Phytophthora citricola, a Causal Agent of Jujube (Zizyphus jujuba) Fruit Rot

대추 역병균의 Phytophthora citricola의 동정

Phytophthora rot on jujube fruit has occurred at several cultivation areas in Kyung-buk and Kyung-nam provinces. Symptoms consisted of brownish to reddish rot on fruits resulting in early drop or mummification. The causal fungus isolated from infected fruits and adjacent leaf stalks was identified as Phytophthora citricola, which has never been reported in Korea. Sporangia were semi-papillate, noncaducous and highly variable in shapes. Plerotic oospores with paragynous antheridia were abundant is single cultures. Sporangia of two isolates were measured as 38-76$\times$20-40 ${\mu}{\textrm}{m}$ and averaged 51.4$\times$27.0 and 55.6$\times$36.0 ${\mu}{\textrm}{m}$. Oogonia were ranged from 26 to 36 ${\mu}{\textrm}{m}$ and averaged 31.3 and 32.0 ${\mu}{\textrm}{m}$. Colony pattern was slightly radiated with sparse aerial mycelia on common media. Minium, optimum and maximum temperatures for mycelial growth were recorded at 7, 25, and 32$^{\circ}C$, respectively. Among tested media, 10% V8A was the best and $25^{\circ}C$ was better than 15$^{\circ}C$ for oospore formation of the fungus. The jujube isolates of P. citricola were readily differentiated from other closely related species in the genus, namely; P. nicotianae, P. citrophthora, P. cactorum, P. capsici, and P. plalmivora on the basis of PCR-RFLP of r-DNA. The fungus showed strong pathogenicty to jujube, apple, pear, orange, persimmon and eggplant, and relatively weak to citron, tomato, pepper and cucumber. In this study, P. citrocola is firstly identified and jujube fruit rot caused by the fungus is recorded as a new disease in Korea.