How Hybrid Seeds Differ From Heirloom Varieties
WEYMOUTH, MASS. — SOMETIME in the 1870s, American plant breeder Eugene Davis grew his favorite American and favorite English lettuces side by side in a special greenhouse erected for that purpose. He did this in the expectation that they would cross-pollinate rather well and in the hope that one or two of the resultant progeny would exhibit qualities superior to both parents.
He was right on both counts, and after several years of selectively breeding from subsequent generations of that original cross, he came up with a winner - a variety he named Grand Rapids. In the more than 100 years since that breeding effort, Grand Rapids lettuce has grown so consistently well that today it is still available commercially.
Mr. Davis's approach to plant breeding, typical of his era, is no longer commonplace today. The lettuce produced by the Michigan breeder resulted in what is called an open-pollinated variety. In other words, seeds saved from the plant would produce offspring with markedly similar traits, which meant any seed producer could quickly capitalize on the breeder's years of hard work by growing as much of the superior seed as they wished.
Today, capitalizing on another's hard work is not so easy, because seed companies footing the bill for a new variety insist that their invariably heavy investment be better protected than in the past. So they produce what is termed F1 hybrid seeds that produce plants that cannot reproduce themselves.
HOW is this done? Well, if Davis were to breed his Grand Rapids lettuce as an F1 hybrid today, he would begin by growing the same two parent varieties but keep them in separate greenhouses. Over several seasons, he would make careful selections from the two lines separately until he had the qualities in each variety that he wanted to combine in a new single variety. Only then would the cross would be made.
The result of crossing two very inbred lines is offspring with remarkable hybrid vigor. But the special traits that make the hybrid plants desirable cannot be reproduced in the next generation.
In somewhat oversimplified terms, then, the F1 hybrid is the result of years of careful selection preceding the crossing of the two parent lines; in the open-pollinated varieties, the several generations of careful selection follow the initial cross-breeding, which means that the valued qualities are stabilized in the variety and can be passed on from generation to generation.