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Effect of Benzothiadiazole on Transmission of X-Disease Phytoplasma by the Vector Colladonus montanus to Arabidopsis thaliana, a New Experimental Host Plant

Colladonus montanus (Van Duzee), a leafhopper vector of X-disease phytoplasma (Xp), efficiently transmitted the pathogen to Arabidopsis thaliana Columbia wild type. During transmission trials, the phytoplasma was inoculated into 22-, 34-, and 40-day-old plants. Phytoplasma infections were confirmed by polymerase chain reaction (PCR) using primers specific for X_p Symptoms in X_p-positive A. thaliana were overall stunting and reduced or no fruit (silques). All symptom-free plants were PCR negative. Leafhopper nymphs free of X_p that fed on diseased A. thaliana acquired and transmitted X_p to celery plants, a diagnostic host, causing typical X-disease symptoms. Foliar spray applications of the plant resistance elicitor benzothiadiazole (BTH) to A. thaliana 1 week before phytoplasma inoculation significantly reduced phytoplasma infection, ranging from an infection rate of 73.7% for untreated plants to 50 and 35% for plants treated with 1.2 and 4.8 mM BTH, respectively. Vector leafhoppers survival was significantly reduced on BTH-treated A. thaliana compared with leafhoppers on nontreated plants, suggesting that systemic acquired resistance in this plant may have some detrimental effect on the leafhopper C. montanus.