Epidemiology of Zucchini yellow mosaic virus in cucurbit crops in a remote tropical environment

• Published in: Virus research 2020-05, Vol.281, p.197897-197897, Article 197897
• Main Authors: Clarke, Rebecca, Webster, Craig G., Kehoe, Monica A., Coutts, Brenda A., Broughton, Sonya, Warmington, Mark, Jones, Roger A.C.
• Format: Article
• Language: English
• Subjects: Alternative hosts; Aphid trapping; Aphid vectors; Cucurbit crops; Cucurbit cultivar reactions; Data collection blocks; Epidemic drivers; Epidemiology; Infection reservoirs; Integrated disease management; Phylogeny; Spatiotemporal spread patterns; Tropics; Zucchini yellow mosaic virus
• ISSN: 0168-1702; 1872-7492
• DOI: 10.1016/j.virusres.2020.197897

•Critical knowledge of tropical Zucchini yellow mosaic virus (ZYMV) epidemics revealed.•Comprehensive Integrated Management strategy for tropical ZYMV epidemics devised.•ZYMV spread within data collection blocks resembled spread in commercial cucurbit crops.•Aphid vector numbers caught varied widely with trap location and time of year.•No evidence of new ZYMV variants introduced since 1996 obtained. In the remote Ord River Irrigation Area (ORIA) in tropical northwest Australia, severe Zucchini yellow mosaic virus (ZYMV) epidemics threaten dry season (April-October) cucurbit crops. In 2016–2017, wet season (November-March) sampling studies found a low incidence ZYMV infection in wild Cucumis melo and Citrullus lanatus var. citroides plants, and both volunteer and garden crop cucurbits. Such infections enable its persistence in the wet season, and act as reservoirs for its spread to commercial cucurbit crops during the dry season. Tests on 1019 samples belonging to 55 species from 23 non-cucurbitaceous plant families failed to detect ZYMV. It was also absent from wild cucurbit weeds within sandalwood plantations. The transmission efficiencies of a local isolate by five aphid species found in the ORIA were: 10 % (Aphis craccivora), 7% (A. gossypii), 4% (A. nerii), and 0% (Rhopalosiphum maidis and Hysteroneura setariae). In 2016–2017, in all-year-round trapping at five representative sites, numbers of winged aphids caught were greatest in July-August (i.e. mid growing season) but varied widely between trap sites reflecting local aphid host abundance and year. Apart from one localised exception in 2017, flying aphid numbers caught and ZYMV spread in data collection blocks during 2015–2017 resembled what occurred commercial cucurbit crops. When ZYMV spread from external infection sources into melon blocks, its predominant spread pattern consisted of 1 or 2 plant infection foci often occurring at their margins. In addition, when plants of 29 cucurbit cultivars were inoculated with an ORIA isolate and two other ZYMV isolates and the phenotypes elicited were compared, they resembled each other in overall virulence. However, depending upon isolate-cultivar combination, differences in symptom expression and severity occurred, and one isolate caused a systemic hypersensitive phenotype in honeydew melon cvs Estilo and Whitehaven. When the new genomic RNA sequences of 19 Australian isolates were analysed, all seven ORIA isolates fitted within ZYMV phylogroup B, which al