SCARLET RUNNER BEAN
Phaseolus coccineus L., family LeguminosaeThe scarlet runner bean, or runner bean, native to Mexico or Central America (Graham 1941*) and of major importance in parts of Europe, is of minor importance in the United States, where it is sometimes called the Oregon lima bean.
Plant:
The roots of the slender, twining scarlet runner bean are tuberous and live for several years, but frost kills the aerial part; therefore, it is an annual plant above the ground, but a perennial beneath (Kooistra 1968). The plant may grow to a height of 10 to 15 feet if staked, but when grown commercially the crop is not staked. It is harvested by the same method used in harvesting lima beans, with yields of 1,200 to 1,500 lb/acre of seed (Hawthorn and Pollard 1954*).
Inflorescence:
The showy blossoms are borne on long racemes. They are attractive to various species of bees for both nectar and pollen. Darwin (1874) showed that the blossom is ingeniously contrived to insure that insect visitation results in pollination. This is brought about by a pair of nectar holes at the base of the staminal tube, almost covered by a flap on one stamen. When the bee forces this flap aside, it rubs across the staminal column and transfers pollen from anthers to stigma.
Pollination Requirements:
Darwin (1889*) covered scarlet runner beans to exclude pollinating insects and obtained only one-eighth and one-third as many beans as were obtained from open plants. In a more elaborate experiment, Free (1966) caged scarlet runner beans with and without honey bees to determine the need for insect pollination. Plants caged with bees set 1,479 g of pods per plant, compared with 180 g per plant where bees were excluded. Other factors varied correspondingly: Pods per plant, 96:11; grams of seed per plant, 356:50; number of seeds, 206: 30; and seeds per pod, 3.9 in bee cages compared to 2.7 in cages where bees were excluded. Only the mean weight per seed was unchanged. The pods in the cages without bees could not be harvested until later in the season than those in the bee cages. Tedoradze (1959) obtained similar benefits from bees.
Mommers (1971) studied the pollination of runner beans under glass and reported that bees had no effect on production of beans. He concluded that varietal differences influenced the results obtained by Free (1966), and that this accounted for the differences reported.
Pollinators:
Henslow (1878) showed that bumble bees pollinated scarlet runner beans. Free and Racey (1968) showed that honey bees were as useful as bumble bees in pollination of scarlet runner beans grown in glass houses, although Free (1968) found that individual bumble bees worked faster and visited more flowers per plant than did honey bees. Bumble bees often pierce a hole in the base of the flower and steal the nectar without contributing to pollination. Subsequently, honey bees visit this hole and again pollination is bypassed (Jany 1950).
Pollination Recommendations and Practices:
Blackwall (1964) said that adequate pollination is a must for early yields and that lack of insect pollination is the most important single cause for low yield of beans. Blackwall also stated that where lack of pollination is a recurrent problem, it may be worthwhile to hire colonies of honey bees to supplement the local pollinator population. She recommended that beekeepers supply small, rapidly expanding colonies, which have a high need for pollen.
Free (1966) stated that because honey bees are clearly effective in pollinating scarlet runner beans, their use should increase yields where pollination is a limiting factor. However, he did not make a recommendation to growers on the use of honey bees as pollinators of this crop. The evidence indicates, however, that if the grower wants to obtain maximum yields and harvest the seeds as early as possible, he should have a high pollinator population in his field, particularly during early flowering.
LITERATURE CITED:
BLACKWALL, F. L. C.
1964. RUNNER BEANS: ADEQUATE POLLINATION IS A MUST FOR EARLY YIELDS. Grower 61: 1272-1273.DARWIN, F.
1874. BEES VISITING FLOWERS. Nature 9: 189-190.FREE, J. B.
1966. THE POLLINATION OF THE BEANS PHASEOLUS MULTIFLORUS AND PHASEOLUS VULGARIS BY HONEYBEES. Jour. Apic. Res. 5: 87-91.______ 1968. THE BEHAVIOUR OF BEES VISITING RUNNER BEANS (PHASEOLUS MULTIFLORUS). Jour. Appl. Ecol. 5: 631-638.
______and RACEY. P. A.
1968. THE POLLINATION OF RUNNER BEANS (PHASEOLUS MULTIFLORUS) IN A GLASSHOUSE. Jour. Apic. Res. 7: 67-69.HENSLOW, G.
1878. THE FERTILIZATION OF THE SCARLET RUNNER BEAN BY BUMBLE- BEES. Gard. Chron., n.s., 10: 561.JANY, E.
1950. [THE PIERCING OF SCARLET RUNNER FLOWERS BY BUMBLE BEES.] Ztschr. f. Angew. Ent. 32(2): 172-183. [In German.] AA-45/54.KOOISTRA, E.
1968. SELECTION IN RUNNER BEANS (PHASEOLUS CONCINNUS) WITH SPECIAL REFERENCE TO THE USE OF TUBEROUS ROOTS. Euphytica 17: 183-189.MOMMERS, J.
1971. [THE POLLINATION OF BEANS PHASEOLUS UNDER GLASS.] Maandschr. v. de Bijent. 73(5): 79-80. [In Dutch English summary.]TEDORADZE, S. G.
1959. [THE ROLE OF BEES IN THE SHAPE-FORMING PROCESS OF [SCARLET RUNNER] BEANS UNDER GEORGIAN CONDITIONS.] Pchelovodstvo 36(9): 40-42. [In Russian.]
