Even though our gardens are more than three thousand miles apart, GrowVeg founder Jeremy Dore and I experienced similar tomato miracles in our gardens last year: the plants did not die. Eventually they did, of course, but with the help of special genes, the plants did not melt down with late blight following periods of rainy weather. We both grew blight-resistant tomato varieties for the first time, and now we can't wait to try more of these naturally healthy tomatoes.
First let's clarify what we mean by "blight." Tomatoes in a wide range of climates are bothered by early blight (Alternaria solani), a fungal disease that causes dark spots to form on the lowest leaves. Early blight needs damp leaf surfaces to prosper, so the shaded leaves low down on the plant, which dry slowly, wither from early blight while lovely new growth continues higher up, where sunshine and wind keep the leaves comparatively dry. Evidence of this extremely common disease are plants with withered foliage to about 18 inches (46 cm) from the ground, with healthy green growth higher up. Early blight weakens tomato plants but does not kill them.
Late blight does kill tomato plants, and once the killing starts there is no stopping it. Caused by a fungus-like oospore, late blight (Phytophthera infestans) also devastates potatoes. Unlike early blight, late blight on tomatoes develops later in the summer, and always following a period of prolonged rain. Moisture and plenty of it is required to bring late blight to life, but problems have become much more widespread in recent years, especially in the north and eastern US, where late blight of tomato has gone from being an occasional problem to a constant concern.
Enter new varieties imbued with two or more genes that give them excellent resistance to late blight, and some resistance to early blight, too. And not to worry, these genes were manipulated using traditional breeding techniques, mostly under the direction of Dr. Randy Gardner, Professor Emeritus at North Carolina State University, who has been breeding better tomatoes for more than 30 years. Gardner and his team began making progress with blight resistance in the late 1980s, but their great gift to the gardening world came in 2010, when they released an ensemble of breeding lines with multigenic resistance to both blights to anyone who wanted to work with them.
The variety I grew, 'Mountain Magic', came directly from Gardner's program, but several more blight- resistant tomato varieties show the finishing touches of other breeders – including home gardeners who work with heirlooms. In 2012, when researchers in New York evaluated late blight tolerance in 35 tomato varieties, the winners were an interesting mix of hybrids ('Defiant', 'Plum Regal', 'Mountain Magic 'and 'Mountain Merit') and heirlooms 'Lemon Drop', 'Matt's Wild Cherry', and 'Mr. Stripey' (also called Tigerella). More recently, super-resistant 'Iron Lady' was added to the list, along with 'Jasper', a tasty red cherry. See the alphabetised list below of these blight-resistant tomato varieties.
The Troubled Trans-Atlantic Crossing
While US gardeners have plenty of choices among disease-resistant tomatoes, the only up-to-date variety available in the UK appears to be 'Jasper', which has earned an RHS Award of Merit. The variety Jeremy grew with such excellent results was 'Fantasio', which likely has single-gene resistance to late blight. An older hybrid, 'Ferline', fits into the same category; it will hold up under light disease pressure but will succumb when things get really bad. US-bred 'Legend' is also recommended to UK gardeners for its disease resistance, but it never emerged as a winner in the US, probably due to its single-gene resistance.
Until European seed companies start selling the vastly improved new American varieties, the most economical option for gardeners in the UK and other countries who want to try them is to have a friend buy seeds in the US (from Jung or Johnny's, for example), and send them on. If you were travelling from outside the EU, you would be allowed to bring back up to five packets of commercially-packaged seeds, and the same import policy appears to apply to mailed seeds. One US seed company, Tomato Growers Supply Company, will ship international orders for a flat special handling fee of $12 USD.
Blight-Resistant Tomato Varieties for 2014
- Defiant – Determinate (bush) plants produce round, medium size red fruits, rated at 70 days to maturity.
- Iron Lady – Determinate (bush) plants produce round, medium size red fruits, rated at 75 days to maturity.
- Jasper – Tall indeterminate (cordon) plants bear trusses of red cherry tomatoes starting 60 days after planting. An All America Selections winner and RHS Award of Merit.
- Lemon Drop – Indeterminate (cordon) plants bear hundreds of small yellow-green tomatoes in 80 to 90 days. Open-pollinated heirloom variety, a sport of 'Snow White' cherry.
- Matt's Wild Cherry – Sprawling indeterminate (cordon) plants bear scads of tiny red cherry tomatoes starting 55 to 60 days after planting. Open-pollinated heirloom from Mexico.
- Mountain Magic – Vigorous indeterminate (cordon) large red cherry tomatoes, rated at 75 days to maturity.
- Mountain Merit – Determinate plants produce large red round fruits about 75 days after planting. An All-America Selection winner.
- Mr. Stripey – Indeterminate (cordon) plants produce medium size round fruits marbled with red and yellow in about 80 days. Open pollinated heirloom.
- Plum Regal – Determinate plants produce red plum tomatoes weighing 3 to 4 ounces each, rated at 80 days to maturity.
By Barbara Pleasant