Heirloom strains add vigor to new crossbreeds

Not many regions of the world came more poorly endowed with food-producing plants than the United States and the Canadian provinces to the north. But something particularly good happened during the settling of North America that enabled it to contribute most handsomely to world agriculture.

When farmers of the Old World saw a brighter future in the New World, they brought with them the most productive vegetables and grains they had known back home.

And while the farmer from England and his newly arrived neighbor from Germany struggled for a year or two before they could communicate readily, their respective fields of grain, as well as their apple and peach orchards, knew instant compatability.

Bees and other insects, aided by the wind, cross-pollinated the English and German varieties, and presumably the Greek, Russian, Polish, and countless other strains. Even English and Scottish strains, geographically close for so many centuries, met up, you might say, for the first time on this side of the Atlantic.

The net result was a sudden upsurge of crossbreeds, many of them superior to the parental stock.

With such a wide selection from all of Europe, as well as Asia and the Middle East, even those varieties that did not necessarily cross easily in nature circulated readily among the pioneer farmers and gardeners on an ''I'll give you some of my peas if you'll let me have some of your great beans'' basis. This way , then, the US became a rich depository for many of the best food-producing strains in the world.

It is these old strains, sometimes referred to as heirlooms, that are currently dying out at an alarming rate. But a grass-roots organization of home gardeners is emerging, dedicated to saving many of these grand old varieties both for their current productive capacity and for what they may have to offer plant-breeding programs in the future.

Breeders frequently reach back to older varieties to infuse vigor into new ones or to add drought tolerance or any of a number of desirable qualities.

Back in 1970, blight wiped out 15 percent of the US corn crop. At the time most commercial varieties of corn were based on a dangerously narrow genetic base, vulnerable to the blight. But, by taking an older variety, breeders were able to infuse blight resistance into the seed crop being grown that year. As a result the problem was overcome in a single season.

While the whole rescue effort dramatically illustrated the skill of the plant breeders, it also pointed up the importance of maintaining the varietal diversity of the past.

When a variety becomes extinct, whatever contribution it might have made to the future is gone for good. Unless some remaining specimens are found in some remote garden, no one will ever again taste the once popular Mr. Topp tomato. It was said to be pleasant tasting, but it had another particularly important quality: It was unusually tolerant of the cold and could survive frosts that wiped out other varieties. Breeders could do a lot with those cold-resistant genes today.

Meanwhile, if you wish to preserve one or more old-time varieties, the Seed Savers Exchange (203 Rural Avenue, Decorah, Iowa 52101) has some recommendations:

Best specimens. Among the plants you wish to perpetuate, choose two or three of the best specimens from which to take seed. Look for vigorous growth, productivity, taste, and any other desirable property you may wish the next generation to have. Feed these plants and keep them well watered unless drought tolerance is a trait you are looking for.

Pollination. To prevent unwanted crossings (carrots will cross with wild Queen Anne's lace), keep similar varieties at least 200 feet apart and grow a high barrier crop such as corn between them. Better still, isolate the chosen plants in a muslin or screen-covered cage. A little decaying meat will help you trap the flies you will need to pollinate the caged flowers. Large flowering plants can be hand-pollinated.

Maturity. Seeds are actually plants in miniature surrounded by a food supply. If the seeds are harvested before they are ripe, they will contain all the plant parts but have too little food to germinate properly. Remember, while tomato seed is mature the moment the fruit is ready to eat, corn must be allowed to develop beyond its peak eating condition.

Drying/storing. Two factors - dryness and cool temperatures - promote seed vitality in storage, which is why 800-year-old corn seed found in a Utah cave was still capable of germinating a few years ago.

Start by drying seeds in the sun. In the more arid Western part of the country, that will probably be all that is necessary. In the more humid East, further drying will greatly increase storage life. A few days in a room heated by a wood or coal stove will dry out the air and the seeds.

Or suspend an electric light bulb above the seeds for a few days. Never try to dry seeds in an oven as temperatures over 100 degrees F. can quickly kill the seeds, and few ovens are capable of maintaining so low a temperature.