Seasonal Changes in Extent of Colonization of Citrus Root Tissue by Phytophthora citrophthora and P. parasitica

Abstract

For 24 consecutive months, root pieces were collected from field -grown Lisbon lemon trees established on Citrus aurantium (sour orange), C. jambhiri (rough lemon), and C. volkameriana rootstocks. Root segments were wounded, inoculated with Phytophthora citrophthora or P. parasitica, and incubated for 96 hr in moist chambers. Smaller lesions developed during Jan -Feb than during Jul-Oct on root pieces of all tested rootstocks inoculated with P. citrophthora as well as root pieces of C aurantium inoculated with P. parasitica. Apparently there is a seasonal variation in the susceptibility of citrus rootstocks to colonization by Phytophthora. This information could be useful for more effective timing of fungicide applications.