CROP FLOP; gardening Do disease-resistant plants really work? By Hannah Stephenson.

VEGETABLE gardeners whose crops have in the past been decimated by diseases are always on the look-out for varieties labelled "disease-resistant".

But do they actually work?

Gardening Which? tests proved hugely disappointing. The Consumers' Association magazine trialled 14 varieties - five flowers and nine vegetables.

The verdict, in the June issue, concludes: "We were hoping that at least some of the so-called resistant varieties would be sufficiently less affected so that we could recommend them. Alas this is not the case."

While breeders are constantly working hard to identify the genes which make plants resistant, it's difficult because disease can mutate almost as quickly as the production of new varieties.

Researchers tested the most common diseases including potato blight (which also affects tomatoes), clubroot, rust, powdery and downy mildew. Most plants were raised from seed, and each was grown alongside a similar but non-resistant variety.

The newest blight-resistant tomato variety, Fantasio, was grown alongside the nonresistant Ailsa Craig and while the latter was worst affected, with up to half the developing fruit damaged.

Cabbages and swedes were tested for clubroot, which causes the roots to swell and burst, reducing crop yield.

Tests found that the resistant swede Marian showed severe symptoms, while the resistant cabbage Kilaxy (Suttons) was less affected than its nonresistant counterpart Marner Large White.

Two flower varieties were tested for rust - which weakens plants as they show symptoms of powdery orange, yellow, brown or black spots on the leaves - the antirrhinum Rust Resistant Mixed and nonresistant Liberty, and the hollyhocks Antwerp, which claims resistance, and Pastorale, which doesn't.

Tests found there was no difference in the rate of infection for the hollyhocks, while the resistant antirrhinum actually suffered more.

Tests on phlox Blue Paradise, which is said to be resistant to mildew, and the non-resistant phlox Fujiyama, showed that both were badly affected by mildew, while there was also no difference in the result of tests for downy mildew on the so-called resistant butterhead lettuce Milan and the nonresistant All the Year Round.

Both became equally infected. The best bet is to stick to your favourite varieties and try alternative ways to prevent disease. Keep tomatoes away from potato crops and ensure foliage stays dry by watering the soil only.

If you have clubroot-infested soil, lime it regularly to keep the soil above pH7, as clubroot prefers acid soil, improve drainage and start brassicas off in pots of compost, planting out when well established.

For flowers suffering from rust, remove affected leaves, don't use a lot of nitrogen fertiliser, which produces lush soft growth, and consider crop rotation for your veg.

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