Archive for the ‘tomato yellow leaf curl virus’ Category

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crumplevirus UGA CAES
Cucurbit leaf crumple virus, a disease carried by whiteflies, infects vegetable plants like squash.

Whitefly influx puts hurt on Georgia vegetables

High populations of whiteflies over the past few years had a tremendous impact on Georgia’s vegetable crops in both the spring and the fall.

Julie Jernigan | Oct 03, 2017

Summer may have ended, but Georgia’s silverleaf whitefly infestation has not.

Timothy Coolong, University of Georgia Cooperative Extension vegetable specialist, researches whitefly management in an effort to prevent the pest from infecting Georgia’s vegetable crops with viral diseases, like cucurbit leaf crumple virus and tomato yellow leaf curl virus.

Whiteflies are found on vegetable plants, like yellow squash, zucchini and green beans. Last fall, Georgia vegetable growers lost 40 to 50 percent of their yellow squash production. Green bean growers saw similar production losses due to the cucurbit leaf crumple virus, a disease carried by whiteflies.

Also known as “Aleyrodidae,” whiteflies are tiny, winged insects often found on the underside of leaves. They leave behind a tacky substance called “honeydew” that prevents plants from carrying out photosynthesis and causes fungal infections.Coolong and other scientists on the team tested several treatments on yellow squash and zucchini in an attempt to make the plants grow fast enough to tolerate the virus, which might prevent whiteflies from swarming. One application focuses on high fertilizer rates and another uses gibberellic acid to promote foliar development early in the growing process.

“Researching different control methods for whiteflies is important, not only because of the direct damage they can do to crops, but to stop the viruses that they can spread,” Coolong said.

Early control is key to prevention of the viruses spread by whiteflies. Farmers must proceed with caution in working on some of the most susceptible crops because of the losses that have been sustained the past two years, according to Coolong.

“Squash alone is close to a $60 million industry (in Georgia). We suffered significant losses in the fall of 2016 and are seeing losses again this fall. Growers need to have a plan for management before the seed emerges or a plant comes out of the greenhouse,” Coolong said. “Whiteflies can be very devastating.”

Whiteflies thrive in warm, humid climates, and they reproduce quickly. The warmer-than-normal winter that Georgia experienced last year helped whitefly populations multiply. In normal years, Coolong recommends using insecticides as a management tool. Given the current conditions in Georgia, he warns growers that they may not completely wipe out the whitefly population with insecticides alone.

“In a normal year, insecticides would be very effective, but this year the whitefly population is high,” Coolong said. “Even if a product works and kills 90 percent of the population in a field, they will return because of how fast they can reproduce, and all the plants surrounding those fields serve as hosts for the whitefly.”

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Aug 22,2014



A team of virologists and plant geneticists at Wageningen UR has demonstrated that when tomato plants contain Ty-1 resistance to the important Tomato yellow leaf curl virus (TYLCV), parts of the virus DNA (the genome) become hyper-methylated, the result being that virus replication and transcription is inhibited. The team has also shown that this resistance has its Achilles heel: if a plant is simultaneously infected with another important (RNA) virus, the Cucumber mosaic virus (CMV), the resistance mechanism is compromised.

Antiviral defence via RNAi
Plant defence to viruses usually depends on RNA interference (RNAi). The genetic material of many viruses consists of RNA. A complex process in the plant causes the virus RNA to be chopped up into pieces, which means the virus can no longer multiply. In contrast to most other disease-causing plant viruses, the genetic material in TYLCV is DNA, not RNA. Therefore antiviral RNAi defence to these viruses has to happen somewhat different.

TYLCV is one of the most economically important plant viruses in the world; for this virus a number of resistance genes (Ty-1 to Ty-6) are available to commercial plant breeders. In 2013 the researchers in Wageningen succeeded in identifying and cloning the Ty-1 gene, which happened to present a member from an important class of RNAi-pathway genes. This led to a publication in PLoS Genetics. Their recent publication in the journal PNAS shows that although Ty-1 resistance depends on RNAi, instead of the genetic material being chopped up, it is being ‘blocked’ by methylation of the virus DNA.

No cross protection
A well-known phenomenon in the plant world is the ‘immunisation’ of plants by infecting them with relatively harmless viruses. The latter ensures that the defence mechanisms in plants are activated and provide ‘cross protection’ against more harmful, related viruses.

To their great surprise, the Wageningen researchers discovered that infection with CMV, a virus that contains RNA as genetic material and that, as a result, is not affected by the Ty-1 resistance mechanism, actually compromised resistance to the TYLCV virus. According to the researchers, this is a warning to plant breeders. The use of the Ty-1 gene does provide resistance, but the mechanism will be at risk in plants grown in greenhouses and fields if the plants are attacked by various other types of viruses.

Explore further: Virus rounds up enzymes, disarms plant
More information: Patrick Butterbach, Maarten G. Verlaan, Annette Dullemans, Dick Lohuis, Richard G. F. Visser, Yuling Bai, and Richard Kormelink. “Tomato yellow leaf curl virus resistance by Ty-1 involves increased cytosine methylation of viral genomes and is compromised by cucumber mosaic virus infection.” PNAS 2014 ; published ahead of print August 18, 2014, DOI: 10.1073/pnas.1400894111
Journal reference: PLoS Genetics Proceedings of the National Academy of Sciences
Provided by Wageningen University

Read more at: http://phys.org/news/2014-08-virus-dna.html#jCp

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