BEAN15
Phaseolus vulgaris L., family LeguminosaeThe common bean includes the edible fresh, and processed, green snap, green-shelled, and dry beans. In 1969, about 1,872,000 acres were devoted to the many types and scores of cultivars of beans, which had a farm value of more than $243 million. Fresh snap beans are primarily produced in Florida and along the eastern seaboard; processed beans, in New York, Oregon, and California, and along the eastern seaboard. Dry beans are produced in two main areas, in the West (Idaho, Colorado, and New Mexico) and in north central U.S. (in and around Michigan).
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15 See also: "Broad Bean and Field Bean," pp.117; "Lima Bean," p. 244; and "Scarlet Runner Bean," p. 332.Plant:
The vast majority of P. vulgaris cultivars are bush type annuals that reach a height of about 2 1/2 feet and are grown in rows about 3 feet apart. The leaves are dense, heart-shaped, and 3 to 6 inches long. The fruit is a pod, straight or slightly curved, 4 to 8 inches long, with a prominent beak. The seeds may be white to red, brown speckled, or blue-black; globular to oblong; and from l/4 to 1 inch long. Pods may contain from one to a dozen seeds.
Inflorescence:
The bean flower is of the typical legume shape; usually whitish, but may be tinged to deep violet, purple, or red; and is l/2 to 3/4 inch long. The keel is prolonged in a spirally twisted beak. The style follows the spirals of the keel. There are the usual 10 stamens, the upper one free while the other nine are united into a tube enclosing the long ovary and part of the style. The blooms are loosely scattered along a 2- to 3-inch rachis (stem). They usually open between 7 and 8 a.m., and never close. The corolla sheds after a few days. The anthers dehisce the evening of the day before the flower opens (Jones and Rosa 1928*). Weinstein (1926) reported that many pollen grains germinate in the anther, but whether such pollen plays a part in fertilization is unknown. Knuth (1908*, p. 339) stated that although the anthers surround the style and the pollen is released before the flower opens, the pollen does not get onto the stigma before tripping occurs. When pressure, for example, the weight of a large bee, is applied to the wing petals, the style, with pollen adhering to the brush of hairs on it, projects from the tip of the keel. When pressure is released, the style retracts into the keel, sometimes leaving some pollen exposed.
When the stigma is first exposed, it is free of pollen, and may touch a pollen-coated bee during its brief period of exposure. If this happens, cross-pollination can occur. As the stigma retracts into the keel, it comes in contact with the pollen released by the anthers and selfing may also occur. Bean breeders state that beans excluded from insect visitors set a full complement of pods and seeds, although there seems to be no data on the relative time interval required for isolated plants and for bee-visited plants to accomplish this.
Pollination Requirements:
Bean breeders state that they plant different lines and cultivars alongside each other without fear of cross-pollination, indicating very reliable self-pollination. The flowers of most bean cultivars are capable of self-pollination although cross-pollination can and does occur to varying degrees, depending upon the cultivar and the pollinator population (Hawthorn and Pollard 1954*, Mackie and Smith 1935, Barrons 1939). Much of the research on bean pollination has been concerned only with the impact of the cross-pollination on varietal seed contamination, not on quantity or quality of fruit set. Rutger and Beckham (1970) stated that P. vualgaris is primarily a selfing species, but studies of controlled insect pollination are needed. Free (1966) concluded that the pollination requirements of different species of beans could not be predicted so they must be studied individually. Thorough studies on the possible benefits of maximum pollinator activity on the various types and cultivars would appear to be highly worthwile.
Darwin (1857) noted that the movement of the pistil by the bee would appear to aid in the fertilization of the flower by its own pollen. When he tested this effect, he found that flowers not disturbed in any way set no seed, but flowers manipulated by the wing petals set a great number of seeds. From this, he deduced that "if every bee in Britain were destroyed, we should not again see a pod on our kidney beans." Just what species or cultivar he dealt with is not clear.
Knuth ( 1908 *, p. 339) stated that the anthers surround the style and shed their pollen upon it, but the stigma is never dusted until the keel is depressed. Then the style, with its pollen-covered brush, springs out of the opening. If the stigma is touched by the bee, coated with pollen from other plants, before being contacted by its own pollen, cross-pollination results. However, Taylor ( 1919) stated that the flowers are entirely self-fertile as is abundantly proved by their productiveness when grown in greenhouses where bees are not present. Yet, he stated that they can be cross-fertilized by bees, although the percentage of crossing is not great. Mackie and Smith (1935) and Barrons (1939) indicated that cross- pollination may amount to more than 8 percent. The pollinator population associated with the crossing was never measured.
Jones and Rosa (1928*) stated that because the stigma and the anthers are enclosed within the keel, insects reach them only with difficulty; however, visitation occurs and crossing results. They considered the- amount negligible. They also stated that selfing occurs freely when flowers are enclosed. Kristofferson (1921) reported 0 to 1.4 percent crossing, and Emerson (1904), 0 to 10 percent crossing. Free (1966) working with 'Processor' cv. of P. vulgaris concluded that "honey bees are unlikely to have much effect on the yield." His data, however, showed that the plants in the cages with bees produced 21 percent more seed weight, with 6 percent more pod weight than plants from which bees were excluded.
Beans are visited only sparingly by honey bees, and beekeepers do not consider this crop of significance as a source of nectar or pollen. What the visitation or its effect on beans might be under a high concentration of bees is unknown, but the information would be of interest and possibly of considerable value to bean growers.
Pollinators:
Mommers (1971 ) studied the pollination of beans grown under glass and concluded that bees do not influence development of P. vulgaris.
Diwan and Salvi (1965) stated that beans in India are eagerly visited by Apis dorsata, A. florea, and Trigona spp., but the flowers are generally ignored by A. cerana. Those who have studied the problem agree that bumble bees and honey bees are the most frequent visitors to bean flowers in the United States. Darwin (1858) and Palmer (1967) indicated that bees are of benefit to beans, but the kind of bean they referred to is not clear. The data indicate that, if pollinating insects are of benefit, the bumble bee is the best pollinator. Honey bees are apparently next in importance. The latter can be increased in numbers where desired. They visit the blossom for both pollen and nectar. The exact effect on the flower or value to the different cultivars of P. vulgaris has not been well established.
Pollination Recommendations and Practices:
There are no recommendations on the use of bees as pollinators of beans. In fact bean breeders, knowing the plants will set fruit in greenhouses where bees are excluded, feel that pollinating insects are entirely unnecessary. On the other hand, some growers "like to see bees around," believing that their activity results in fuller pods. For such an important crop, more precise information should be obtained on its pollination requirements, and the possible value of pollinating insects. The effect of saturation pollination, as practiced on other crops, might be effective.
LITERATURE CITED:
BARRONS, K. C.
1939. NATURAL CROSSING IN BEANS AT DIFFERENT DEGREES OF ISOLATION. Amer. Soc. Hort. Sci. Proc. 36: 637-640.DARWIN, C. [R.]
1857. BEES AND FERTILIZATION OF KIDNEY BEANS. Gard. Chron. 45: 725.____ 1858. ON THE AGENCY OF BEES IN THE FERTILIZATION OF PAPILIONACEOUS FLOWERS AND ON THE CROSSING OF KIDNEY BEANS. Gard. Chron. 46: 828-829.
DIWAN, V. V., and SALVI, S. R.
1965. SOME INTERESTING BEHAVOURIAL FEATURES OF APIS DORSATA FAH. Indian Bee Jour. 27(1): 52.EMERSON, R. A.
1904. HEREDITY IN BEAN HYBRIDS (PHASEOLUS VULGARIS). Nebr. Agr. Expt. Sta. Ann. Rpt. 17: 33-68.FREE, J. B.
1966. THE POLLINATION OF THE BEANS PHASEOLUS MULTIFLORUS AND PHASEOLUS VULGARIS BY HONEYBEES. Jour. Apic. Res. 5: 87-91.KRISTOFFERSON, K. B.
1921. SPONTANEOUS CROSSING IN THE GARDEN BEAN, PHASEOLUS VULGARIS Hereditas 2: 395-400.MACKIE. W. W., and SMITH, E. L.
1935. EVIDENCE OF FIELD HYBRIDIZATION IN BEANS. Amer. Soc. Agron. Jour. 27: 903-909.MOMMERS, J.
1971. [THE POLLINATION OF BEANS UNDER GLASS (PHASEOLUS)]. Maandschr. v. de Bijent. 73(5): 79-80. [In Dutch, English abstract.]PALMER, R.
1967. BEES AID BEAN POLLINATION. So. African Bee Jour. 39(4): 12-13.RUTGER J. N., and BECKHAM, L. S.
197O. NATURAL HYBRIDIZATION OF PHASEOLUS VULGARIS X P. COCCINEUS L. Amer. Soc. Hort. Sci. Proc. 95: 659-661.TAYLOR, W. H.
1919. BEES AND FLOWER FERTILIZATION. New Zeal. Jour. Agr. 18: 203.WEINSTEIN, A. I.
1926. CYTOLOGICAL STUDIES ON PHASEOLUS VULGARIS. Amer. Jour. Bot. 13: 248-263.