4 December 1998

Barley virus strain needs watching

A NEW strain of Barley Mosaic Virus which attacks varieties known to be resistant to Barley Yellow Mosaic Virus and Barley Mild Mosaic Virus has now been confirmed at 30 different locations across the UK.

Although it shows similar symptoms to the other two forms of the virus, Race 2 is causing more concern because there are no varieties currently on the UK market which are resistant to it.

"That means that growers with soil found to be infected with Race 2 may have to give up growing winter barley in time," says Dr Mike Carver of ARC. "It has been shown to reduce the yields of an otherwise resistant variety by 37%."

Race 2 is a breakdown race believed to have come from Barley Yellow Mosaic Virus, he explains. "It is probably been present in the soil for some time, but has been masked by the two dominant strains. In the absence of resistance, it could spread rapidly."

Test samples

He urges farmers with suspect fields to take samples for testing in early February. "It is important to know which race you have got. Providing it is not Race 2, then varieties can be chosen accordingly. Some varieties grow better in the presence of one race than the other."

Testing for Race 2 has been done at IACR-Rothamsted, where trials are being run in conjunction with ARC on the spread of the new strain and its effect on yield.

Dr Carver confirms that there is nothing that can be done agronomically to overcome infection. "ARC work has shown that changes to nitrogen rates and timings, seed rates and crop rotations make no difference. Delayed drilling does reduce the severity of mosaic virus infection but it also reduces yield.

He adds that the mosaic virus is soil-borne in a fungus. "That means that sharing cultivation machinery will spread it. Anything that transfers soil from one field to another is risky."

Dr Carver admits that all three races of the virus can exist within the same field. "Weve seen large patches of Race 2 infections develop very quickly. Growers need a broader base of resistant material from plant breeders if they are going to overcome it." &#42