The Story of Hybrid Onions

by H. A. JONES and A. E. CLARKE

SCIENTISTS have succeeded in crossing suitable inbred lines of onions and obtained excellent results. One hybrid was more than three times heavier than either parent. Other hybrids were outstanding in shape, size, uniformity, and time of maturity. Even more significant : The results showed great possibilities for using hybrid seed for commercial crop production.

Between these encouraging results and the first development of the methods that make possible the production of hybrid seed of all types and in quantity lay a good deal of painstaking, tedious work—work that some of us believed could never succeed.

In the ordinary onion, male and female parts are in the same flower (the perfect flower), and thus each plant is capable of pollinating itself. To get hybrid seed it is therefore necessary to remove the pollen-containing anthers of the female parent, a procedure known as emasculation. Emasculation is not so easily performed with the onion as with corn, whose male and female parts are entirely separate. In corn, emasculation consists merely in removing the tassel. In the onion, the male and female parts are close together, and emasculation is tedious and difficult, because the pollen-bearing anthers must be carefully snipped out with tweezers—a process entirely too expensive for commercial production.

This obstacle, however, has been surmounted. Onion plants are now available whose flowers are not perfect, as they contain no fertile pollen. They are solely female as far as breeding is concerned, and emasculation is unnecessary. In 1925 a plant of this nature was found in the breeding plots at Davis, Calif., in the variety Italian Red. It was given the pedigree number 13-53. It cannot pollinate itself and thus cannot be carried along by seed, but, fortunately, it usually produces large quantities of head sets or bulbils, and these are used to preserve and increase this line.

Two somewhat different methods are now in use to produce hybrid onion seed, but in each case the hybrid seed is produced on naturally female plants that have been crossed with desirable males. These methods are not difficult to understand, but they are different from those used for any other crop. In the first the female line Italian Red 13-53, which is propagated by top sets, is used. Hybrid seed is produced on the female plants when crossed with pollen-bearing plants. In this method only two lines need to be carried along, the female line and a selected male parent.

The second way is slightly more complicated, but has greater potentialities. Female plants have been produced in other varieties of onions and are perpetuated through seed and not vegetatively by bulbils, as is 13-53. Consequently, we can make innumerable combinations in our quest for the best hybrids. Three lines must be carried along instead of two. Just why this is necessary will be shown. We shall tell the advantages and disadvantages of the two methods, and because of the singular part played by the Italian Red 13-53 selection, we believe that a record of its discovery and history is important.

In the early fall of 1924, 63 Italian Red bulbs were selected from a commercial lot and planted in the vegetable-breeding plots of the University of California at Davis. The plants were grown through the winter, and the following spring the flower heads were enclosed in manila paper bags to aid self-pollination and prevent crossing. The bags were tapped several times each day to distribute the pollen inside the bag and to facilitate pollination. On August 8, 1925, the seed heads were harvested. The weather was satisfactory for seed setting, and most of the plants gave a good supply. An especially good plant, Italian Red 13-52, produced 5,866 seeds. On 15 plants, however, no seed was produced. Some of this sterility may have been due to seed-stem rot. One of the seedless plants, the one with the pedigree number 13-53, differed from the other sterile ones in that the seed heads were packed with small sets or bulbils. Its 5 seed stems had 136 sets; the ability to produce head sets saved it from extinction. Its designation, 13-53, should not be forgotten, for it is probably destined to be the most important onion bulb selection ever made.

From 1925 on, 13-53 was propagated vegetatively by use of small head sets. As the bulbils can be held in storage for only a few weeks, they are usually planted in the nursery soon after harvest. They are then transplanted to the field in late fall or early winter and over-wintered as growing plants. When they are planted on productive soil, the foliage grows luxuriantly, and the large, spindle-shaped bulbs usually Mature in late June or July. Because of their poor keeping quality, these large bulbs are again planted back into the field in September and overwintered in a mild climate as growing plants.

How two onions are crossed to get the California Hybrid Red No. 1. It combines the early maturity of Lord Howe Island and delayed bolting habit of 13-53.

Since its discovery, 13-53 has been grown under a wide range of climatic conditions. During this time, seed has never been produced when the flower heads were properly protected from pollen by bagging or by isolation. When the flowers are well pollinated, however, they give a heavy set of seed. Even when loaded with seed, the flower heads continue to produce bulbils almost as though no seed had been produced.