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Comparison the effects of Chrysanthemum stunt viroid, Hop stunt viroid and Citrus exocortis viroid on tomatoes using Agro-inoculation

Ying-Huey Cheng: Taiwan Agricultural Research Institute

<div>Viroids are known as the smallest self-replicating RNAs that infect plants. Symptoms caused by viroids vary depending on the species and varieties of the hosts. Three tomato-infecting viroid, <em>Chrysanthemum stunt viroid</em> (CSVd), <em>Hop stunt viroid</em> (HSVd) and <em>Citrus exocortis viroid</em> (CEVd) have been reported in chrysanthemum or citrus but not on tomato in Taiwan. Aiming in assessing the impact of the above three viroids on popular tomato varieties in Taiwan, the <em>partial</em><em> </em>tandem<em> </em><em>repeat</em> clones CS, HS and CE, corresponding to the CSVd-t (LC090813, tomato isolate), HSVd-c (X00524, cucumber isolate) and CEVd-t-10 (EF494692, tomato isolate) were synthesized, cloned into Ti plasmid (pCAMBIA1302) and transformed to <em>Agrobacterium tumefaciens</em>. Activity assay of the three clones were performed by agro-inoculated to tomato with 10<sup>7 </sup>cells per inoculation. Four tomato varieties including 2 big-fruit tomatoes (Farmer 301 and Hui-Jiao) and 2 cherry tomatoes (Kim-Ying and Jade girl) were used as host analysis in this study. The inoculated plants were examined and confirmed as infected by viroid using the reverse transcription-PCR method forty days after inoculation. More than 90% of the tested plants were detected with the corresponding viroid. All plants of four tomato varieties infected with the clone CS and HS were symptomless. Contrary to the previous description, plants of the 4 tomato varieties infected with the clone CE had significant symptoms such as leaf deformation and growth retardation. When the infected tomato plant was used as inoculum, the host range test was confirmed by mechanical inoculation to give the same results. Both CSVd and HSVd are seed-transmission with 2.3% and 1.2%, respectively. When the plants infected with CEVd were unable to produce fruits and seeds, and the four varieties were the same.</div>