Chapter 6: Common Vegetables for Seed and Fruit


Chapter 6: Common Vegetables for Seed and Fruit


WATERMELON (AND STOCKMELON, PIE MELON, OR CITRON MELON)
Citrullus lanatus (Thunb.) Mansf., family Cucurbitaceae

The watermelon is our largest edible fruit. When ripe, the sweet juicy pulp is eaten fresh, and the rind is sometimes preserved (Dupree et al. 1953). The pulp of the relatively rare stockmelon, pie melon, or citron melon is used in pies. This melon, indistinguishable externally from the watermelon, can only be opened with great difficulty. It is inedible in the raw state.

Watermelons usually range in size from about 10 to 50 pounds, depending upon the cultivar and area where it is grown. Isolated growers in southwest Arkansas and northeast Texas specialize in jumbo sizes that weigh in excess of 100 pounds (Kennerly 1960); one was produced near Hope, Ark., that weighed 195 pounds.

Watermelons are grown in almost every State, but roughly two- thirds of the 276,900 acres grown in 1969 were in four States: Texas (70,000), Florida (53,500), Georgia (37,500), and South Carolina (24,000 acres). The value of the 1969 crop was $54 million. Production per acre ranged from 3.35 tons in Texas to 7.8 tons in California.

In recent years, triploid or "seedless" and hybrid watermelons have been produced in limited quantities (Kihara l95l, Mohr et al. 1956, Watts 1962). They have not attained prominence, compared to regular open-pollinated watermelons.

Plant:

The watermelon plant is a slender, sprawling, slightly hairy, monoecious annual. The stems or runners may extend 1l/2 to 5 yards. The deeply lobed leaves are 1 to 6 inches wide and 2 to 10 inches long, on 1- to 5-inch stems. The fruit varies according to the cultivar; the shape from oblong to round; the rind, from light green to dark green or mottled light and dark green; the flesh, from red to yellow, rarely to light green or white; the seeds, from white to yellow, brown, black or reddish black; and the shipping quality, from a tender easily broken or bruised skin to a firm and tough rind (Whitaker and Davis 1962*). Spivey (1960) listed three types of melons - regular, icebox, and seedless. Juice from the red part of a watermelon contains 8 to 10 percent solids, of which 20 to 50 percent is sucrose. An edible sirup can be made from the juice (Webster and Romshe 1951).

The fruit and the vine are susceptible to frost. The plant is started from seed in rows about 6 feet apart, the plants 1 to 6 feet apart in the row. From one to four marketable melons are harvested per plant.

Because of the care necessary and the time consumed in harvesting the perishable ripe melons, vast acreages are seldom grown by individuals. Fields of 20 to 50 acres are most prevalent although fields of 200 to 300 acres are not rare.

Inflorescence:

All cultivars of watermelons and citron melons bear staminate and pistillate flowers, except for a few that bear hermaphrodite flowers instead of pistillate ones (Rosa 1925, Goff 1937). The pale yellow to greenish flowers, about 1 inch in diameter, are much less conspicuous than those of several other genera of the family Cucurbitaceae. The flowers are borne singly in the axils, the pistillate or hermaphroditic one occurring in every seventh axil, the staminate ones occupying the intervening axils. The pews of the flower are united in a tiny tube, just as in the cucumber, and are deeply five-lobed, with three stamens around a short blunt style and a three-lobed stigma tightly crowded into the corolla tube. Nectar is secreted in the base of the corolla. All staminate and most of the pistillate flowers shed, and there does not seem to be a definite cycle to fruit setting. The fruit sets more or less irregularly throughout the season, or at least as long as the plants are growing vigorously.

The flowers open 1 to 2 hours after sunrise. The pistillate flower and the staminate flower just below it open the same day. The anthers have dehisced when the corolla expands, but the pollen remains on the anthers in sticky masses. The stigma is receptive throughout the day although most pollination takes place in the forenoon. In the afternoon, the flower closes never to reopen, whether pollination has or has not taken place (Jones and Rosa 1928*).

The flowers are attractive to bees for both the nectar and the pollen. The number of blossoms per square yard is never great compared to the blossoms of clover, alfalfa, and most fruit.

Pollination Requirements:

Watermelon pollen is not windblown (Porter 1931). The flowers are almost exclusively insect pollinated. There is no self-sterility so far as the plant is concerned. Pollination is equally effective if the pollen is brought from the adjacent staminate flower on the same branch or from another plant. At least 1,000 grains must be evenly deposited on the three lobes of the stigma if a uniform melon is to result (Adlerz 1966). The watermelon style has no styler canal, but most pollen grains grow directly downward from their point of deposit. Mann (1943) found that 21 to 22 percent of the pollen tubes show some lateral movement, but if an insufficient amount of pollen is deposited on one lobe of the stigma, an asymmetrical melon results. It may be lopsided or it may be smaller on one end than the other. Watermelons are severely graded according to symmetry.

Adlerz (1966) studied the relationship between time of day and set of flowers visited by six or more bees or pollinated by hand. He (and Parris 1949) found that the highest percentage of fruit set resulted from deposition of pollen on the stigma between 9 and 10 a.m. Porter (1933) and Poole and Porter (1933) concluded that fertilization after hand pollination was most likely between 7 and 11 a.m. The morning activity of the bees is of greatest concern in watermelon pollination. Goff (1937) reported that bees, in Florida melon fields, reached their greatest abundance around 8:30 to 9 a.m.

Adlerz (1966) also studied the relationship between fruit set and length of the ovary at time of pollination. He found that the longer the ovary the better the chance that a fruit would set. Only 22 percent of 103 ovaries 20 mm or less in length set fruit, whereas 67 percent of those over 28 mm set fruit. Cunningham (1939) concluded that both the physiological condition of the plant and the number of fruit already set on it seem to determine the number of pistillate flowers that set later. Hibbard (1939) showed the value of thinning by stating that most growers fail to harvest one melon per plant. Also, the presence of a cull will inhibit setting of normal fruit for several weeks. It therefore appears that number of bee visitors (eight or more), time of bee visits (6 to 10 a.m.), length of ovary at time of pollination (28 mm or longer), plant vigor, and number of melons already set on the vine, all contribute to the greatest percentage of fruit set.

Pollinators:

The recognition of the need for insect pollination of watermelons is not new. Newell (1903) quoted the following statement made by P. J. Berckmans in August 1877, "Our watermelon growers would find their occupation gone if honey bees and other (pollinating) insects were out of existence."

Porter (1933) concluded that watermelon pollination is almost entirely by insects. Goff (1937, 1947) collected different species of bees, Apis mellifera L., Halictus spp. Augochlorella gratiosa Smith, Agapostemon splendens Lepeletier, and Augochloropsis caerulea Ashmead (listed in the order of their abundance) and concluded that the honey bee was by far the most abundant. Rosa (1925) and Jones and Rosa (1928*) concluded that pollination was chiefly by bees. Purseglove (1968*) stated that the watermelon is pollinated by insects, particularly honey bees. Brewer (1974) also concluded that honey bees were adequate, but he believed that increasing the bee population did not improve melon weight or seed yield. Adlerz (1966) showed that honey bees are highly effective as pollinators if they are sufficiently abundant in the field. Smith (1933) concluded that the lack of sufficient honey bees to pollinate early watermelon blooms in the Big Bend area of Oklahoma cost the growers in that district thousands of dollars annually.

Honey bee visits to melon flowers are primarily in the morning from 1 to 2 hours after sunrise when the flower first opens. Visitation continues until about mid-afternoon, depending on temperature and other weather conditions. The peak period of activity is usually mid-morning. The bees visit the flowers for both nectar and pollen, but because of the scarcity of blooms they never store surplus amounts of either. Adlerz (1966) recorded the average time that honey bees spend on melon flowers: 5.7 seconds per female flower in 1959, and 8.0 seconds per female and 5.7 per male flower in 1960. He considered duration of the visit relatively unimportant as the bee seemed to move about but little after it began to collect the food from the flower. This type of visitation indicates that the honey bee is obtaining a substantial amount of food from one blossom. For most efficient pollination, the bee should be forced to "shop around" among numerous flowers to obtain its load of food.

The effect of number of visits to the flower is of great importance to production of the mature melon. Adlerz (1966) learned that fruit set and yield after eight or more bee visits to the flower was superior to four or fewer visits. Only two of 64 flowers receiving one bee visit and one of 72 receiving two bee visits developed fruit and these fruits were small, badly shaped, and unmarketable. No melons set on flowers caged to exclude bees. Fruit set after eight bee visits was significantly better than after two or four visits. He considered eight visits to be the minimum for adequate pollination. Because bees do not uniformly visit all flowers, many flowers will receive more than eight visits if all are to receive this number.

Adlerz (1966) concluded that distribution of pollen over the stigmatic surface depended more upon multiple visits than upon length of visits or movement of the bee on the flower. Mann (1943) showed that if adequate amounts of pollen are not deposited on every stigma lobe, the melon will be misshapen - the most common reason for rejecting melons from the number one or highest priced category.

Pollination Recommendations and Practices:

Peto (1951) reported that one to five hives of honey bees were used per acre on cucumbers, cantaloupes, and watermelons grown for seed in relatively small fields. Wadlow (1970) used one colony per five acres of watermelons, the colonies placed in small groups in the field. Breece (1962) recommended one colony per acre, the bees on at least two sides of a 40-acre field. Adlerz (1966) made his studies in fields with one colony per acre and concluded that he had more visitors than necessary to provide eight visits per flower. Eckert (1959*) stated that one colony for each 2 acres may be enough. The Arizona Agricultural Experiment Station and Cooperative Extension Service (1970) recommended a bee population that will provide one bee for each 100 flowers in all parts of the field. This recommendation seems to be the best considering the influence of various environmental factors on bee activity.

LITERATURE CITED:

ALDERZ, W. C.
1966 HONEY BEE VISIT NUMBERS AND WATERMELON POLLINATION. Jour. Econ. Ent. 59: 28-30.

ARIZONA AGRICULTURAL EXPERIMENT STATION and COOPERATIVE EXTENSION SERVICE.
1970. MELONS AND CUCUMBERS NEED BEES. Ariz. Agr. Expt. Sta. and Coop. Ext. Serv. Folder 90, leaflet.

BREECE. J. R.
1962. WATERMELONS. SAMPLE COSTS AND PRODUCTION. Calif. Agr. Ext. Serv. (Imperial County) Cost Data Sheet 10, leaflet.

BREWER. J. W.
1974. POLLINATION REQUIREMENTS FOR WATERMELON SEED PRODUCTION. Jour Apic. Res. 13: 207-212.

CUNNINGHAM, c. B.
1939. FRUIT SETTING OF WATERMELONS. Amer. Soc. Hort. SC;. Proc. 37: 811-814.

DUPREE, w. E., WOODRUFF, J. G., and SIEWERT, s.
1953. WATERMELON RINDS IN FOOD PRODUCTS. Ga. Agr. Expt. stat Bul. 285, 30 pp.

GOFF, C . C.
1937. IMPORTANCE OF BEES IN THE PRODUCTION OF WATERMELONS. Fla. Ent. 20(2): 30-31.

______ 1947. BEES AND WATERMELON GROWERS. Fla. Grower 56(1): 13, 27.

HIBBARD, A. D.
1939. FRUIT THINNING THE WATERMELON. Amer. soc. Hort. sci. Proc. 37: 825-826.

KENNERLY, A. B.
1960. BEES HELP GROW JUMBO WATERMELON. Gleanings Bee Cult. 88: 406-407.

KIHARA, H.
1951. TRIPLOID WATERMELONS. Amer. Soc. Hort. sci. Proc. 58: 217-230.

MANN, L. K.
1943. FRUIT SHAPE OF WATERMELONS AS AFFECTED BY PLACEMENT OF POLLEN ON THE STIGMA. Bot. Gaz. 105: 257-262.

MOHR, H. C., BLACKHURST, H. T., and JENSEN, E. R.
1956. F1 HYBRID WATERMELONS FROM OPEN-POLLINATED SEED BY USE OF A GENETIC MARKER. Amer. Soc. Hort. Sci. Proc. 65: 399-404.

NEWELL, W.
1903. THE RELATION OF BEES TO FRUIT GROWING. Ga. State Hort. Soc. Proc. 27: 58-63.

PARRIS, G. K.
1949. WATERMELON BREEDING. Econ. Bot. 3: 193-212.

PETO, H. B.
1951. POLLINATION OF CUCUMBERS, WATERMELONS AND CANTALOUPES. In lowa State Apiarist Rpt., 1950, pp. 79-87.

POOLE, C. F., and PORTER, D. R.
1933. POLLEN GERMINATION AND DEVELOPMENT IN WATERMELON. Amer. Soc. Hort. Sci. Proc. 30: 526-530.

PORTER D. R.
1931. SOME EFFECTS OF INBREEDING WATERMELONS. Amer. Soc. Hort. Sci. Proc. 27th Ann. Mtg. Dec. 29-30, 1930: 554-559.

______ 1933. WATERMELON BREEDING. Hilgardia 7(15): 585-624.

ROSA, J. T.
1925. POLLINATION AND FRUITING HABIT OF THE WATERMELON. Amer. Soc. Hort. Sci. Proc. 22: 331-333.

SMITH, B.
1933. HONEYBEES PRODUCE PROFITS FOR MELON GROWERS. Amer. Bee Jour. 73: 349.

SPIVEY, C. D.
1960. GROWING WATERMELONS. Ga. Agr. Ext. Serv. Cir. (leaflet) 466.

WADLOW, R. V.
1970. POLLINATION OF CROPS IN FLORIDA. In The Indispensable Pollinators, Ark. Agr. Ext. Serv. Misc. Pub. 127, pp. 61-63.

WATTS, V. M.
1962. A MARKED MALE-STERILE MUTANT IN WATERMELON. Amer. Soc. Hort. Sci. Proc. 81: 498-505.

WEBSTER, J. E., and ROMSHE, F. A.
1951. WATERMELON SIRUP: ITS COMPOSITION AND COMPOSITION OF THE JUICE FROM WHICH IT WAS MADE. Amer. Soc. Hort. Sci. Proc. 57: 302-304.


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