Screening winter-sown onion entries for iris yellow Spot virus tolerance

Abstract

Identification of resistant or tolerant onion (Allium cepa L.) cultivars is crucial for the development of integrated management strategies for Iris yellow spot virus (IYSV). Exclusively vectored by onion thrips (Thrips tabaci), IYSV is a potentially devastating tospovirus of onion that has been confirmed to be present in 15 countries all over the world. In this study, 18 winter-sown onion entries were screened for IYSV symptom expression over two seasons. Over the growing season, straw-colored, necrotic lesions typical of IYSV infection were observed and rated for disease severity. Entries, NMSU 03-52-1, NMSU 04-41, NMSU 04-44-1, and 'NuMex Jose Fernandez;, exhibited fewer symptoms than many other entries tested. 'Caballero;, NMSU 04-57-1, NMSU 04- 78-1, and 'Cimarron; exhibited more symptoms. Disease progression over time was rapid for entries exhibiting more symptoms and slow for entries exhibiting fewer symptoms. Enzyme-linked immunosorbent assay (ELISA) optical densities correlated poorly with the s erity of disease symptoms. Trends in the disease progression over time emphasize the importance of rating IYSV symptoms late in the crop;s development and to search for delayed disease progression rather than early symptom expression to determine IYSV susceptibility. © 2000 IEEE.