DISTRIBUTION, POPULATION DENSITY, AND VIRULENCE OF CITRUS GUMMOSIS AND BROWN ROT IN MAZANDARAN PROVINCE

A general surveys were conducted in Mazandaran citrus groves for the presence of Phytophthora species causing citrus gummosis. Soil samples and infected citrus tissues were collected and assayed using baiting and selective medium. Phytophthora citrophthora and P. nicotianae were detected in all of the citrus orchards and their distribution was mapped. The soil population of each species was also determined. Eighty two and 86% of the orchards were infested respectively with P. citrophthora and P. nicotianae with average over 10 propagules /g soil.The virulence of five isolates of each species to root of 1-year-old citrange, citromelo, Shahsavar orange, and sweet lime was examined. Data analysis of fresh weight of root and stem, and disease index in citrange revealed three groups including control, P. nicotianae, and P. citrophthora isolates, which the that third group was significantly more virulent than the second group. Data analysis of fresh weight of root and stem in citromelo and Shahsavar orange did not show significant differences between P. nicotianae, and P. citrophthora isolates. On the basis of disease index data of citromelo and Shahsavar orange, P. citrophthora isolates were more virulent than P. nicotianae isolates. Data analysis of fresh weight of root and stem and disease index in sweet lime did not show significant differences between P. nicotianae, and P. citrophthora isolates.