Interaction between Likubin Bacterium and Phytophthora parasitica in Citrus Hosts

Abstract

Infection with Likubin bacterium (LB) followed by Phytophthora parasitica increased the mortality of sour orange and pummelo seedlings, and enhanced the P. parasitica-induced root rot in all the four types of citrus tested. The LB-induced enhancement of root infection by P. parasitica was apparent within 1 h of exposure to zoospore suspension. The enhancement of P. parasitica-induced root rot was affected by the infection sequence. Inoculation of sour orange seedlings with LB before P. parasitica was more effective in increasing P. parasitica-induced root rot than LB and P. parasitica concomitantly or LB after P. parasitica. Grafting P. parasitica susceptible scions of ponkan (Citrus reticulata) onto P. parasitica-tolerant rootstocks of sour orange greatly increased the susceptibility of rootstocks to P. parasitica. Results also demonstrate the enhancement of LB-induced symptoms by P. parasitica in citrus plants.