Phytophthora nicotianae is the predominant Phytophthora species in citrus nurseries in Egypt

Phytophthora root rot is considered to be the most destructive disease to citrus production in Egypt. Phytophthora species are generally present in citrus nurseries, where soil pots containing the survival propagules are considered responsible for their spread into new orchards. The goal of this study was to investigate the distribution and seasonal variation of Phytophthora species in soil and feeder roots in two Egyptian citrus nurseries, characterized by different management, and to identify Phytophthora species associated with root rot. Soil and root samples were collected at monthly intervals from Sour orange and Volkameriana lemon rootstocks during March-July period. The inoculum density of Phytophthora species, and the percentage of infected feeder roots, were estimated using the plate dilution method in conjunction with selective media. Phytophthora isolates were identified according to their morphological characteristics and on the basis of the ITS regions of the rDNA. Phytophthora nicotianae was the predominant isolated species, followed by P. citrophthora and P. palmivora. Phytophthora nicotianae was detected in both nurseries, while P. citrophthora and P. palmivora were recovered only in one nursery. Inoculum density of Phytophthora species fluctuated during spring and summer according to the environmental conditions, rootstock, and nursery management practices