If you have ever traveled by car through the Corn Belt section of our great Midwest, I’m sure you’ve seen signs reading something like “DeKalb Hybrid No. 873,” or “Pfister Hybrid No. 473,” standing adjacent to large fields of the world’s finest corn.
Perhaps you’ve wondered at the time why nearly all of the corn being grown today is F1 hybrid corn—and why, within the last few years, new varieties of F1 hybrid petunias, begonias, snapdragons, and many vegetables are appearing in various seed catalogs.
The Start Of F1 Hybrids
You needn’t look far for the answer. These new F1 hybrids are vastly superior to older varieties in the vigor of growth, disease resistance, and uniformity of plant habit.
F1 hybrid flowers produce a far greater number of blooms over a longer period, while vegetables yield more heavily. “All very fine,” you say, “but just what is an F1 hybrid that should be so much better?”
Before we dig into the answers to these questions, let’s observe what nature has been doing along this line for centuries—long before man realized that such things as sex and inheritance even existed in plants.
If every plant remained exactly as it was created, what chance of survival would it have if a major climate change altered its growing conditions?
One of the devices that nature has contrived to meet situations of this sort is the provision for cross-pollination between different kinds of plants (within broad family groups) by bees, moths, insects, and other means.
The wide assortment of crosses or “hybrids” thus produced gives rise to new forms of plants, a few of which, in later generations, will prove to be more adaptable to the new set of growing conditions by the process of “survival of the fittest.”
This rather simplified explanation of one of nature’s marvelous provisions for the perpetuation of plant life is cited here to show the fundamental workings of the process that man stumbled onto, probably sometime in the early part of the eighteenth century.
Before this time, our early ancestors were likely too busy securing the bare necessities of life to pay much attention to plants, whose only value was that of beauty.
When early man first had time to devote to flowers, he probably transplanted entire clumps of wildflowers to his dooryard.
The Practice Of Plant Selection
It seems only natural that he should have chosen the best and, in doing so, practiced the first plant selection in ornamentals.
As time passed, flowers played an increasingly important part in his everyday life, as evidenced by their presence in remnants of early art.
While early records of attempts to breed flowering plants are very meager, considerable work along this line had undoubtedly been done by the beginning of the 18th century. Apparently, the first authentic record of hybridizing flowers, however, appeared in 1717.
This involved a cross that Thomas Fairchild had made between a carnation and a sweet William. and occurred when Camerarius demonstrated the existence of sex in plants after this fact had become generally accepted.
Many amateurs probably became engaged in some sort of breeding work with flowers. The development of new varieties indicates the wide interest in this type of work during the nineteenth century.
While the work of skilled plant breeders, thoroughly trained in genetics (the science of heredity based upon the laws discovered by Gregor Mendel) is responsible for today’s fine F1 hybrids, many improved types of flowers are being produced by amateur breeders. Most of whom work on a very small scale in a backyard garden.
The Discovery of Sex In Plants
Now that we have established a smattering of the basic assumptions and facts concerning the discovery of sex in plants, let us examine one of the corn plants we spoke about in our opening paragraph.
The ears of corn contain the kernels or, more properly known, the ovules, the female reproductive cells. To each ovule is attached one “silk” or style, ending in the stigma, which is the tip of the silk exposed to the air.
The corn plant terminates its growth in the tassel. Here, the anthers are borne, which produce the dustlike pollen, or male reproductive cells. In the case of corn, we see that the two sexes are borne on different parts of the plant.
When the pollen is ripe and fertile, the wind carries it in great clouds to the stigmas on the end of each silk, where it germinates and grows down the silk to the ovule or kernel. fertilizing it and producing the seed because corn is wind-pollinated.
It must be planted in blocks rather than in single rows since the latter method does not permit satisfactory pollination and results in many partly filled ears because of the failure of many silks to be dusted with pollen.
Some other vegetables produce separate male and female flowers, as do some ornamentals.
The ordinary fibrous-rooted begonia, common in florists’ shops and greenhouses, is an example of this type. However, most ornamentals carry both sexes in the same flower.
This is true of petunias, and since petunias are probably the most popular garden annual being grown today, and because any list of “who’s who” in petunias contains some very fine F1 hybrid varieties, we will discuss this versatile plant in some detail.
Wide Assortments Of Colors
A glance at nearly any flower seed catalog will reveal the wide assortment of colors and types of petunias with which the gardener can grace his or her flower beds or window boxes today.
Ranging in size from profuse blooming, single-flowered types, an inch and a half across, through the larger ruffled and fringed grandifloras, up to the huge 6-inch CALIFORNIA GIANTS, and the strikingly beautiful fully double varieties.
They embrace all colors except yellow. This has not always been so. However, only recently has a true scarlet red been on the market.
The self-pollinated variety FIRE CHIEF was the first true red. It is being rapidly replaced by the superior F1 hybrid Comanche—the same color but superior in growth and quantity of flowers.
Where Popular Petunias Come From
But we’re getting a hit ahead of our story. Where did the first petunias come from, and when did they become popular?
The ancestors of our modern varieties are reported to have arisen out of a cross between the wild petunia species Petunia axillaris and P. violacea, both of which are natives of Argentina.
Even so, the first petunia varieties were rather dull in color—mostly in pale lavender and magenta shades. And certainly, they weren’t very popular in the early part of the present century.
It remained for Theodosia Sheppard, a hobbyist in her garden in Southern California, to develop the first of the large, colorful grandifloras, CALIFORNIA GIANTS, and doubles, comprised the forebears of today’s wonderful varieties.
Since most of the world’s commercial flower seed production before the first World War was centralized in Europe and much of it in Germany, it was only natural that skilled German plant breeders originated most, if not all, of the varieties which started the petunia well along the road to popularity in the years immediately preceding and after the first war.
A few of these varieties, notably ADMIRAL, LACE VEIL, ROSE OF HEAVEN, and CELESTIAL ROSE are still rather widely grown. The last-named variety was introduced to the American trade in 1934 by George J. Ball and became the largest-selling petunia of all time.
Self-Pollinated Kinds That Produce Both Sexes
F1 hybrids were still a thing of the future, and all of the varieties we’ve been discussing were “inbred” or self-pollinated kinds. Recalling that petunias produce both sexes in the same flower, this was a comparatively simple matter.
Suppose you carefully tear apart a newly opened petunia flower. In that case, you can observe the five male stamens with their anthers of white or bluish pollen surrounding the female pistil surmounted by its sticky stigma and the ovary containing the tiny ovules at its base.
If the pollen of this flower is applied to its stigma, and seeds are thus produced, the process is referred to as “selfing” or inbreeding.
If the pollen is applied to the stigma of an entirely different petunia variety, the resultant seed is called F1 hybrid seed, and the plants grown from this seed are F1 hybrid plants.
The term “F1” simply means “first filial generation,” or the first children of the parent generation.
In either “selfing” or cross-pollinating, the plant breeder must be sure that only the wanted pollen reaches the stigma.
In both cases, the plant is usually protected by a cage covered with finely screened material, such as cheesecloth or Saran screening; or the individual flowers to be used are covered with a suitable small paper bag or glassine envelope before the bud has opened until after fertilization has taken place.
This way, stray bees, and insects are kept from bringing unwanted pollen to the flowers. Since it is important to see that the right pollen reaches the stigma, this is usually done with a small watercolor brush or with the fingers.
Cross-Pollinating F1 Hybrids
In cross-pollinating to produce F1 hybrids, one additional step is necessary.
The larger petunia flower buds must be carefully torn open and the anthers removed before they have shed their pollen, which might result in self-pollination. After a lapse of two or three days, pollen is applied from another variety.
The pods usually ripen in three to six weeks, depending on the prevailing weather. In commercial production F1, the hybrid petunia seed is normally produced in a screened greenhouse, or other measures are taken to prevent contamination by unwanted pollen carried by bees or insects.
After examining the techniques used in producing petunia seeds, let’s return to the earlier mentioned self-pollinated varieties like CELESTIAL ROSE.
This variety and others to follow became the parents of the first F1 hybrid petunias to appear on the market.
One of the best-known of the more recent self-pollinated varieties was the All-America winner, FIRE CHIEF.
It gained wide prominence almost overnight because it represented an entirely new color in petunias—a flashy scarlet red. But within three years, it has been superseded by the F1 hybrid COMANCHE, which uses FIRE CHIEF as a parent.
Superior Comanche
What is the secret something that makes COMANCHE so much better than its parent, FIRE CHIEF? Plant breeding science still doesn’t have the full answer.
We know that COMANCHE is superior to FIRE CHIEF in its greater vigor, faster growth rate, and profusion of blooms, but what makes these facts?
We only know that when two petunias have been closely inbred for several generations and then crossed with each other, a remarkable stimulation takes place, which we call hybrid vigor or “heterosis.” Someday we hope to know more about it.
In addition to COMANCHE, other popular F1 hybrids include CRUSADER, BALLERINA, TANGO, and SILVER MEDAL.
New ones for 1955 are the following:
- APACHE, deep rose
- Sioux, deep salmon
- PALEFACE, pure white
- PRIMA DONNA, extra large rose pink
And last, but by no means least, the huge, fluffy doubles are all F1 hybrids. They’re produced by crossing single-flowered varieties with pollen from a special type of full-petaled double.
44659 by Philip Jones