Iris yellow spot virus is a detrimental, disease-causing tospovirus in onion crops. It has been evolving since years to adapt to the host and environmental conditions which makes it a substantial threat for onion growers. As per virologists from Washington State University (WSU), onions evaluated from a field in Grant County were heavily infected with the Iris yellow spot virus, eventually killing the plants and yield. The disease was reported to spread within the major onion growing counties in the span of a mere few years, significantly impacting onion plantation. 

What Complicates the Management of Iris Yellow Spot Virus? 

Iris yellow spot virus was named after its original host, starting with local infections in the early 1900s, now it has managed to become a worldwide threat to onion productivity causing heavy losses. It infects number of crops from Allium species found globally, including major European countries, India, Japan, Australia, and some countries in Africa and America. The virus was found infecting onion crops in southern Idaho and Oregon in the 1900s as well, and the infection rate raised rapidly leaving scientists with no clue about the reason behind that sudden resurgence. The infection starts by weakening the seed-bearing stems of onion plants. As the pathogenesis grows further, the stems fall off and the seeds are damaged and dislodged prematurely. The damage doesn’t end here; the virus further affects the photosynthetic capacity of onion plants. Reduction in the photosynthetic activity causes shrinkage of onion bulbs, thus affecting yield greatly. 

It was found that Iris yellow spot virus is also exclusively spread by onion thrips (Thrips tabaci) which act as vector in the transmission process. Viruses spreading via vectors tend to adhere to the body of the insect-pests and get transferred from infected to healthy crops. A researcher from WSU involved in the in-depth investigation of this virus confirmed that thrips play a crucial role in transmitting Iris yellow spot viruses between onion crops. This makes controlling the virus even more challenging because the rate of infection gets higher than control. Consequently, the growers shall be required to effectively manage onion thrips at the same time. 

Genetics Behind the Infectivity 

Researchers at Washington State University examined why the virus evolves quickly and spreads even rapidly using a molecular method called genetic fingerprinting. It was found that Iris yellow spot virus has two different strains. A postdoctoral student, Afsha Tabassum, studied hundreds of genetic sequences for the virus and concluded that the virus is using genetic recombination and mutation techniques to evolve. It was interesting to find out that one of the strains was predominantly attacking onion crops in the US, whereas the second strain infected Allium crops in other parts of the world. The researchers from WSU also compared the mutagenicity of the virus with COVID-19 variants. They explained that the viruses, despite being host-specific, are prone to evolving continuously to compete and survive. Though speed of the evolution may vary from one virus to another. 

Thus, it is evident that viruses are evolving, being spread through various modes, destroying important crops, and growers need multifaceted management approaches to tackle them. The research conducted by WSU scientists using genetic fingerprinting also led to important findings which can be crucial in devising strain-specific control methods and management techniques. Read the full article on Iris yellow spot virus at https://international-pest-control.com/wordpress/destructive-onion-virus-evolving-and-spreading/ 

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