New varieties defeat disease

January 22nd, 2016 | Plant Talk with Graham Rice | 0 Comments

Disease resistant Nicotiana 'Whisper'What do you do when a deadly new disease strikes down your favourite plant? It’s happened a couple of times recently but in neither case has the answer been: get out the sprayer.

First it was tobacco plants (Nicotiana). Blue mould wiped out the Royal Horticultural Society’s trials of Nicotiana in 1997, 1998 and again in 2001- after which the RHS, quite rightly, gave up. And so did everyone else. Plant breeders who specialised in nicotianas also had their trials wiped out and, in fact, gardeners were in the least bad position, as you might say. Clumps of half a dozen plants in individual gardens were less likely to be hit than thousands of plants all grown together. But they still suffered.

It was the popular varieties of Nicotiana alata that were so badly hit. Varieties like ‘Sensation’, ‘Lime Green’, ‘Nicki’, ‘Domino’, ‘Merlin’, ‘Avalon’ all suffered – it was far too much of a gamble to grow them.

So plant breeders turned to species which had rarely been grown – and which proved to be resistant. It took a while, but the most successful result is ‘Whisper’. Developed in Norfolk using mould-resistant species, the mixture comes in a lovely range of dark and pale pink shades.

Then the same thing happened with busy lizzies (Impatiens). All our Impatiens 'Divine Islander Mix'favourites including ‘Accent’ and ‘Super Elfin’ were suddenly struck down by a virulent mildew and the seed companies and garden centres cut back on the varieties they offered or stopped offering them altogether. It’s now impossible to recommend them.

But plant breeders were already developing a different type of Impatiens, New Guinea impatiens, which is tolerant of the disease. The flowers of the early varieties were larger than those of the old favourites but the plants needed hot summers. Fortunately, in more recently introduced varieties, this demand for summer heat has been reduced and the ‘Divine Islander’ mixture and the new Big Bounce Series are much more adaptable. So, as with clubroot resistant brassicas and virus and blight resistant tomatoes – the plant breeders have come to our rescue.

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Is one of our best known gardening writers. A graduate of the Royal Botanic Gardens, Kew, Graham was previously Gardening Correspondent of The Observer.
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