Transmission of the Huanglungbin Agent from Citrus to Periwinkle by Dodder

Abstract

During 1981-1985, several experiments were conducted to transmit the citrus huanglungbin agent from citrus to citrus, periwinkle, cabbage, cucumber, tobacco and and Solanum nigmm by means of Diaphorina citri, Cuscuta campestris, C. japonica, and graft inoculations. Diaphorina citri transmitted huanglungbin agent to citrus seedlings, but not to the other eight plant species tested. The huanglungbin agent was transmitted to periwinkle by C. campestris but not by C. japonica. Of the 25 periwinkle plants tested, 96% of the periwinkle plants developed yellowing symptoms in 3-6 months after inoculation. Observations by electron microscopy of thin sections of leaf veins of the inoculated citrus and periwinkle plants revealed the presence of bacteria-like organisms (BLO's) in the sieve tubes. These BLO's were ultrastructurally and morphologically similar to those found in tissues of greening affected citrus and periwinkle plants. The titre of BLO in the sieve tubes of the affected periwinkles was higher than that of citrus. Subsequent transmission from periwinkle to periwinkle was successful only by graft inoculation.