RASPBERRY
Rubus spp., family RosaceaeThe commercial cultivated raspberries include the red raspberry of Europe (R. idaeus L.), the red (R. strigosus Michx.) and black (R. occidentalis L.) wild raspberries of North America, and the purple raspberry, which was developed here as a cross between R. strigosus and R. Occidentalis (Darrow 1937).
In 1971, the estimated production of raspberries in frozen commercial pack was 28 million pounds, most of which came from Oregon, Washington, and the northern Midwest. This does not include production in home gardens for fresh use or for frozen food lockers. Production ih the above two States from 8,730 acres in 1969 amounted to 39 million pounds valued at $11.2 million (USDA 1971).
Plant:
Raspberry roots may live for years, but the "cane" or stem lives only 2 years. Usually, the cane growth is attained the first year, then the fruit is produced the second year, after which the cane dies. Some kinds produce a fall crop on the terminals of current season canes (Magness et al. 1971). Red and purple raspberry canes may reach a height of 8 feet. They are upright or semierect. Black raspberries, or black caps, have arched canes that reach 4 to 5 feet and form roots at the tips. Hybridization of the species has produced many variations in the growth habits of these plants. The thorns or spines on the stems vary from strong and sharp to scattered weak prickles or none. The leaves are usually deciduous (USDA 1967).
The fruit, a berry, consists of many one-seeded drupelets or carpers on the receptacle. When the fruit is harvested, the receptacle remains on the plant, leaving the fruit as a more or less hollow cap (Bailey 1949*).
Inflorescence:
The raspberry flower is about 1 inch in diameter and has five whitish petals, many stamens inserted on the calyx, and many ovaries, each with a slender terminal style usually remaining on the drupelet. The flowers are mostly bisexual (Eaton et al. 1968).
When the flower opens, the anthers are immature, with the filaments bent over the immature styles (fig. 167). Subsequently, the outer stamens bend back toward the petals and their anthers dehisce. As dehiscence progresses toward the center of the flower, the receptacle expands, the styles grow, and the receptive stigmas appear at their tips; later, the anthers nearest the stigmas dehisce, and, if cross-pollination has not already been brought about by insects, some selfing may result. The degree of such selfing seems to vary with species and cultivar, but most of them are largely self-sterile.
A day or so after the flower opens, the petals begin to shed. Flowering on a plant may occur over 1 to 3 weeks. Nectar is secreted abundantly by a fleshy ring on the margin of the receptacle (inside the ring of stamens) (Knuth 1908*, p.351). The rich and copious nectar (13 mg per flower) (Haragsimova-Neprasova 1960, Petkov 1963) as well as the pollen are highly attractive to insects. Commercial production of a high quality, much sought after raspberry honey occurs in some Northern States and Canada.
[gfx] FIGURE 167. - Longitudinal section of 'Willamette' raspberry flower, x 10.
Pollination Requirements:
Wellington (1913) and Hardy (1931) concluded that the raspberry is self-fertile, and that the pollen fertilizes the stigma before the flower is open. Other research has shown that they reached erroneous conclusions. Johnston (1929) showed that only 16 to 70 percent of the flowers produced berries when insects were excluded, as compared to 64 to 98 percent that set when the blossoms were exposed to pollinating insects. Couston (1963, 1966) compared production of a few plants caged to exclude pollinating insects with plants exposed to insect visitation. Fruit developed on plants of both treatments, but on the caged plants the size of the berries was so small (half the size of those on the open plants) and the volume of fruit produced was so low (one-third less) that it was not worth harvesting commercially. When the 'Malling Jewel' cv. was caged against insects, it produced almost no berries, but plants caged with a colony of honey bees yielded better than those in the open. Couston concluded that raspberries can be pollinated by honey bees alone, without other insects if necessary.
Shanks (1969) used cages over raspberries with and without colonies of honey bees enclosed. He found that the fruits had 71 to 82 percent fewer drupelets in the absence of bees, and that wind was not a factor in raspberry pollination. The fruit that set in the beeless cages was distinguished by a tuft of unpollinated pistils on the end of each berry. He considered the honey bee of primary importance in the pollination of raspberries in Washington. Allen (1937) stated, without supporting data, that raspberry bushes ". . . bear but little fruit unless there are some bees in the neighborhood." Likewise, Smith and Bradt (19678) stated without supporting data, that raspberries and blackberries are self-fruitful but require bees for pollen transfer.
In a well-conducted test, Eaton et al. (1968) showed the value of repeated bee visits in producing more and larger red raspberries. They emasculated the flowers, treated the stigmas to different pollen applications, and recorded the results in terms of fruit set and drupelets per fruit. Their results are shown in table 15.
[gfx] fix table 15:
TABLE 15. - Value of repeated bee visits in producing red raspberries __________________________________________________________ Treatments ____________________________ Fruit set and size 11 22 33 44 55 __________________________________________________________ Mean number of fruits set of 5 flowers 1.0 2.7 2.8 3.8 4.2 Mean number of drupelets per fruit 5.3 21.5 35.0 38.3 40.0 __________________________________________________________ 1No pollen applied to stigma. 2 Pollen applied once, immediately after emasculation. 3 Treated same as treatment 2, then poHen was applied again on the following day. 4 Treated same as treatment 3, then pollen was applied again on the 3d day. 5 Treated Same as treatment 4, then pollen was applied again on the 4th day.
The results showed that for the largest number of berries with the most drupelets, each flower should be repeatedly visited by bees for at least 4 days.
Pollinators:
Honey bees are the best pollinating agents of raspberries. Because honey bees and raspberries are mutually benefited, these insects should be given major consideration as pollinators of raspberries.
Pollination Recommendations and Practices:
None of the research workers who have studied the pollination requirements of raspberries have recommended that steps be taken to increase the pollinator population on the raspberry since Hooper (1913) made the general statement that raspberries need insect pollination. He recommended one colony for each 2 acres. The evidence is plain that the plant requires or at least is greatly benefited by such pollination. Where the crop is grown commercially with its vast numbers of blossoms calling for insect transfer of pollen from anthers to stigmas, whether on the same flower, flowers of the same plant, or between plants, bees should be supplied to the plantings. The grower is interested in the largest possible berries as well as maximum production. This can only be obtained with ample insect pollinators.
No studies have been made on the number of bee visitors per flower that result in maximum pollination, although Eaton et al. (1968) showed that the flowers should be visited for at least 4 days. The anthers are not all open at the same time nor are all of the stigmas receptive at once. Thus, repeated bee visits are quite probably necessary if all of the ovules are to be cross-pollinated and a well-formed berry is to be harvested. Until real evidence is available, one can only compare bee activity and floral structure of other plants in estimating the bee activity desired. By this method, a desired bee population of about one bee visitor for each 100 open blossoms would appear logical. The colonies per acre necessary to supply this visitation would depend on the acreage of berries involved, competing plants, colony strength, and many other factors. The importance and value of the bees is so great that quite likely several colonies per acre would be justified.
LITERATURE CITED:
ALLEN, M. Y.
1937. EUROPEAN BEE PLANTS. 148 pp. Bee Kingdom League, Alexandria, Egypt.COUSTON, R.
1963. THE INFLUENCE OF INSECT POLLINATION ON RASPBERRIES. Scot. Beekeeper 40: 196-197.______ 1966. EXPERIMENTS ON THE INFLUENCE OF INSECT POLLINATION ON SOFT FRUITS. Scot. Beekeeper 43(3): 39-40, (5): 90-92.
DARROW, G. M.
1937. BLACKBERRY AND RASPBERRY IMPROVEMENT. U.S. Dept. Agr. Yearbook 1937: 496-533.EATON, G. W., DAUBENY, H. A., and NORMAN, R. C.
1968. POLLINATION TECHNIQUES FOR RED RASPBERRY BREEDING PROGRAMS. Canad. Jour. Plant Sci. 48(3): 342-344.HARAGSIMOVA-NEPRASOVA, L.
1960. [MEASUREMENT OF NECTAR SECRETION IN PLANTS.] Ved. Prace Vyzkum. Ustav. vcelar CSAZV 2: 63-79. [ln Czech., English and other summaries.]HARDY, M. B.
1931. SELF AND CROSS FERTILITY OF RED RASPBERRY VARIETIES. Amer. Soc. Hort. Sci. Proc. 28: 118-121.HOOPER, C. H.
1913. THE POLLINATION AND SETTING OF FRUIT BLOSSOMS AND THEIR INSECT VISITORS. Roy. Hort. soc. Jour. 38: 238-248.JOHNSTON, S.
1929. INSECTS AID FRUIT SETTING OF RASPBERRY. Mich. Agr. Expt. Sta. Quart. Bul. 11(3): 105-106.MAGNESS, J. R., MARKLE, G. M., and COMPTON, C. C.
1971. FOOD AND FEED CROPS OF THE UNITED STATES - A DESCRIPTIVE LIST CLASSIFIED ACCORDING TO POTENTIALS FOR PESTICIDE RESIDUE. N.J. Agr. Expt. Sta. luterregion. Res. Proj. lR-4, IR Bul. 1, 255 pp.PETKOV, V. [G.]
1963. [NECTAR PRODUCTION IN CULTIVATED RASPBERRY.] Sell Nauk. 2: 201-207. [In Bulgarian, Russian and English summaries.] AA-495/66.SHANKS, C. H., JR.
1969. POLLINATION OF RASPBERRIES BY HONEYBEES. Jour. Apic. Res. 8: 19-21. UNITED STATES DEPARTMENT OF AGRICULTURE. 1967. GROWING RASPBERRIES. U.S. Dept. Agr. Farmers' Bul. 2165, 14 pp.______ 1971. FRUITS. PART 1 NON-CITRUS BY STATES, 1969 - 7O, PRODUCTION USE VALUE. U.S. Dept. Agr. Statis. Rptg. Serv. CRB, FRNT 4-1 (5-71), 22 PP.
WELLINGTON, R. [A.]
1913. RASPBERRY BREEDING. Amer. Soc. Hort. Sci. Proc. 10th Ann. Mtg., pp. 155-159.
