14 April 2000

ELISA test may

offer early leaf blotch warning

By Andrew Blake

WHATEVER the true cause of barley leaf blotch, ELISA testing might help predict it before visible symptoms appear, CSC work suggests.

"We first saw leaf blotch in 1993 and it seems to be more of a problem the further north you go," says the firms John Hughes. "And it doesnt just affect spring varieties. Vertige was really knobbled by it last year."

Mid-June ELISA testing last year on several varieties highlighted a range of results which appeared to mirror eventual blotch levels.

In the north Chariot, the worst hit, registered a reading of 27. In Aberdeen the figure was 15, but was up to 24 a week later when the dull blotch symptoms first showed, he says. By contrast the less affected Optic and Decanter recorded readings of 9 and 6 respectively early on.

By June 21 Vertige was registering 110. "Thats the sort of level we ended up with in some spring varieties," says Mr Hughes.

"It shows we are picking something up, perhaps some resting spore stages, although it is not too specific.

"Leaf blotch is definitely to do with disease. The question is: What allows it to take hold?

"We can get quite high ELISA readings on Prisma, but that doesnt seem to have a detrimental effect, so there is varietal susceptibility."

Triazole fungicides offer some protection, but only up to flag leaf emergence. "The leaf blotch then seems to get the better of them."

Strobilurins do not provide 100% control but seem to do a better job when sprayed early. "Thats possibly because they stop the fungus actually getting into the leaves," Mr Hughes speculates.

Whatever the infection mechanism only Prisma in Black Isle blotch-affected trials last year failed to show a return from using strobilurins instead of a Fortress/Sanction (quinoxyfen/flusilazole) approach.

Pollen acting as an energy source for the fungus may be involved, he believes. Prisma is a relatively close-flowering type. "Is it a co-incidence that the more open-flowering varieties producing the most pollen are the most affected?" &#42

BARLEY LEAF BLOTCH

&#8226 Worsens towards north.

&#8226 Early ELISA detection.

&#8226 Varietal susceptibility.

&#8226 Strobs generally useful.

New test looks set to provide early warning of barley leaf blotch, says CSCs John Hughes.