Problems and Rewards in improving Seeds

JOHN H. MARTIN AND S. H. YARNELL.

THE NUMBER of acres that are planted to a variety of a crop may depend on the availability and cost of its seed.

The point is important and as simple as 1-2-3: Some farmers buy low-priced seed although they know it is inferior. The cheap seed often makes a poor crop. Seed can be produced at lowest cost when a heavy-yielding variety is planted.

Here are some examples:

Soybeans largely replaced cowpeas for hay and green manure purposes because soybeans give higher yields and the seed costs less.

Denton sorgo is an excellent sweet variety, but it was never popular because the heads bear few seeds.

Scarborough No. 7 broomcorn produces excellent hurl fiber, but the heads have short seed branches. Yield of seed therefore is low, and the cost of its seed is high. Other strains of Scarborough that have poorer hurl fibers but are better seed producers are preferred by most growers of broomcorn seed.

Tift sudangrass and Narragansett alfalfa did not attain the popularity they deserved because the seed yields were lower than those of other varieties. Seedgrowers are reluctant to produce such varieties because the slightly higher price received is insufficient to offset the loss from lower yields of seed.

Birdsfoot trefoil is sown on a smaller acreage than it would be if its harvested seed yields were larger. Yields of seed of birdsfoot trefoil, lupines, reed canarygrass, and some other crops are low mainly because the seeds shatter as they ripen, although other seeds on the plants are not yet mature.

GOOD QUALITY of seed therefore is important in maintaining the popularity of a crop variety.

Club kafir was a productive grain sorghum in Kansas when the field stands were adequate, but its soft seed, which favored seed rots, often produced thin stands and replanting often was necessary. Club kafir therefore was never popular with farmers.

Other crop varieties suffer from seed rots or seedling blights, which interfere with stand establishment.

Hybrid sorghum, which has largely replaced open-pollinated varieties in the United States, often produces better stands than the open-pollinated varieties, chiefly because of greater seedling vigor. This is important when seedbed conditions are unfavorable because of cold soil or the formation of a crust.

Yogo winter wheat is popular in Montana and Wyoming because it was bred particularly for resistance to extreme cold. It also has the capacity to germinate in a drier soil than do other varieties, a characteristic that was recognized after Yogo was widely grown on farms in the drier parts of the West.

Soft, starchy seeds of corn and sorghum are more subject to mechanical injury and to consequent rotting when planted in cool soil than are harder seeds, but they are less likely to require grinding before they are fed to livestock.

Inbred line WF 9 is used in producing a large proportion of the hybrid seed corn planted in the Corn Belt. It is a particularly popular seed parent because it produces a large percentage of medium-flat seed. Seed of this size and shape brings the highest price for planting.

THE SIZE and vigor of a seedling are associated closely with size of seed. In fact, a direct logarithmic relation often exists between weight of seed and the dry weight of the seedling.

Large seeds also permit a seedling to emerge from deeper sowing. Larger seeds thus are particularly important in small-seeded species of forage legumes and grasses. Such seeds must be sown shallow so the seedlings can come up, but then the upper layers of soil may dry out before the seedling is established and the stand may be lost. Large seeds can be sown deep enough to permit the seedling roots to reach moist soil before the upper soil layer is dry.

Because large seeds in tomatoes, cucumbers, okra, eggplant, and watermelon are objectionable to consumers, little attempt may be made to breed varieties with larger seeds to enhance their value for planting.

Seed improvement of crops such as beans, peas, and sweet corn, whose seeds are eaten by people, must give full consideration to food quality as well as suitability for planting.

Temporary dormancy is a desirable characteristic in oats, sorghum, sweet corn, and other crops that are subject to field sprouting in the shock or on the standing stalk before the ripe seed is threshed.

TEMPORARY dormancy is particularly helpful for natural reseeding of crimson clover and other winter annual legumes that mature and drop their seed in early summer. The seedlings that emerge in midsummer quickly perish from the heat, but the ones that come up in the fall usually survive.

On the other hand, dormancy is a handicap in northern winter wheat regions where the crop is sown soon after harvest.

Durum wheat intended for spring sowing often shows a poor germination in laboratory tests for several months after harvest. This dormancy makes it difficult to determine seed quality until shortly before the season for sowing.

Some seeds of certain strains of Hubbard Market and Grand Rapids lettuce remain dormant so long that they do not germinate until several months after harvest.

The presence of many hard seeds that do not germinate promptly in forage legumes such as alfalfa, sweet-clover, and true clovers has imposed difficulties in establishing stands. Hard seeds sometimes are desirable, however, because they retain their viability and may germinate later to reestablish a stand.

Hard, or corneous, seeds of cotton, corn, and sorghum are more resistant to seed rots than are the softer seeded varieties of those crops.

Seed of many grasses, particularly native species, bear awns, hairs or long chaff, which prevent the seeds from passing through the seeding equipment readily.

Home gardeners often have poor stands of lettuce because most of the seed was covered with soil after planting. Certain varieties of lettuce require light for germination, and the buried seeds remain dormant. This light requirement could be eliminated by breeding.

CERTAIN biennial crops, such as sugarbeets and garden beets, and vegetable crops, such as cabbage, celery, lettuce, onion, and spinach, may tend to bolt and produce seed during the crop season. Such plants use food and energy to produce a seedstalk so that the root or top is not worth harvesting. It is essential to breed slow-bolting varieties of these crops, but the plants must be able to bolt during the seed-producing season.

The tendency to bolt under a given environment is controlled by hereditary factors, and the desired bolting characteristics are thus subject to improvement by breeding and selection.

Length of day or temperature or both determine the time at which a plant will bolt and flower. The hereditary makeup of the plant determines its response to light and temperature, but treatment with a chemical like gibberellic acid also may induce the plant to bolt.

THE FOREGOING indicates some of the problems of producing seed, and some of the many accomplishments in improving seed.

One of the achievements is the breeding of the monogerm sugarbeet seed, which eliminates the need to thin the beets by hand. It came about 60 years after its need was recognized. Several varieties and hybrids of monogerm sugarbeets are now in production.

They are descendants of one weak plant that had a single seed in each seedball. It was found in western Oregon in 1948. Plant breeders transferred this monogerm character to productive sugarbeets by crossing, selection, and backcrossing.

Five varieties of crimson clover Dixie, Autauga, Auburn, Chief, and Talledega were selected for hard, dormant seed characteristics that permit the natural establishment of stands in the fall from seed that was dropped in early summer.

IMPROVEMENT in seeds of forage and turf grasses by State and Federal breeders has resulted in varieties with better quality of seed or higher yields of seed.

The improved varieties produce as much forage or more than the unimproved ones. Nordan crested wheat-grass, released in 1953, produces more seed, and the seeds have fewer awns than the unselected type. Its larger seed provides greater seedling vigor. Two other strains of crested wheat-grass with large, awnless seeds were developed also at Mandan, N. Dak., but had not been released in 1961.

Two strains of intermediate wheat-grass, selected in Idaho, appear to have high yields of seed and are nearly free from awns and pubescence. Another selection made in South Dakota offers some improvement in yield of seed.

The Vinall variety of Russian wild-rye yields more seed than the unselected type. The use of Russian wild-rye has been restricted by its low yield and high price of seed.

The Penncross variety of creeping bentgrass, released in Pennsylvania in 1954, produces vigorous plants for putting greens from direct seeding. Tualatin tall oatgrass, released in Oregon in 1940, produces high yields of seed because of its resistance to shattering and to smut.

Butte, Trailway, and Coronado side-oats grama have good yields of large seed, from which grow vigorous seedlings. Butte and Trailway were released in Nebraska in 1958. Coronado was released in Oklahoma in 1955.

The Georgia Selection and Lamont rescuegrasses are good seed producers because they are resistant to smut. Lamont was released in Mississippi in 1957. Lancaster and Lyon smooth bromegrass, which were released in Nebraska in 1950, give high yields of both seed and forage. Lyon also has improved seed quality and strong seedlings. Caddo switchgrass, released in Oklahoma in 1955, gives heavy seed yields if conditions are favorable. Tifhi bahiagrass, released in Georgia in 1957, shatters less than other strains of bahiagrass; more seed thus can be harvested.

Selection for low seed dormancy in green needlegrass has been effective.

SOME DIFFICULTIES have been encountered in efforts to improve the seeds of forage legumes.

Selection for increased percentage of hard seed in a variety of Persian clover has been partly successful. Selection for increased percentage of hard seed of legumes in Canada sometimes has reduced plant vigor.