CUCUMBER AND GHERKIN
Cucumis sativus L., family CucurbitaceaeCucumbers and gherkins are grown in most of the States to some extent but over half of the 179,400 acres devoted to this crop in 1969 was in five States: North Carolina (34,100), Michigan (23,100), Wisconsin (13,900), Florida (16,400), and Texas (10,900). The 1969 crop was valued at $78 million, of which $32 million was derived from cucumbers marketed in the fresh state and $46 million from processed cucumbers.
The so-called gherkin of American commerce is a small-fruited cucumber type processed in a special way. The true gherkin, or West Indian gherkin, is another species (C. anguria L.). It is grown primarily in Brazil and occasionally in the West Indies. Its fruit is somewhat oval rather than oblong like the cucumber (Purseglove 1968 *).
Plant:
The cucumber is a trailing or climbing, normally monoecious, annual herb, with vines 2 to 10 feet long covered with stiff bristly hairs. The roughly triangular leaves are 3 to 10 inches across, and they are supported on 3- to 7-inch petioles or stems, which permit the leaves to overshadow the prostrate branches, flowers, and fruit (Whitaker and Davis 1962*).
Chao-Shan and Humphries (1969) studied fruit setting on the vines of three cultivars in North Carolina, and found that 75 to 90 percent of the fruit set within 20 inches, and the bulk with 12 inches, of the crown.
Two main types of fruit are grown commercially in the United States - the slicing- or salad-type cucumber and the pickling cucumber. The two types have been developed for their specific uses and differ in production methods.
The fruit is pendulous and oblong and has a relatively large stem. Particularly when young, its skin has spiny, wortlike tubercles. It has a characteristic odor and taste that make it not too palatable alone, but delicious in salads. The majority of the fruit is consumed as processed pickles.
The plant requires warm weather but not as hot as that required by watermelons. Some crops of salad-type cucumbers are grown under glass in cold countries to supply off-season demands for the fresh fruits. Greenhouse cucumbers are usually more uniform than fieldgrown ones, primarily because of better control of plant growth and environmental conditions including insect pollination. An estimated 20 percent of the pickling cucumbers were machine harvested in 1967, and the percentage is increasing (Zahara and Sims 1966, Sims and Zahara 1968).
In Europe, and to some extent in the United States, a special slicing cucumber sets fruit parthenocarpically (without pollination) (Strong 1931, Whitaker and Jagger 1937). It sets no seed unless pollinated. If seeds are produced they detract from its eating quality (Kettner 1967). In some areas in Europe where this cucumber is grown, beekeepers are required to remove their bees from the area during the flowering period (Milne 1941, van Berkel 1960, van Berkel and Vriend 1957, van Koot 1960). In such areas, the planting of phacelia is recommended so that it flowers simultaneously with this cucumber and lures the bees from the cucumber flowers (Proefstation Voor de Groentenen Fruitteelt onder Glaste Naaldwijk 1958).
Inflorescence:
Cucumber flowers are axillate and quite similar to those of muskmelons. The staminate ones are borne in clusters, each flower on a slender peduncle or stem. The pistillate ones are usually borne solitary on a stout peduncle. As in other cucurbits, the pistillate flower is easily recognized by the large ovary at the base of the flower. In the muskmelon, the ovary is covered with soft hairs, but in the cucumber it is sparsely covered with spiny wortlike growths. The yellow, wrinkled petals are similar in size and shape to those of the muskmelon. The pistillate flower has three thick stigma lobes atop a short broad style (Heimlich 1927). Normal cucumber types have staminate and pistillate flowers in varying proportions depending on plant growth, vigor, and environmental conditions.
The staminate flowers (fig. 103) usually appear about 10 days before the first pistillate flowers appear (Judson 1929). They normally out-number the pistillate flowers about 10 to 1 (Alex 1957), but this ratio has been known to reach 100 to 1, and there are seasonal variations in the ratio (Currence 1932, Edmond 1931). This ratio can be altered also by the application of certain pheromone chemicals (McMurray and Miller 1968, Robinson et al. 1968, Sims and Gledhill 1969).
In the recently developed "gynoecious" plants, the flowers are predominantly pistillate (Peterson 1960, Peterson and Anhder 1960, Peterson and de Zeeux 1963, Peterson and Weigle 1958).
Pollination Requirements:
The need for insect pollination of cucumbers has been known for years. Before the turn of the century, honey bees were used to pollinate cucumbers grown under glass (McIntosh 1855, Root 1886, Pieters 1896, Hunn and Craig 1905, Corbett 1906, Lyon 1906). Later tests experimentally confirmed this need (Markov and Romanchuk 1959). The need for bees on fieldgrown cucumbers was also recognized (Jones and Rosa 1928*), and growers in localities where bees were scarce were advised to keep honey bees to insure fruit set (Beattie 1928, Seaton et al. 1936). More recent tests have verified earlier ones (Alex 1959, Beattie 1935, Connor and Martin 1 969a, b, 1970, Martin and Collison).28 Edgecombe (1946a, b) also reported that he used bees in the field for the transfer of pollen between cultivars for the production of hybrid cucumber seed. Numerous tests have shown that all present varieties of cucumber are inter-fertile, but the pollen must be transferred to the stigma by a pollinating agent, usually honey bees.
The exception is the previously mentioned parthenocarpic slicing cultivars. McCollum (1934) showed that the setting of fruit on these cultivars does not produce the inhibiting effect on plant growth comparable to that caused by fertilized fruit.
The relative time of anthesis in staminate and pistillate cucumber flower was determined by Atsmon et al. (1965). Connor (1969) found that the best time of day for effective cucumber pollination in Michigan was from 10 a.m. to 3 p.m. He also found that pollination was about equally effective whether the pollen was placed on one lobe of the stigma or on all the lobes. Seaton et al. (1936) also stated the stigma is receptive throughout the day but most receptive in the early morning and that several hundred pollen grains should reach the stigma for most effective pollination.
The pollination requirements of pickling cucumbers vary greatly with the variety used, the method of production, and the geographic area. Traditionally, pickling cucumbers have been produced on monoecious vines, planted at the rate of about 5,000 to 15,000 plants per acre. The first one or two fruits on each vine are handpicked when they reach the desired size, usually a few days after flowering. The vine continues to grow and set fruit, which is harvested in a succession of handpickings throughout the season, but the trend is toward machine harvesting (Stout et al. 1964).
During the 1960's the introduction of gynoecious cucumbers and the development of harvesting machines launched a new era in pickle production. The machine usually destroys the plant a's it harvests the fruit so there is only one harvest, commonly called a destructive harvest of the crop, although nondestructive or "multiple-pick" harvesting machines are also available. Yield somewhat comparable to a succession of handpickings is obtainable by planting 50,000 to 150,000 (that is, about 10 times as many) plants per acre and carrying out one machine harvest averaging one or two cucumbers per vine.
The gynoecious characteristic was an innovation designed to provide pistillate flowers in rapid succession. Staminate flowers are provided by blending in about 10 percent seed of a monoecious type. With adequate pollination, fruit forms quickly and, under favorable weather conditions, grows uniformly to an optimum size for machine harvesting. These revolutionary changes in pickling cucumber production have greatly increased the need for timely and adequate pollination because of the greater concentration of pistillate flowers and the need for more rapid, uniform fruit set necessary for a single machine harvest.
Pollinators:
Although cucumber flowers are attractive to bees, the crop is not considered a major source of nectar or pollen. Individual flowers produce relatively large amounts of nectar, but the number of flowers per acre is low relative to that of our major honey plants. Pellett (1947*) stated that in numerous localities cucumbers are of some importance to bees. Stephen (1970a) stated that bees get little pollen from cucumbers, and that pistillate and staminate flowers are about equally attractive.
Connor (1969) and Martin (1970) stated that even when honey bees visit staminate flowers, the primary objective is to collect nectar, and that cucumbers are visited for pollen largely when other sources of pollen are absent. Shemetkov (1960b) in Russia and Amaral et al. (1963) in Brazil reported that bees collected cucumber pollen heavily from 8 to 10 a.m. and nectar from 10 a.m. to noon. Bees work the blossoms later in the day in springtime or cooler climates than in summer or warmer climates. Nemirovich-Danchenko (1964) reported that nectar secretion was greatest 3 to 4 hours after the flower opens. Skrebtsova (1960) stated that pistillate flowers produce more nectar sugar than staminate ones. Amaral et al. (1963) concluded that bees show no preference for staminate over pistillate flowers. Connor and Martin (1969a, b) stated that in Michigan "native bees cannot and should not be relied upon as pollinators. The honey bee is the primary and only dependable pollinator of cucumbers." Tsyganov (1953) considered one bee equal in value to 11,000 thrips as pollinators of cocumbers. Skrebtsova (1964) stated that honey bees represented 84 to 96 percent of the insect pollinators on cucumbers. In many U.S. fields, they are the only pollinators present. Szabo and Smith (1970) reported that the leafcutter bee, Megachile pacifica, worked cucumbers in a greenhouse if the temperature remained at 30 deg C. Stephen (1970b) reported that honey bees failed to work effectively in plastic greenhouses, apparently because of the reduction in ultraviolet light.
Shemetkov (1957, 1960a) showed that a cucumber flower should be visited 8 to 10 times for satisfactory fruit set, but the number of seeds and weight of fruit increases up to 40 to 50 visits. Connor (1969) also found that as many as eight visits per flower were necessary for maximum set, and seed production was significantly greater with 20 or more visits than with 10 visits. Anderson (1941) stated that "nubbins," "balls," and "crooks" were the result of poor pollination resulting from too few bee visits per flower. Seaton (1937) reported that uniform fruits weighed 626 g and had 314 seeds, but constricted fruits weighed only half as much and had only 150 seeds.
Knysh (1958) removed and tested the viability of pollen from bees flying 250, 500, 750, and 1,000 m to the hive. He found that 38 percent of pollen grains taken from bees flying 250 m were viable but only 18 percent from bees flying 500 m. He found no viability in pollen grains that were carried greater distances. This indicates that the pollen grains exposed on the bee have a relatively short lifespan. Seyman et al. (1969) reported the importance of honey bees in cucumber production by obtaining increased fruit yield with increased exposure to bee activity. Shemetkov (1960a) calculated that one colony of bees was equal to 300 man-days in pollination of cucumbers.
In Michigan, one colony to 2 or 3 acres have been used to pollinate monoecious type cucumbers for handpicking. The flowers are attractive to bees, and even though the number of flowers per acre is low, bees continue to visit and pollinate the blossoms as they mature. The gynoecious hybrids grown for machine harvest present a different picture. Here the current Michigan recommendation is one colony to each 50,000 plants, or one to three colonies per acre (Martin 1970).
Connor and Martin (1970) using highly gynoecious cultivars showed that preventing the pollination of cucumber flowers for periods up to 11 days after the appearance of the first pistillate flowers resulted in higher yields of more uniform pickles. Unfortunately, this cannot yet be duplicated on a field basis because commercially developed gynoecious hybrids have not so far been able to maintain the gynoecious characteristic at a sufficiently high level to delay pollination. That is, present gynoecious hybrids produce some staminate flowers, so pollen is available as soon as pistillate flowers are produced. If fully gynoecious hybrids become available, growers may interplant a few rows of monoecious plants with gynoecious hybrids in such a way that staminate flowers appear later than pistillate flowers. Pollination could thus be delayed until the gynoecious plants attained better growth and capacity to produce a higher yield of more desirably shaped fruit. This points out that pollination studies coordinated with studies of other cultural practices including plant breeding may have broader application than has been fully appreciated to date.
Pollination Recommendations and Practices:
The literature leaves little doubt that insect pollination of cucumbers in the United States is essential to profitable production, and that honey bees are the primary pollinating agents. The question of the number of pollinators per unit area (acres or flowers) is not completely resolved. Recommendations have varied from "fields no farther than one- fourth mile from one or more swarms," to "a few stands [colonies] in or near the field," or from one colony per 10 acres to one strong colony per acre (Anonymous 1959; Alex 1959; Conner 1969; Conner and Martin 1969a, b; Davis and Hall 1958; Eckert 1959*; Martin 1970; Peto 1951; Seyman et al. 1969; Sims and Zahara 1968; Steinhauer 1970, 1971; Warren 1961, 1967). Hughes (1971) recommended 30 to 40 bees within a 30-foot circle. The University of Arizona (1970) recommended one bee per 100 flowers.
Recommendations should differ between monoecious, handpicked, low plant population, and gynoecious, single-machine-harvest, high plant population. Many of the recommendations that have been made are mere statements without supporting data, and, as might be expected, they vary considerably. The most thorough study of cucumber pollination has been made in Michigan (Connor 1969, Connor and Martin 1969a 1970, Martin and Collison 1970). It is of interest to note that although one strong colony per acre is recommended (Connor 1969, Connor and Martin 1969a, b) or "one colony per acre 2 or 3 might pay off" (Martin and Collison 1970), the data by Connor and Martin (1970) leave little doubt that production with three colonies per acre was significantly below their bee saturation (cage) population. In Michigan, more than three colonies per acre were required for maximum cucumber production when gynoecious hybrids were grown for machine harvest. Davis et al. (1970) indicated that honey bees were more effective if they were moved to the cucumber field after flowering had started. This was supported by Martin (1970) who showed that delayed pollination improved yield and fruit shape. Enzie (1934) stated that when bees are scarce it may be necessary to distribute hives among the larger plantings.
Hughes (1971) gave the most practical recommendation. He stated that, on a clear day walk into the cucumber field. If you cannot count 30 to 40 bees in a 30-foot diameter (within 15 feet) or cannot hear a very noticeable hum you probably need to bring in more bees. He generally recommended one colony per acre as essential, with two or more as desirable, or one bee per 100 flowers.
LITERATURE CITED:
ANONYMOUS.
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