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COLE CROPS ²³
Brassica oleracea L., family Cruciferae

A large number of crops belongs to the plant species B. oleracea, known collectively as cole crops. Considerable difference of opinion exists among authorities as to the exact classification of these crops into subspecies, varieties, and subvarieties. Also, types will intercross, and the subsequent generation adds to the confusion. Nieuwhof (1969) separated the species into the following classification of varieties and subvarieties:

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B. o., var. acephala DC. subvar. Iaciniata L. Curly Kale medullosa Thell. Marrow-stem kale millecapitata (Lev.) Thell. Thousand-head kale palmifolia DC. Tree kale plana Peterm. Smooth-leaf kale B. o., var. botrytis L. subvar. cauliflora DC. Cauliflower cymosa Lam. Sprouting (Italian) broccoli capitah L. f. alba DC. White cabbage f. rubra (L.) Thell. Red cabbage gemmifera DC. Brussels sprout gongylodes L. Kohlrabi sabauda L. Savoy cabbage

Nieuwhof (1969) considered collards and Portugal cabbage or tranchuda kales as transitional types between kales and cabbages.

In addition to the crops mentioned above, there are some other Brassicas for which little or no information exists on their pollination requirements. Because of the botanical relationship these requirements may be similar to known ones, although experience with some other crops has shown that even within a species the pollination requirements can be highly variable. These less well-known cruciferous crops grown primarily for their succulent leaves were listed by Bailey (1949*) as follows:

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B. carinata A. Br. Abyssinian mustard B. chinensis L. Pak-choi or Chinese cabbage B. fimbriata DC. Curled kitchen kale B. narinosa Bailey Broadbeaked mustard B. parachinensis Bailey Mock pak-choi B. pekinensis (Lour.) Rupr. Pe-tsai B. perviridis Bailey Tendergreen or spinach mustard B. ruvo Bailey Ruvo kale B. septiceps Bailey Seven-top or Italian kale

Cabbage and broccoli are the most important of the cole crops as indicated in table 10. Although cabbage is grown in more than half of the States on a total of 111,800 acres, Texas with 21,000; Florida with 17,600; New York with 11,200, and California with 9,700 acres account for more than half of the total production. The bulk of the broccoli, 30,600 acres of the 37,060 acres, and cauliflower, 17,900 of the 25,600 acres, produced in the United States came from California.

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TABLE 10.ÑAcreage and farm value of U.S. cole crops produced in 1970 __________________________________________________________ Crop Acreage harvested Dollar value (millions) __________________________________________________________ Broccoli, including sprouting broccoli 40,300 30 Brussels sprout 6,000 8 Cabbage 118,400 82 Cauliflower 23,900 22 Kale, including collards (1) (1) Kohlrabi (1) (1) __________________________________________________________ 1 Estimates discontinued.

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²³ For some closely related crops, see "Mustard," p.261; "Radish," p. 314; "Rape," p. 315; and "Turnip and Rutabaga," p. 365.

Plant:

The cole crops are large-leaved, succulent, and low-growing, 1 to 2 feet, until the inflorescence is formed then they may reach 2 l/2 to 7 feet in height. More are biennial than annual, although most cauliflowers are annual. Nieuwhof (1969) stated that when annual varieties are crossed with biennial ones in temperate zones, the F_l is annual, but at slightly higher temperatures the F₁ might become biennial.

The plants are usually grown in cool climates or in the cooler part of the year in warm climates, and they do best under conditions of relatively high humidity. The leaves, buds, or sprouts are eaten either fresh (salad), cooked (usually blanched), or processed (sauerkraut) (figs. 82 - 84). The seed-stem is of value only in the production of seed. Unless seed is produced, the plant is destroyed or abandoned after the succulent portion is harvested.

There are many cultivars of the different subspecies or "varieties" of B. oleracea (Thompson 1964).

[gfx]
FIGURE 82. - Brussels sprouts plant, showing sprouts at proper harvesting stage.
FIGURE 83. - Broccoli plant with head at proper stage for harvesting.
FIGURE 84. - Kohlrabi plants properly spaced and almost large enough to harvest.

Inflorescence:

After leafy growth ceases, as for example the completed growth of the head of the cabbage, or the sprouts of Brussels sprouts, the flowering stem elongates. It is characterized by numerous branches (mostly from a main stem), small leaves, and numerous bright yellow or occasionally white flowers. The flowers of all Cruciferae have four petals, l/2 to 1 inch long, that appear to form a cross, hence the name Cruciferae (cross bearing).

The flower opens during the morning, the anthers a few hours later, so the flower is slightly protogynous. There are six stamens, two generally shorter than the style and facing toward it but leaning away, and four erect stamens generally longer than the style and also facing it. There is a single capitate stigma terminating the style (fig. 85). In most cultivars, nectar is secreted by two nectaries located between the bases of the short stamens and the ovary. Nieuwhof (1969) stated that there are also two inactive nectaries outside the base of the two pairs of long stamens. The nectaries secrete freely, 0.1 cm³ nectar each 24 hours of the 3 days the flower is open (Pearson 1933). The flowers are highly attractive to pollinating insects for both nectar and pollen. When the seed-producing acreage is large, beekeepers nearby frequently harvest a crop of excellent honey.

The blossom forms a silique, incorrectly but commonly called a pod, 1 to 4 inches long. A silique is distinguished by the unfolding of its two outer "shells," leaving the 10 to 30 seeds enfolded in a membranous partition. A well-fruited cabbage plant may produce one-half pound of seed (Pearson 1932); a Brussels sprouts plant, one-quarter pound (Sciaroni et al. 1953). Yields of 1,300 to 1,700 pounds of seeds per acre of cabbage can be expected, depending upon soil, climate, and cultural practices (Schudel 1952), although, as shown below, the average production of seed per acre is much below this amount. One acre should produce enough seed to plant several hundred acres. Nieuwhof (1969) recommended 1 to 5 kg seed per ha, roughly 1 to 5 lb/acre, the amount depending upon the preciseness of the planting method. If the seeds are planted in a bed, then the young plants transplanted to the field, only 80 to 200 g of seed per acre of plants are needed.

The acreage and production of Brassica seeds in the United States is shown in table 11.

[gfx] FIGURE 85. - Longitudinal section of collard flower, x 6.

Pollination Requirements:

The cole crops require cross-pollination. Only in some varieties of cauliflower is seed setting partly brought about by selfing (Nieuwhof 1963, 1969). In general, the flower is self-sterile (Detjen 1927, Kakizaki 1922). Many plants are self-incompatible, and some are cross- incompatible (Attia and Munger 1960, Detjen 1927, Garcia 1954, Odland and Noll 1950). The pollen must be effectively transferred between plants that are cross-compatible. Pearson (1930, 1932) concluded that Brassica plants were 95 percent cross-pollinated.

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TABLE 11. - Acreage and production of Brassica seed crops in the United States _________________________________________________________ Harvested in- Production inÑ Kind of seed _____________________________________________ harvested 1969 1970 19711 1969 1970 19711 __________________________________ ____________________ Acres Thousand pounds Broccoli 51 97 120 56 78 85 Cabbage 358 526 664 200 351 402 Cauliflower 144 231 222 72 135 112 Kale 63 100 47 48 118 42 Kohlrabi 13 20 16 7 30 17 Mustard 379 193 204 444 288 220 Radish 1,880 1,348 1,347 1,641 1,389 1,157 Rutabaga 35 31 38 39 57 48 Turnip 591 481 422 856 758 482 __________________________________________________________ 1 Preliminary estimate

Moore and Anstey (1954) found up to 76 percent selfing in sprouting broccoli, but they did not indicate how much of the set was due to insect activity or if any of it resulted from the plants' own self-fertilization. Anstey (1954) found that 52 percent of sprouting broccoli plants were self-incompatible, 30 percent compatible, and 18 percent somewhere in between. But even with the compatible plants, the transfer of the pollen from anthers to stigma is necessary for best seed set.

Usually, plants grown in cages or otherwise isolated from pollinating agents set practically no seed even if the plants are occasionally shaken. Cross-pollinated cabbage flowers produced siliques with 10 or more seeds, but selfed flowers produced less than one seed each. Nieuwhof (1969) attributed this self-incompatibility to the fact that pollen on the stigma of the same plant germinates poorly, and he agreed with Knuth (1908*, pp. 74 - 128) that this incompatibility is strongest in freshly opened flowers. This illustrates Nature's abhorrence of selfing, accepting it reluctantly only as a last resort to preserve the species. The pollen must be transferred by an outside agent, and wind is not an important factor in its transfer, although Haskell (1943) and Jenkinson and Glynne-Jones (1953) stated that some pollen is moved by wind.

Many plants in the cole crops are male-sterile (East 1940, Nieuwhof 1961), and the use of this factor has been proposed in a hybrid seed production program (Attia and Munger 1950, Skrebtsova 1964). Sun (1937) showed that self-pollination of Brassica resulted in decreased yields in subsequent generations.

Increasing interest is developing in the production of hybrid seed. Legg and Souther (1968) showed that open-pollinated broccoli cultivars are unlikely to be used in a hybrid program, but Cole (1959) and Dickson (1970) reported finding a male-sterile mutant in sprouting broccoli, that might make hybrid seed production practical. Borchers (1968) showed that broccoli hybrids produced larger heads; 36 percent matured earlier and more uniformly than nonhybrids. Later, Borchers (1971) reported on the production of hybrid broccoli by using male-sterile plants with honey bees to do the crossing. Johnston (1964) demonstrated that hybrid vigor exists in the marrow-stem kale.

The most effective time for pollination during the 3 days the flower is open and the stigma is receptive has not been determined (Kakizaki 1925). More than one pollen-application period is probably necessary for fertilization of all the ovules in the ovary to produce a full silique.

Pollinators:

The construction of the flower is such that many kinds of insects can reach the pollen and nectar, including honey bees, wild bees, and flies. Blowflies have been used in cages where the pollination of only a few plants was involved (Faulkner 1962), but no practical method has been developed for their use in open-field pollination. Pearson (1932) considered bees of the family Andrenidae, Megachilidae, and Nomadidae [= Nomada spp. of Anthophoridae] more important than honey bees in the pollination of cabbage, but he did not say what the relative populations were, either on the plants or in the area. Sneep (1952) mentioned Bombus and Psithyrus but only incidentally.

Because cole crops flourish in cooler areas, the plants may come into bloom at temperatures below the minimum of about 55 degF at which honey bees fly. A few wild bees sometimes forage below this critical temperature, and if they are abundant, under such a climatic condition they could be important.

In general, the honey bee is the primary pollinator of cole crops (Hawthorn and Pollard 1964*, Jones and Rosa 1928 *, Nieuwhof 1969, United Nations 1961). It can be transported to the fields to be pollinated when desired. In the U.S.S.R., Skrebtsova (1964) reported that 84 to 94 percent of the pollinating agents on cabbage were honey bees. Radchenko (1966) reported that honey bees comprised 85 to 100 percent of the pollinators on cabbage, increased the seed crop by 300 percent over plants not freely visited, and that this visitation also considerably enhanced the seed quality. Sakharov (1958) showed that cabbage seeds from flowers receiving adequate bee visits were three times as large as those from flowers not visited by bees. Atkinson and Constable (1937) stated that the intense and repeated pollination that takes place within a cage when honey bees are enclosed results in more fruit set with more seeds per fruit than occurs in the open.

Pollination Recommendations and Practices:

Many publications on the production of cole crop seed give little or no consideration to the value of insect pollinators (Griffiths et al. 1946*), or these insects are considered only from the standpoint of varietal contamination (Baseman 1947 - 48, Knott 1949, Natl. Inst. Agr. Bot. 1942, Priestley 1954, Watts 1968).

The excellent United Nations (FAO) report (1961) stated that to insure good seed set of Brassicas, insect pollination of all the flowers is necessary. To accomplish this, they recommended placing colonies of bees near the larger fields but did not indicate how many colonies. Skirm (1971) said that bees were essential. Sakharov (1956) showed the following interesting relationship between a high density of bees and seed production and quality as follows:

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__________________________________________________________ Method of pollination used ________________________________________ Saturated pollination Free Self Explanation by bees pollination pollination __________________________________________________________ Average seed yield per plant 46.6 0.9 0.1 Weight of 1,000 seed................grams 4.8 2.0 (1) Germination.......percent 96 64 0 __________________________________________________________ 1 "Puny."

Eckert (I959*), without supporting data, recommended two colonies per acre of all vegetable seed. Odland and Noll (1950) stated that a colony of bees located by their plots increased the seed yields. Oldham (1948) stated that having "a few colonies of bees dotted around the field" was a distinct advantage. When more than 5 or 10 acres are involved, the chances are good that the local supply of wild bees is inadequate for maximum flower visitation and seed set. If this is likely to be the case, the grower should arrange for the placement of strong colonies of honey bees in or adjacent to his field during flowering.

The number of colonies needed will doubtless vary with their strength, the size of the field, and the competing plants that might lure the bees from his field. Under some conditions, two coloniesÑas recommended by Eckert (1959*)Ñmight be adequate. Under other conditions where the grower is striving for maximum seed production, twice as many or more may be needed. In any case, where seeds of cole crops are produced commercially, the grower should take steps to assure the presence of the maximum population of insect pollinators.

LITERATURE CITED:

ANSTEY, T. H.
1954. SELF-INCOMPATIBILITY IN GREEN SPROUTING BROCCOLI (BRASSICA OLERACEA L., VAR. ITALICA PLENCK) 1. ITS OCCURRENCE AND POSSIBLE USE IN A BREEDING PROGRAM. Canad. Jour. Agr. Sci. 34: 59-64.

ATKINSON W. T., and CONSTABLE, E. E.
1937 A HONEY BEE TECHNIQUE IN SEED PRODUCTION OF SELECTED CRUCIFEROUS PLANTS. Australasian Beekeeper 39(6): 183-185.

ATTIA M. S., and MONGER, H. M.
1950. SELF-INCOMPATIBILITY AND THE PRODUCTION OF HYBRID CABBAGE SEED. Amer. Soc. Hort. Sci. Proc. 56: 363 - 368.

BATEMAN A. J.
1947-48. CONTAMINATION OF SEED CROPS: 1. INSECT POLLINATION. Jour. Genet. 48: 257-275.

BORCHERS E. A.
1968 YIELD, UNIFORMITY OF HEADING AND SEASON OF MATURITY OF BROCCOLI INBREDS, HYBRIDS AND VARIETIES. Amer. Soc. Hort. Sci. Proc. 93: 352 - 355.

BORCHERS, E. A.
1971. HYBRID BROCCOLI SEED PRODUCTION UTILIZING THE M6 GENE FOR MALE STERILITY. Amer. Soc. Hort. Sci. Proc. 96: 542-543.

COLE, K.
1959. INHERITANCE OF MALE-STERILITY IN GREEN SPROUTING BROCCOLI. Canad. Jour. Genet. Cytol. 1: 203-207.

DETJEN, L. R.
1927. STERILITY IN THE COMMON CABBAGE (BRASSICA OLERACEA L.). Hort. Soc. N.Y. Mem. 3: 277-280.

DICKSON. M. H.
1970. A TEMPERATURE SENSITIVE MALE STERILE GENE IN BROCCOLI BRASSICA OLERACEA L., VAR. ITALICA. Amer. Soc. Hort. Sci. Proc. 95(1): 13-14

EAST, E. M.
1940. THE DISTRIBUTION OF SELF-STERILITY IN THE FLOWERING PLANTS. Amer. Phil. Soc. Proc. 82: 449-518.

FAULKNER, G. J.
1962. BLOWFLIES AS POLLINATORS OF BRASSICA CROPS. Com. Grower [England] 3457: 807-809.

GARCIA, G. M.
1954. A PRELIMINARY STUDY OF THE PRODUCTION OF CAULIFLOWER SEED. Philippine Jour. Agr. 19: 143-152.

HASKELL, G.
1943. SPATIAL ISOLATION OF SEED CROPS. Nature 152: 591-592.

JENKINSON, J. G., and GLYNNE-JONES, G. D.
1953. OBSERVATIONS ON THE POLLINATION OF OIL RAPE AND BROCCOLI. Bee World 34: 173 - 177.

JOHNSTON, T. D.
1964. INBREEDING AND HYBRID PRODUCTION IN MARROW-STEM KALE (BRASSICA OLERACEA L., VAR. ACEPHALA D.D.). Euphytica 13: 147-152.

KAKIZAKI, Y.
1922. SELF-STERILITY IN CHINESE CABBAGE. Jour. Hered. 13: 374 - 376.

______ 1925. A PRELIMINARY REPORT OF CROSSING EXPERIMENTS WITH CRUCIFEROUS PLANTS WITH SPECIAL REFERENCE TO SEXUAL COMPATIBILITY AND MATROCLINOUS HYBRIDS. Jap. Jour. Genet. 3(2): 49-77.

KNOTT, J. E.
1949. VEGETABLE GROWING. Ed. 4, 314 pp. Lea and Eebiger, Philadelphia.

LEGG, P. D., and SOOTHER, E. D.
1968. HETEROSIS IN INTERVARIETAL CROSSES IN BROCCOLI (BRASSICA OLERACEA VAR. ITALICA). Amer. Soc. Hort. Sci. Proc. 92: 432-437.

MOORE, J. F., and ANSTEY, T. H.
1954. A STUDY OF THE DEGREE OF NATURAL SELFING IN GREEN SPROUTING BROCCOLI (BRASSICA OLERACEAE L., VAR. ITALICA PLENCK) A NORMALLY CROSS-POLLINATED CROP. Amer. Soc. Hort. Sci. Proc. 63: 440 - 442.

NATIONAL INSTITUTE OF AGRICULTURAL BOTANY [ENGLAND].
1942. CROSS-FERTILIZATION IN BRASSICAS. Min. Agr. Jour. 49(2): 116-117.

NIEUWHOF, M.
1961. MALE STERILITY IN SOME COLE CROPS. Euphytica 10: 351-356.

NIEUWHOF, M.
1963. POLLINATION AND CONTAMINATION OF BRASSICA OLERACEA L. Euphytica 12: 17-26.

______ 1969. COLE CROPS. 353 pp. Leonard Hill, London.

ODLAND, M. L., and NOLL, C. J.
1950. THE UTILIZATION OF CROSS COMPATIBILITY AND SELF- INCOMPATIBILITY IN THE PRODUCTION OF F₁ HYBRID CABBAGE. Amer. Hort. Sci. Soc. Proc. 55, 391-402.

OLDHAM, C. H.
1948. BRASSICA CROPS AND ALLIED CRUCIFEROUS CROPS. 295 pp. Lockwood, London.

PEARSON, O. H.
1930. OBSERVATIONS ON THE TYPE OF STERILITY IN BRASSICA OLERACEA VAR. CAPITATA. Amer. Soc. Hort. Sci. Proc. 34 - 38.

______ 1932. BREEDING PLANTS OF THE CABBAGE GROUP. Calif. Agr. Expt. Sta. Bul. 532, 22 pp.

______ 1933. STUDY OF THE LIFE HISTORY OF BRASSICA OLERACEA. Bot. Gaz. 94: 534-550.

PRIESTLEY G.
1954. USE OF HONEY BEES AS POLLINATORS IN UNHEATED GLASSHOUSES. New Zeal. Jour. Sci. and Technol. 36(3): 232 - 236.

RADCHENKO, T. H.
1966. [ROLE OF HONEY BEES AS POLLINATORS IN INCREASING THE SEED CROP FROM CABBAGE AND RADISH.] Bdzhil'nytstvo 2: 72-74. [In Ukrainian.] AA-390/69.

SAKHAROV, M. K.
1956. [CABBAGE POLLINATION BY BEES.] In Krishchunas, I. V., and Gubin, A. F., eds. [Pollination of Agricultural Plants], pp. 180-181, Moskva, Gos. lzd-vo Sel-khoz. Lit-ry. [In Russian.]

SAKHAROV M. K.
1958. [POLLINATING ACTIVITY OF BEES ON SEED-BEARING PLANTS IN VEGETABLE CULTIVATION. ] Sad i Ogorod 96(7): 21 - 23. [In Russian.]

SCHUDEL, H. L.
1952. VEGETABLE SEED PRODUCTION IN OREGON. Oreg. Agr. Expt. Sta. Bul. 512, 79 pp.

SCIARONI, R. H., LANGE, W. H., JR., MINGES, P. A., and SNYDER, W. C.
1953. BRUSSEL SPROUTS PRODUCTION IN CALIFORNIA. Calif. Agr. Expt. Sta. Cir. 427, 16 pp.

SKIRM, G. W.
1971. [HYBRID CABBAGE.] Industrielle Obst- und Gemuseverwertung 56(5): 120 - 121. [In German, English abstract.]

SKREBSOVA, N.D.
1964. [USE OF THE POLLINATING ACTIVITY OF HONEYBEES FOR PRODUCING HYBRID VEGETABLE SEED. ] Trud. Nauch. -Issled. lnst. Pchelovod.: 223-245. [In Russian, English summary.]

SNEEP, J
1952. SELECTION AND BREEDING OF SOME BRASSICA PLANTS. Internatl. Hort. Cong. Rpt. 13: 422 - 426.

SUN, C. VON.
1937. EFFECTS OF SELF-POLLINATION IN RAPE. Jour. Amer. Soc. Agron. 29: 555 - 567.

THOMPSON, R. C.
1954. CAULIFLOWER AND BROCCOLI; VARIETIES AND CULTURE. U.S. Dept. Agr. Farmers' Bul. 1957, 16 pp.

UNITED NATIONS FOOD AND AGRICULTURE ORGANIZATION ( FAO)
1961. AGRICULTURAL AND HORTICULTURAL SEEDS. FAO Agro-studies 55, 531 pp.

WATTS, L. E.
1968. NATURAL CROSS-POLLINATION AND THE IDENTIFICATION OF HYBRIDS BETWEEN BOTANICAL VARIETIES OF BRASSICA OLERACEA L. Euphytica 17: 74-80.

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