12 July 2002

Mystery leaf chlorosis hits wheat variety Xi19

By Andrew Swallow

CONCERNS are mounting that yields of some crops of potential milling wheat variety Xi19 could be hard hit by a mystery chlorosis of the leaves.

Despite robust fungicide programmes large lesions that look like septoria, but lack the picnidia, have appeared throughout the canopy, prompting one agronomist to predict a 50-60% yield loss.

Symptoms have been seen from Yorks southwards. Breeder Advanta is urging growers to contact it in the hope that a common cause can be identified.

Technical and marketing manager, Paul Hickman, says pollen scorch, drought stress, or problems caused by fertiliser and crop protection products could all be factors.

"The likelihood is that it is a physiological stress effect. It appears some combination of circumstances has weakened the plant and then it has been compromised by a fungus."

NIAB pathologists have identified the fungus Didymella exiatis on an initial sample. But Mr Hickman stresses that it was only one leaf from one crop.

ADAS agronomist Andrew Wilkins has clients with affected Xi19 crops on light soils in both Staffs and Shropshire. "Early symptoms were a yellowing of the leaf on the flatter areas, and in the axils."

In the worst case those initial symptoms have spread, leaving just 25% of the flag leaf green and the rest of the canopy gone. "It is going to have quite a big yield impact, 50-60% yield loss may be the order of the day."

But Mr Hickman says it is too early to predict likely yield loss, if any, and cannot say whether growers should expect compensation. "I do not want to speculate. It seems an odd combination of events has caused this. We have not seen anything like it in five years of trials."

ARCs western regional manager, Richard Overthrow, says symptoms seem more common in the south and west. Xi19 plots, both treated and untreated, have been hit in Warks, Glos and Hants trials.

"It has taken out a lot of leaf area, so we expect quite a lot of yield loss."

Something genetic may be at the heart of the problem, he says. Two other Advanta varieties, Warlock 24 and Scorpion 25, are also showing similar symptoms. Like Xi19 they both have Cadenza in their parentage.

Reports of problems from growers are more common on light land than heavy, he adds. Eastern region colleague Stuart Knight echoes that view.

Xi19 on sandy clay loam over gravel in Essex looks to have a severe problem, says Mr Knight, while on heavier ground at Biggleswade, in Beds, there are only slight symptoms.

"At least some of the symptoms are very similar to pollen scorch, but not all. So it is probably only part of the story. We await the views of the breeder." &#42

Xi19 Update

Updates on findings will be posted on the physiology section of the variety web-site www.Xi19.com. Concerned growers can e-mail Advanta from the web-site, or phone on 01485-518501, or fax: 01485-518741. "Please do contact us with a full cropping history," says Mr Hickman. "We are trying to put the links together."

Xi19 CHLOROTIC CONCERNS

&#8226 Unexplained yellowing of leaves.

&#8226 Multiple causes under investigation.

&#8226 Up to 80% green leaf area lost.

&#8226 Yield impact uncertain.