Control of citrus tristeza virus in neck orange by inoculation with mild strain

Control of citrus tristeza virus in neck orange by inoculation with mild strain
การควบคุมโรคทริสเตซาในส้มจุกโดยการปลูกเชื้อสายพันธุ์ไม่รุนแรง

Ratana Sdoodee, Assoc. Prof., D. of Pest Management, F. of Natural Resources, PSU.
Mongkol Lim, Assoc. Prof., D. of Plant Sci., F. of Natural Resources, PSU.
Suparp Kietthubthew, D. of Stomatology, F. of Dentistry, PSU.

Grant : Government Budget
Published : Research Report
Key words : citrus tristeza virus, neck orange, inoculation with mild strain

Total of 64 tristeza virus isolates obtained from Neck orange, Siam mandarin, Shogun mandarin, Pomelo, Calamondin, and Acid lime were collected from Chiang Rai, Janthaburi, Pratumthani, Nakorn Srithamarat, and Songkhla. Sixty-three isolates were isolated by graft transmission and 1 isolates by insect transmission. Among these, 28 isolates induced mild vein clearing symptom on index plant (Acid lime).

Two monoclonal antibodies, McAb 10E3 and McAb 4H6 specific to mild and severe strains of citrus tristeza virus (CTV), respectively were used to discriminate the mild strain. We found that one isolate of CTV from Neck orange No. 3/3 reacted to McAb 4H6 but not to McAb 10E3. Two isolates from Neck orange and Shogun marin reacted to both monoclonal antibodies. However, the isolate reacted to McAb 4H6 only caused severe symptom on Neck orange.

Analysis of double stranded RNA of CTV extracted from Neck orange. Calamondin and Pomelo indicated that bands of CTV-ds RNAs from Neck oranges and Calamondins were similar but they were different from CTV-ds RNAs extracted from Pomeloes. When ds RNA of CTV showing mild symptom in the Neck orange No. 3/3 was compared to other isolates from Neck orange, it was found that they were identical. Incontrast, immunogold labelling using CTV polyclonal antibodies showed that number of gold particles deposited on CTV particles trapped from Neck orange No. 3/3 was lower than the number of gold particle associated with CTV particles from other isolates although the same concentration of the antibodies were applied.

Among 28 isolates of CTV showing mild symptom in Acid lime, only 1 isolate (the isolation from Neck orange 3/3) was selected according to evidence from immunogold labelling to be used for preimmunization against the severe strain of CTV. However, in this experiment we failed to preinoculate CTV isolate from Neck orange 3/3 into healthy Neck orange seedling by grafting. Therefore, we could not evaluate protection ability of this isolate to the severe strain.

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