones. From the results described above, it is considered that this disease is due to the differentiation in pathogenicity of Alternaria kikuchiana Tanaka in that area.