Temperate Fruit Crops in Warm Climates at page 178:
A general objective in most breeding programs is higher sugar content
See Survey of Food and Nutrition Research in the United States, which lists a publication titled:
Fruit breeding. Improvement in color, flavor, sugar content, and yield of apricots, plums, peaches, nectarines, sweet cherries, pears, and apples.
Other relevant examples are:
From Proceedings of the 41st Convention of Southern Agricultural Workers:
The purposes of the breeding program in Louisiana are as follows: 1. To breed more uniform shaped table varieties having a higher sugar and carotene content, keeping in mind the ideal type for table as well as for canning.
From Report on the Work and Expenditures of the Agricultural Experiment Stations:
A promising seedling prune has been developed at the Oregon station, bearing a fruit with a higher sugar content than any variety tested
From the 41st Annual Report of the Texas Agricultural Experiment Station:
Breeding of the blackberry will be for the purpose of selecting a fruit of high sugar content
The Relation of Certain Biological Principles to Plant Breeding, page 46:
Previous to the time of Louis Vilmorin, about 1850, there had been some few selections of mother beets for higher sugar content by placing the roots in solutions of different density and selecting those having the highest specific gravity.
Maize breeding and genetics has a section:
Breeding Sweet Corn with Higher Sugar Content
There is also a New York Times article Breeding the Nutrition Out of Our Food:
EUROPEAN settlers were content with this colorful corn until the summer of 1779 when they found something more delectable — a yellow variety with sweeter and more tender kernels. This unusual variety came to light that year after George Washington ordered a scorched-earth campaign against Iroquois tribes. While the militia was destroying the food caches of the Iroquois and burning their crops, soldiers came across a field of extra-sweet yellow corn. According to one account, a lieutenant named Richard Bagnal took home some seeds to share with others. Our old-fashioned sweet corn is a direct descendant of these spoils of war.
Up until this time, nature had been the primary change agent in remaking corn. Farmers began to play a more active role in the 19th century. In 1836, Noyes Darling, a onetime mayor of New Haven, and a gentleman farmer, was the first to use scientific methods to breed a new variety of corn. His goal was to create a sweet, all-white variety that was “fit for boiling” by mid-July.
He succeeded, noting with pride that he had rid sweet corn of “the disadvantage of being yellow.”
The disadvantage of being yellow, we now know, had been an advantage to human health. Corn with deep yellow kernels, including the yellow corn available in our grocery stores, has nearly 60 times more beta-carotene than white corn, valuable because it turns to Vitamin A in the body, which helps vision and the immune system.
SUPERSWEET corn, which now outsells all other kinds of corn, was derived from spontaneous mutations that were selected for their high sugar content. In 1959, a geneticist named John Laughnan was studying a handful of mutant kernels and popped a few into his mouth. He was startled by their intense sweetness. Lab tests showed that they were up to 10 times sweeter than ordinary sweet corn.
Mr. Laughnan was not a plant breeder, but he realized at once that this mutant corn would revolutionize the sweet corn industry. He became an entrepreneur overnight and spent years developing commercial varieties of supersweet corn. His first hybrids began to be sold in 1961.
Within one generation, the new extra sugary varieties eclipsed old-fashioned sweet corn in the marketplace. Build a sweeter fruit or vegetable — by any means — and we will come. Today, most of the fresh corn in our supermarkets is extra-sweet. The kernels are either white, pale yellow, or a combination of the two. The sweetest varieties approach 40 percent sugar, bringing new meaning to the words “candy corn.” Only a handful of farmers in the United States specialize in multicolored Indian corn, and it is generally sold for seasonal decorations, not food.
We’ve reduced the nutrients and increased the sugar and starch content of hundreds of other fruits and vegetables.