Chapter 9: Crop Plants and Exotic Plants


Chapter 9: Crop Plants and Exotic Plants


FLAX
Linum usitatissimum L., family Linaceae

Flax is grown in the United States for its seed from which linseed oil is pressed and used primarily in paints. The byproduct, linseed meal, is fed to livestock. More than 2.6 million acres of flax were harvested in the United States in 1969, with an average yield per acre of 750 pounds. There were 1.5 million acres in North Dakota, 652,000 in South Dakota, 388,000 in Minnesota, 100,000 in Texas, 17,000 in Montana, and 3,000 in California. Production per acre within the States varied from 2,240 pounds in California to 700 pounds in North Dakota. The value of the crop was $92.9 million.

In addition to flaxseed, the plant is grown in other countries for its fibrous stalk from which linen is made. Economical U.S. production of fiber flax for linen is not feasible.

Plant:

Flax is a cool-weather crop but grows in warmer climates if it is planted in the fall and harvested at the beginning of the next summer. The plant is a slender annual with small linear leaves and a crown of flowers that later develop into seed pods (fig. 112). The seed flaxes are 15 to 30 inches tall, more branching, and produce more seed than the taller (30 to 48 inches) fiber flaxes.

An average plant produces two to six five-celled pods or capsules, although capable of producing many more. The pod normally produces two seeds in each cell and averages 8.6 seeds per pod (Kozin 1954).

The seeds are planted at the rate of 40 pounds per acre, which provides a high-density plant population necessary for maximum seed production.

[gfx] FIGURE 112. - Seed flax in bloom.

Inflorescence:

Flax flowers are borne on the branch terminals in many-flowered panicles. The petals may vary from white through hues of blue, pink, or lavender (Bailey 1949*). The five petals of the flower unfold at or soon after sunrise, depending upon the temperature, and shed before noon on clear warm days. Flowering continues for several weeks, depending upon soil moisture, but the peak occurs at the end of the first week. New flowers open each day (Knowles et al. 1959).

The five stamens are attached to a fleshy ring at the base of the flower (fig. 113). This ring secretes nectar from five small flat pits on its outer side opposite each stamen (Muller 1883*). The petals are also attached to this ring, alternating with the stamens. They narrow suddenly at the base leaving a round opening between the bases. The anthers of most cultivars are level with the stigmas on the five erect styles, but in some the styles are shorter and in others longer than the stamens (Yermanos and Kostopoulos 1970).

There are four types of flowers in our cultivated flax: the common funnel form, disk shaped with large flat petals, star shaped with narrow in-rolled petals, and tubular flowers.

The flowers are hermaphrodite and slightly protandrous (Eyre and Smith 1916), except for the pollenless male-sterile selections.

Flax provides a small amount of both pollen and nectar for honey bees, the degree of visitation and the material collected apparently depending upon the area and competing floral sources. For example, Scullen and Vansell (1942) considered flax a weak source of both pollen and nectar. Alex (1967) concluded that the bee collected only pollen, and Smirnov (1956) said they collected chiefly nectar. Pellett (1947*) stated the numerous bees are found on flax only where there are large number of colonies in the vicinity.

Smirnov (1956) stated that honey bees visited the blossoms from 7 a.m. to 1 p.m., with most intense visitation between 8 and 11 a.m. He concluded that, because the petals shed so easily soon after they open, particularly when a bee alights upon one, the bee "learns" to alight below the calyx and extend its proboscis between the petal bases from below to obtain the nectar. Such visitation contributes nothing to pollination, the contribution coming only before the bee adapts the new collecting stance.

[gfx] FIGURE 113. - Flax flower, x 3. A, Longitudinal section; B, flower with perianth removed to show nectaries.

Pollination Requirements:

Flax is considered to be normally self-pollinated although some crossing (1 to 6 percent) occurs (Dillman 1938, Dillman and Stoa 1935, Dillman and Goar 1937, Masuo 1958, Robinson 1937), mostly among the large flowered types. Rubis (1970) worked with a male-sterile line having disk-form flowers, and stated that he obtained practically no cross- pollination of the male-sterile lines with lines having tubular flowers; however, good seed set was obtained, indicating heavy cross-pollination, with other lines that had large disk-form flowers.

Self-pollination is influenced by the position of the anthers in relation to the stigmas. If the anthers are above or below the level of the stigmas, there is increased opportunity for cross-pollination (Yermanos and Kostopoulos 1970). In most commercial cultivars, however, they are on the same level. For a brief period after this type of flower opens, there is space between the anthers and the stigma. This permits cross- pollination to occur if foreign pollen is brought to the stigma. Whether or not cross-pollination occurs, the stamens soon bend inward so their pollen touches the stigma and self-pollination results. Flax is another example of plants that offer opportunity for cross-pollination then provide for selfing for survival of the species (Mtiller 1883*).

Several tests have shown that bee pollination improves seed yields in fiber flax. Bezdenezhoykh (1956) in Russia reported that honey bees in cages increased seed production of fiber flax 22.5 percent over plants in cages without bees. Gubin (1945) also studied the effect of bee pollination of fiber flax in Russia and reported that bees increased seed production 22.5 to 38.5 percent. Luttso (1957), also in Russia, reported that bee pollination increased seed production by 29 percent, the number of seeds per capsule by 18 percent, and the weight per seed by 11 percent in comparison to fields without bee pollination. Likewise, Smirnov (1956) showed a 19 percent increase in the number of seeds per capsule, a 22 percent increase in the total weight of seeds, and a 2.2 percent increase in the weight per seed. He also reported that bee-visited plants set up the crop and ceased blooming earlier than plants from which bees were excluded. The reason for the increased size of the seed in addition to seed number was not explained. Usually, when more seeds are produced by a plant, the size of the individual seed decreases.

The influence of bee pollination on oilseed flax is somewhat different. Hassanein (1955) reported that honey bee pollination increased both "quantity and quality" of seeds. However, Pritsch (1965) and Alex (1957) failed to show any benefit in terms of increased seed production, and insect pollination is generally considered unnecessary on U.S.-grown flax.

Shehata and Comstock (1971) discussed the potentials for increased production with hybrid vigor in flax. They obtained an average of 6 percent increase in production with hybrids over the highest yielding cultivar, and they stated that interest in hybrid flax is increasing. For the production of hybrid seed, the pollen must be transferred from the fertile to the male- sterile lines.

Pollinators:

Eyre and Smith (1916) pointed out that flax pollen is produced only in small quantities and is not the windblown type, so they concluded that cross-pollination was entirely by insects.

Dillman (1938) mentioned bumble bees as visitors along with honey bees, and Henry and Chih (1928) mentioned honey bees, a "small bee," and thrips, believing that the last-mentioned insects were important agents in cross-pollination in India. Hassanein (1955) attributed 90 percent of the crossing in flax to honey bees; Smirnov (1954), 26 to 93 percent; and Alles (1961), Bezdenezhnykh (1956), Luttso (1957), and Smirnov (1954) concluded that honey bees were the most important agents. When the honey bee collects pollen, it cannot fail to transfer pollen to the stigmas. This is also true when nectar is collected in the normal way.

Pollination Recommendations and Practices:

Alles (1961) concluded that the number of honey bee visits per flower of fiber flax has a determining effect on flax seed set and weight, but he gave no indication as to how many bees were needed. Kozin (1954) reported a sizeable increase in seeds per boll and seed weight when 40 colonies were placed near a fiber flax field, but he did not indicate the size of the field. Also, he stated that there were 226 bees per hectare (90 bees per acre), which seems to be an extremely low population for the number of flowers per acre. Gubin (1945) indicated that each flower of fiber flax should receive an average of two honey bee visits. This is the most concrete recommendation for the use of bees on flax. Whether it applies equally to fiber and seed flaxes is unknown.

There have been no recommendations for the placement and use of honey bees as pollinators of seed flax in this country. The evidence indicates, however, that if hybrid seed is produced insect pollinators will be needed, of which honey bees seem to be the best. The number of bee colonies that would be necessary in or around such a field to provide adequate pollination is unknown. Because the plant is not overly attractive to bees, the relative number of colonies needed would be large if competing plants were in bloom. The breeders might devote some attention to the relative attractiveness of cultivars with the thought in mind that if hybrid seed production materializes and bees are utilized the incorporation of lines having greater attractiveness could improve the efficiency of hybrid seed production.

LITERATURE CITED:

ALEX, A. H. 1957. POLLINATION OF SOME OILSEED CROPS BY HONEY BEES. Tex. Agr. Expt. Sta. Prog. Rpt. 1960, 5 pp.

ALLES, P. T.

1961. INFLUENCE OF THE MIXTURES OF FLOWER POLLEN, OF MICROELEMENTS AND OF VITAMIN B IN THE PROCESS OF FORMATION OF THE SEEDS OF DIFFERENT VARIETIES OF SUNFLOWER AND FLAX. In 18th Internatl. Apic. Cong. Proc., Madrid, Summaries of the Congress: 5-6. BEZDENEZHNYKH, S. M. 1956. POLLINATION OF FIBER FLAX AND TRAINING OF BEES. ] In Krishchunas, I. V., and Gubin, A. F., eds. Pollination of Agricultural Plants. Moskva, Gos. Izd-vo. Selkhoz Lit-ry, pp. 21-24. [In Russian.] DILLMAN, A. C. 1938. NATURAL CROSSING IN FLAX. Amer. Soc. Agron. Jour. 30: 279 - 286. ______and GOAR, L. G. 1937. FLAXSEED PRODUCTION IN THE FAR WESTERN STATES. U.S. Dept. Agr. Farmers' Bul. 1792, 22 pp. and STOA, T. E. 1935. FLAXSEED PRODUCTION IN THE NORTH CENTRAL STATES. U.S. Dept. Agr. Farmers' Bul. 1747, 18 pp. EYRE, J. V., and SMITH, G. 1916. SOME NOTES ON THE LINACEAE, THE CROSS POLLINATION OF FLAX. Jour. Genet. 5: 189-197. GUBIN, A. F. 1945. CROSS POLLINATION OF FIBRE FLAX. Bee World 26(4): 30, 31. HASSANEIN, M. H. 1955. THE VALUE OF POLLINATING INSECTS TO FLAX SEED PRODUCTION IN EGYPT. Agr. Sci. Ann. [Cairo]: 773 - 784. [In English, Arabic summary.] HENRY, A. W., and CHTH, Tu. 1928. NATURAL CROSSING IN FLAX. Amer. Soc. Agron. Jour. 20: 1183 - 1192 KNOWLES, P. F., ISOM, W. H., and WORKER, G. F. 1959. FLAX PRODUCTION IN IMPERIAL COUNTY. Calif. Agr. Expt. Sta.-Agr. Ext. Sen. Cir.480,27 pp. KOZIN, R. B. 1954. [INFLUENCE OF BEES ON THE SEED YIELD OF FIBER FLAX.] Pchelovodstvo 31 (6): 41-43. [ In Russian. ] AA-204/56. LUTTSO, V. P. 1957. [THE POLLINATION OF FLAX BY HONEY BEES.] Dokl TSKhA 30: 327-331. [In Russian.] AA-276/61. MASUO, Y. 1958. [ON NATURAL CROSSING IN FLAX.] Crop Sci. Soc. Japan Proc. 27: 321-323. [In Japanese.] Abstract in Plant Breed. 29(4): 817-818. Oct. 1959. PRITSCH, G. 1965. [INCREASING THE YIELD OF 0IL PLANTS BY USING HONEY BEES.] Ved. Prace vyzkum. Ustav. Vcelar CSAZV 4: 157-163. [In German.] AA-770/66. ROBINSON, B. B. 1937. NATURAL CROSS-PoLLINATION STUDIES IN FIBER FLAX. Amer. Soc. Agron. Jour. 29(8): 644 - 649. RUBIS, D. D. BREEDING INSECT-POLLINATED CROPS. In The Indispensable Pollinators, Ark. Agr. Ext. Sen. Misc. Pub. 127, pp. 19 - 24. SCULLEN, H. A., and VANSELL, G. H. 1942. NECTAR AND POLLEN PLANTS OF OREGON. Oreg. Agr. Expt. Sta. Bul. 412, 63 pp. SHEHATA A. H., and COMSTOCK, V E. 1971. HETEROSIS AND COMBINING ABILITY ESTIMATES IN F2 FLAX POPULATIONS AS INFLUENCED BY PLANT DENSITY. Crop Sci. 11: 534 - 535. SMIRNOV, V. M. 1954. [CROSS-POLLINATION OF FLAX BY BEES.] Pchelovodstvo (9): 53 - 55. [In Russian.] Abstract in Bee World 37: 124. ______ 1956. [CROSS-POLLINATION OF FIBER FLAX WITH THE AID OF BEES.] In Krishchunas, I. V., and Gubin, A. F., eds. Pollination of Agricultural Plants. MoskVa, Gos. Izd-vo. Selkhoz Lit-ry, pp. 16-21. [In Russian.] YERMANOS, D. M., and KOSTOPOULOS, S. S. 1970. HETEROSTYLY AND INCOMPATIBILITY IN LINUM GRANDIFL0RUM DESF. In The Indispensable Pollinators, Ark. Agr. Ext. Sen. Misc. Pub. 127, pp. 50 - 54.


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