AN ongoing revolution in fruit-tree development is the introduction of heavy-bearing, spur-type apple trees into both commercial and backyard orchards. In many respects it is as significant as the original development of dwarf fruit , sometimes called no-ladder trees.
The trend is particularly important to homeowners, because it means that a very compact tree, taking up relatively little space in the home garden, can produce significant quantities of apples.
These ''compspur'' trees are so named because fruiting spurs (stubby little twigs where blossoms are formed) occur much more frequently on the branches than they do on conventional trees. This heavy-fruiting capacity further reduces the size of a tree, because the bulk of its energy goes into producing fruit each year rather than increasing tree size. In other words, it does just what the backyard orchardist wants.
Some years ago it was noticed that individual branches on some older trees would develop these fruiting spurs far more abundantly than anywhere else on the same tree. No one was quite sure why. But, horticulturists reasoned, if grafting wood were taken from these particular branches, perhaps entire trees capable of such exceptional fruiting would come about.
The theory was tested over many years and found to be correct. Thus the compspur trees came about.
All the more popular varieties are now available in this heavy-fruiting, size-reducing form. Two more recent ones are the Granny Smith and the Arkansas Black, or Arkblack, sometimes known as the Black Twig.
When the British Empire was expanding through the Southern Hemisphere, the colonists took along their English apples. But except in isolated, climatically suitable regions, none did quite as well in these warmer climates as they did back home. Then one day a seedling, a chance cross between who-knows-what species, grew up in an Australian garden to produce apples like no other. They were green, crisp, tart yet sweet, and were good for cooking, drying, and juicing, as well as eating fresh.
No other apple, even back in Europe, had all those qualities rolled into one. Most important, the apple did not mind the long summers and short winters. As the original seedling had grown up on the old Smith homestead, the new apples were referred to by the locals as ''Granny Smith's,'' a name they retain to this day.
They rapidly spread around the English-speaking Southern Hemisphere in the first quarter of this centry and in recent decades crossed the equator because of customer demand. They turned up first in southern France, where French orchardists, proud of their own national varieties, nevertheless recognized a good economic opportunity when they saw one.
More recently they arrived in California, turning that state into something it never thought it could be - an apple-producing region. The most recent estimate lists 6,000 California acres under the green apples. Granny Smith could never have dreamed she would one day do so much for Americans.
While the Granny is an obvious choice for home gardeners in California and other warm regions of the United States, the apple has proved itself in the North as well. Trees have fruited so regularly at the Miller Nurseries here in Canandaigua that the company has included them in its catalog.
Obviously the Granny Smith should not be grown as a commercial venture this far north, but the individual homeowner might well plant a tree or two. Bear in mind that colder Northern temperatures sometimes put a slight red blush on the skin of the otherwise all-green Granny Smith.
Arkblack, another chance seedling, comes from Arkansas, but it is no warm-climate apple. It originated in the mountains of that state, where temperatures are much closer to New England's than they are to those around Little Rock.
The skin of Arkblack is such a dark reddish purple that from just a few feet away it appears black. It has a waxy surface that polishes up to a high luster when rubbed. Put it in a dish with red and yellow apples, and the combination is stunning.
The flesh of Arkblack is a pale cream in color and has a sprightly flavor. Reportedly it makes a great baking apple, is fine for spiced apple slices, and is a natural in pies and sauces.