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Relationship between Stemphylium vesicarium and onion thrips (Thrips tabaci) in the development of Stemphylium leaf blight disease

Ashley Leach: Cornell University

<div>Stemphylium leaf blight of onion (caused by <em>Stemphylium vesicarium)</em> and onion thrips (<em>Thrips tabaci</em>) are two common causes of leaf defoliation of onion in New York. Onion thrips have previously shown to interact synergistically with other pathogens which exacerbate plant disease. However, the potential relationship between onion thrips and Stemphylium leaf blight is unknown. In a series of controlled laboratory experiments, the relationship between thrips feeding and movement on the development and severity of Stemphylium leaf blight disease were examined. Onions (cvs. ‘Avalon’ and ‘Ailsa Craig’) with varying levels of thrips damage (‘no damage’, ‘low damage’, or ‘high damage’) were inoculated with <em>S. vesicarium</em>. Pathogen colonization and leaf dieback were measured after two weeks. In the transmission assays, thrips were exposed to <em>S. vesicarium</em> spores for 30 min., and then transferred to onion leaves where plants were monitored for disease development. Initial results from these trials revealed that thrips feeding increased <em>S. vesicarium</em> colonization of onion leaves, and increased leaf dieback. Additionally, onion thrips were capable of transferring <em>S. vesicarium</em> spores to onion plants (albeit at a low frequency 5-15% of the time). These results suggest that increased thrips control may reduce Stemphylium leaf blight disease, and should be investigated in the field.</div>