An-Najah Staff

During a survey extending over 8 months, Phytophthora strains were isolated from two Citrus plantations in the West Bank contrasting in agricultural management and climate (Jordan Valley and Tulkarem regions). This was the first survey for Phytophthora on Citrus in this region. Four techniques were used for isolations (soil dilution, direct isolation from plant material, and baiting soil with Citrus leaf discs or lupin radicles). Species were identified using morphological and growth characteristics. Only two species were detected, namely Phytophthora citrophthora and P. nicotianae. Highest numbers of P. citrophthora and P. nicotianae isolates were obtained by soil dilution and Citrus baiting, with the former discriminating in favour of P. nicotianae. Direct isolation from plant material and lupin baiting were the least successful recovery methods. Differences in spatial distribution of isolates could be related to differing agricultural management and geographical features of the plantations. Although the species distribution was similar in the two plantations, the total number of isolates recovered differed significantly between subsites in the Jordan Valley plantation. The number of isolates obtained from sequential soil samples also varied and was generally higher in samples taken in the cooler, wetter winter months. Significantly more isolates were found in the Tulkarem plantation. Irrigation at Tulkarem was by flooding, while spot irrigation was used in the Jordan Valley. The longer established Tulkarem plantation contained a mixture of Citrus cultivars unlike the newer Jordan Valley orchard.