Hairy tomatoes come with built-in protection

Steve Loewen told participants at the Vegetable Open House at the University of Guelph’s Ridgetown Campus that excessive rainfall has increased the incidence of bacterial disease in Ontario tomato fields.  |  Jeffrey Carter photo

The hairs on a tomato, which are called trichomes, have defensive capabilities for deterring insect threats

Anyone growing tomatoes has likely observed the profusion of tiny hairs. University of Guelph plant breeder Steve Loewen says there are good reasons for their presence.

In science speak, the hairs are known as trichomes, and there are two main types: glandular and non-glandular. Both types appear on the stems and leaves and can be broken down into at least seven subgroups.

Non-glandular hairs are longer and are thought to interfere with the activities of insects trying to feed on tomatoes. Glandular hairs are shorter and also protect against insects.

“Many of the compounds in glandular hairs are toxic to insects and others are sticky — the insects can get stuck in them,” Loewen said.

The hairless mutant tomato, which is found in the wild, actually has hairs but they tend to be distorted, curved or globe-like, Loewen said.

“In some locations in the wild, that’s actually adaptive for the plant. It’s a benefit not to have those (the regular) hairs.”

There are also wooly hairs, which have a silvery or whitish hue and are thought to protect tomatoes growing at high altitudes from the strong sunlight through their reflective quality. At lower altitudes, they may help tomatoes stay cool in hot weather.

Photosynthesis in plants shuts down when temperatures reach extreme levels, Loewen said.

The hairs play a role in Ontario’s processing tomato industry, but it’s the entire genetic package that concerns farmers because it affects yield and fruit quality.

For the Ontario industry, maturity needs to match Ontario’s relatively short growing season. Another important consideration is the ability of the fruit, once ripened, to holds its quality over time.

Loewen works with material into which wild genetics have been incorporated.

He said his chief objectives are to produce lines that are close to being commercially viable and also increase the genetic diversity of processing tomatoes grown in Ontario.

“We don’t release any finished varieties. Our goal is to take on the high risk breeding, working with wild species,” he said.

Lines developed by Loewen and his colleagues are made available to private breeders, who use them to develop commercial lines.

Loewen is also working to develop nutritionally enhanced tomato lines with higher levels of vitamin A, beta carotene, vitamin C and other nutrients.

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