The Benefits and Costs of Disease Resistance in Wheat

| 3/14/2014 8:06:00 AM

Tags: grain, growing wheat, wheat breeding, Stan Cox, Kansas,

wheat rustIn the April-May and February-March issues of MOTHER EARTH NEWS, I discuss some aspects of growing your own wheat: variety selection, growing methods, and processing of the harvest. One of the more important considerations in deciding which kind of seed to plant is the variation among wheat varieties in their reaction to fungi, bacteria, and viruses that can cause disease.

Wheat is plagued by a wider assortment of diseases than are most other grain crops. (North Dakota State University provides a good photographic compendium of wheat diseases.) The particular array of microbial threats varies from region to region and year to year, but few places escape completely. And when severe, diseases can wreck both the yield and the quality of harvested grain. Over the past century, wheat breeders have put at least as much effort into selecting for naturally-occurring genetic resistance to disease (no GMOs needed!) as they have into breeding for higher yield. In general, recently-developed varieties tend to have better resistance than do older ones; however, that is not always true, and almost every variety has one or more Achilles heels.

The risk-averse should simply avoid varieties that are especially susceptible to diseases that often strike wheat in their area. Many wheat growers plant a blend of two or more varieties. The logic of blending is that a mixture is more well-buffered against weather, diseases, and insects: when one variety has a bad year, others may take up the slack. But varieties included in the blend should be either all winter or all spring types with similar heights and harvest dates.

Guides to varieties, with disease-resistance ratings, are available for Eastern soft wheats, Great Plains hard winter wheats, and Northern hard red spring wheats, and there's also a guide for growing variety blends.

For wheat growers, it's a truism: Sow varieties that are resistant to prevalent diseases. But what if the wheat plant has to give up something for its resistance, so that it is less productive or its grain makes poorer bread? Would the resistance then be worth it?

Those are not questions that can be answered without controlled experiments. Simple observation can be deceptive. Close your eyes and think of any two wheat varieties; they will very likely differ in their geographical adaptation, yield potential, and reaction to the huge range diseases that infect wheat. If, for example, you happen to compare a specific rust-resistant variety with a susceptible variety, the resistant one might yield less or make poorer-quality bread than the susceptible one in a year without rust. (Depending on which ones you've picked, it could also yield more or make better bread.) However, that does not mean that resistance causes lower yield or quality. The two varieties differ not only in that rust gene, but also carry contrasting genes throughout their genomes. Any of those genetic differences could contribute to a difference in performance.

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