Iris yellow spot virus (Iris yellow spot).

In 1981, de Avila et al. (1981) described a disease characterized by chlorotic and necrotic, eye-like or diamond-shaped lesions on onion scapes (referred to as 'sapeca') in southern Brazil. In 1989, Hall et al. (1993) observed a very similar disease in onion in the USA and detected a tospovirus, which was later shown by Moyer et al. (1993) to be Iris yellow spot virus on the basis of molecular and serological data. In 1998, a new tospovirus was isolated and characterized in the Netherlands from infected iris and leek and named Iris yellow spot virus (IYSV) (Cortês et al., 1998). This virus was subsequently found naturally infecting onion in several major onion-producing states of the USA and around the world (for reviews, see Gent et al., 2006 and Pappu et al., 2009). Gera et al. (1998b) reported that IYSV was responsible for a 'straw bleaching' disease on onion in Israel. In 1999, a 'sapeca' isolate from Brazil was identified as IYSV on the basis of biological, serological and molecular data (Pozzer et al., 1999). In Israel, Kritzman et al. (2000) reported natural IYSV infection of lisianthus grown in the field. IYSV has now been endemic in south-western Idaho and eastern Oregon in onion, leek and chive seed production fields for over 10 years. Losses caused by IYSV can reach 100% in onion crops, for example, in Brazil (Pappu et al., 2009). However, studies in the Netherlands in 2008 showed that latent infections of IYSV were common in onion crops but did not cause economic damage (NPPO of the Netherlands, 2008). Iris yellow spot represents an immediate and serious threat to sustainable and productive onion cropping systems around the world, and the recent detection of this disease in numerous onion-producing countries demonstrates that the disease is spreading rapidly in a range of environments. IYSV is on the EPPO Alert list (http://www.eppo.org/QUARANTINE/Alert_List/alert_list.htm).

DETECCIÓN DEL IRIS YELLOW SPOT VIRUS EN EL CULTIVO DE CEBOLLA EN ZACATECAS, MÉXICO

El virus de la mancha amarilla del iris (IYSV) es la enfermedad viral de mayor importancia para los cultivos de ajo y cebolla en Zacatecas, México. A finales de mayo de 2010 se encontraron lesiones amarillentas en forma de diamante en hojas y tallo floral de plantas de cebolla en parcelas comerciales, localizados en los municipios de Loreto, Villa de Cos, Sain Alto, Villanueva, Calera de V. R. y Enrique Estrada pertenecientes al estado de Zacatecas. La prueba DAS-ELISA mostró resultados positivos para este virus en las muestras procedentes de diferentes municipios. Thrips tabaci el único vector conocido del IYSV se encontró en las parcelas comerciales muestreadas, aunque la presencia de Frankliniella occidentalis también fue reconocida en una parcela comercial de cebolla, cuyas muestras resultaron positivas a IYSV. No se encontró diferencia entre la altura, número de hojas, peso y diámetro de bulbo de plantas sin lesiones y aquellas con diferente número de lesiones de IYSV.

Importance of Transplanted Onions Contributing to Late-Season Iris yellow spot virus Epidemics in New York

Iris yellow spot virus (IYSV) is an economically significant tospovirus of onion transmitted by onion thrips (Thrips tabaci Lindeman). IYSV epidemics in onion fields are common in New York; however, the role of various habitats contributing to viruliferous onion thrips populations and IYSV epidemics is not known. In a 2-year field study in New York, the abundance of dispersing onion thrips, including those determined to be viruliferous via reverse-transcriptase polymerase chain reaction, was recorded in habitats known to harbor both IYSV and its vector. Results showed that viruliferous thrips were encountered in all habitats; however, transplanted onion sites accounted for 49 to 51% of the total estimated numbers of viruliferous thrips. During early to midseason, transplanted onion sites had 9 to 11 times more viruliferous thrips than the other habitats. These results indicate that transplanted onion fields are the most important habitat for generating IYSV epidemics in all onion fields (transplanted and direct-seeded) in New York. Our findings suggest that onion growers should control onion thrips in transplanted fields early in the season to minimize risk of IYSV epidemics later in the season.

Potential factors contributing to the decline of Iris Yellow Spot Virus in organically grown onion crops in Canterbury and Hawke's Bay over three years

The Tospovirus Iris yellow spot virus (IYSV), transmitted by thrips (predominantly Thrips tabaci), was first recorded in New Zealand in 2007. In March 2015, symptoms of the virus were relatively widespread in an organically managed onion crop in Canterbury. Onion plants were sampled for the presence of T. tabaci adults and larvae and for IYSV symptoms on an organically managed farm in Canterbury in 2014-2015, 2015-16 and 2016-17, and on a similar farm in Hawke's Bay in 2014-2015 and 2015-16. An immunoassay was used to confirm the presence of IYSV in some symptomatic plants. In Canterbury, IYSV symptoms were less apparent in 2015-16 and no symptoms were observed in 2016-17. No IYSV symptoms were observed in the Hawke's Bay onion crop, despite relatively high T. tabaci numbers. The virus symptoms declined from when they were first observed in March 2015 to undetectable levels in 2016-17 in Canterbury, which may be attributed to crop location, fewer thrips and the absence of a disease reservoir in volunteer Allium cepa plants or other hosts.