THEORETICAL FRAMEWORK

Generalities of watermelon cultivation

Watermelon (citrullus lanatus) is a horticultural plant belonging to the cucurbitaceae family.

They are annual plants, with vegetative periods of 75 to 90 days, with abundant branching and
good vigor. It is a very refreshing food that provides very few calories to the body,
it also provides some vitamins A, B, C, and minerals.

Its growth habit is of trailing guides with tendrils at the ends, which in turn
they are covered with pubescence. Their fruits acquire different shapes and colors
depending on the variety to be cultivated. These can be spherical, ellipsoidal, or cylindrical,
red, yellow, or white pulp (Bolaños, 1998).

The family of cucurbits has created some confusion about its origin, but Casseres
(1976) states that the center of origin of the watermelon (citrullus lanatus) belongs to southern Africa.

Morphology of the watermelon

Plant

Watermelon is an annual, herbaceous plant, trailing or climbing in nature, from which its
fruits (MAGA, 1989).

Reticular system

The root system is very branched. The main root is deep and secondary roots are distributed.
superficially. After verifying that the introduction of resistance genes to fusariosis is
disease in some commercial varieties did not ensure normal production in soils
very contaminated. Additionally, this pattern offers resistance to Verticillium and tolerance to
Pythium and nematodes, giving great vigor to the plant and a powerful root system with roots
large superificadas (MAGA, 1989).

Stems

From creeping development. In a state of 5 to 8 well-developed leaves, the main stem emits the
secondary growths from the axils of the leaves. In the secondary growths, there
tertiaries begin and so on, so that the plant covers 4 to 5 meters
squares. These are green herbaceous stems covered with hairiness that develop
in a creeping manner, able to climb due to the presence of bifid or trifid tendrils, and they reach
a length of 4 to 6 meters (Reche, 1998).

Leaves

Peciolated, pinnate-parted, divided into 3 to 5 lobes, which in turn divide into segments
rounded, featuring deep grooves that do not reach the main nerve. The beam is soft
to the touch and the reverse very rough and with very pronounced nervations. The main nerve branches out
in secondary nerves that subdivide to direct towards the last segments of the leaf,
imitating the palm of the hand (Reche, 1998).

Flowers

Yellow in color, solitary, pedunculated and axillary, attracting insects by its color, aroma and
nectar (entomogamous flowers), so that pollination is entomophilous. The corolla, with symmetry
regular or actinomorphic, is formed by 5 petals joined at their base. The calyx is made up of
free sepals (dialysepal or corisephal) of green color. There are two types of flowers: male or
staminate and pistillate, with both sexes coexisting on the same plant, but in
distinct flowers (unisexual flowers). Male flowers have 8 stamens that form 4
groups of soldiers by their filaments (Reche, 1998).

Female flowers have rudimentary stamens and a woolly, ovoid inferior ovary that
it resembles in its first stage a watermelon the size of an olive pit (incipient fruit),
so it is easy to differentiate between male and female flowers. The latter appear
both in the main shoot and in the secondary and tertiary ones, with the first flower in the axil of
the seventh to the eleventh leaf of the main shoot. There is a correlation between the number of
germinated pollen tubes and fruit size (Reche, 1998).

Fruit

It corresponds to a globose or oblong berry in pepo, formed by 3 fused carpels with

adhered receptacle, which gives rise to the pericarp. The ovary shows central placentation, with
numerous eggs that will give rise to the seeds. Their weight ranges from 2 to 20 kilograms.
The color of the bark is variable, it can appear uniform (dark green, light green, or
yellow) or with stripes of yellowish, grayish, or light green color on various backgrounds
green tones. The flesh also presents different colors (red, pink, or yellow) or
show variable sizes and colors (black, brown or white), depending on the cultivar (Reche,
1998).

Varieties of watermelon

According to Bolaños (1998), there are two types of watermelon recognized: the American ones, with long, large fruits.

and with thick skin and the Japanese varieties of round, small fruits with thin skin.
In the group of American varieties, 'Charleston Gray' stands out, which was widely cultivated in
In Bolivia, the Japanese variety 'Crismón Sweet' is the variety that is currently being cultivated.

Ecology of the crop

The cultivation of watermelon adapts very well to altitudes between 0 and 900 meters above sea level, although
its development is best obtained when cultivated between 25 to 150 meters above sea level. The best time for

Sowing takes place in the months with the lowest relative humidity, being outside of the season.
rainy, October to January, since the crop does not tolerate waterlogging, as it is susceptible to
fungal diseases (Pérez, 1990).

Climate requirements

The cultivation of watermelon, unlike melon, is less demanding in temperature. Being the
more demanding cultivars than the normal ones. The optimal temperature required for the crop is
understood between 25º to 28º C for its development stage, and for its flowering it requires a
optimal temperature of 18º to 20º C. During the flowering and ripening of the fruit requires 23º to 28º
C. When temperatures differ between day and night in a range of 20º to 30º C, they cause
physiological disorders in plants. In some cases, the neck, stems, and pollen open up.
produced is not viable, watermelon is a warm climate crop and does not tolerate frost, relative humidity
The optimal humidity for watermelon is between 60% and 80% (Infoagro, 2003).

Soil requirement
The cultivation of watermelon is not very demanding in soil quality, although it is better to plant it in soils
flat, deep, drained, rich in organic matter (Infoagro, 2003). It adapts very well to
soils with clay-loam texture but prefers soils with sandy-loam texture, with a pH
understood between 6 to 7, does not tolerate salinity (Ruano and Trescastro, 1990).

Nutritional requirements of the crop

Bolaños (1998) recommends applying 100 kg N/ha, 20 kg/ha of P2O5, and 30 kg/ha of K2O. Therefore
assuming that the volume of fertilizer depends on the planting density and the level of fertility
from the ground. Miguel (1997).

Bertsch-Hernández and Ramírez Castrillo (1997) evaluated the nutrient absorption curves.
in watermelon (Citrullus lanatus), finding that to obtain a production of 44 tons
Watermelon metrics per hectare consume from the soil 108 kg Ca, 89 kg K, 57 kg N, 23 kg Mg and
8 kg of P; however, the elements that are most consumed in the fruit are: potassium 56% and phosphorus
50%. In watermelon, the moments of maximum absorption coincide with the release of guides and the start of
flowering, 33-40 days after sowing (dds) and after maximum flowering and start of
filling of fruits (45-50 dds). 60% of N is consumed before 40 dds; P undergoes a
more gradual absorption and K is consumed later than in melon (at 45 dds only has been)
consumed 35%.

Cultural practices for watermelon cultivation

Land preparation

The land is prepared in advance of planting using deep plowing and then
two cross harrow passes. Depending on the type of soil, the planting density varies
to differentiate, but usually it is planted from 1.8 to 2.0 m between rows and 0.90 to 1.25 m between
positions, placing 2 to 3 plants, 0.45 to 0.5 kg/ha of seed is used (Pérez, 1990).

Growing season
Watermelon seeds germinate better when the soil temperature is at a minimum of 15º C.
and the optimal at 25º C. For the vegetative phase, the optimal relative humidity is between 60% and the
80%, being a very determining factor for its flowering (Infoagro, 2003).

The activities for planting watermelon are variable, depending on the location of the place, there are
some areas that can be sown with residual moisture in the months of November to
December, then irrigation areas, which can be by gravity or by drip, which is carried out during
the dry season months, which span from December to April, and the watermelon that is sown during
the rainy season that lasts from May to September (MAGA, 1989).

Get lost

This operation is performed optionally, according to the chosen framework, as they have been appreciated.

better yields in the production of pruned watermelons. Its purpose is to control the
way in which the plant develops, removing main shoots, to hasten the sprouting and
the growth of the side shoots. It consists of removing the main shoot when it has between 5
6 leaves, allowing to develop 4 to 5 secondary shoots that emerge from their axils.
giving a rounder shape to the plant (Reche, 1998).

Pollination

Normally, if the environmental conditions are favorable, the use of bees is advisable.
(Aphis melífera) as pollinator insects, since the use of hormones yields results
they are unpredictable (e.g. fruit malformation, etc.), due to the many factors of
cultivation and environmental factors that influence hormonal action. The number of hives may vary
from 2 to 4 per hectare, and it can even be higher, depending on the planting framework, the condition
vegetative of the crop and the climate of the planting location. Associations are sought in the
that the bloomings of the pollinator and the pollinated coincide in a ratio of 30-40%
pollinator + 60–70% pollinated or 25–33% pollinator + 67–75% pollinated
(Reche, 1998).

Collection
Generally, this operation is carried out by specialists, guided by the following
external characteristics (Reche, 1998):

a. The peduncle of the fruit must be completely dry, or the first leaf located
above the fruit is wilted.
b. When tapping the fruit with your fingers, it should produce a dull sound.
c. When squeezing the fruit in the hands, a clear sound can be heard as if it were cracking.
internally.
d. When scratching the skin with the nails, it separates easily.
The fruit's bed takes on an ivory yellow color.
The waxy layer (bloom) that is on the skin of the fruit has disappeared.
g. Loss of 35–40% of its maximum weight.

Pests in watermelon cultivation

According to Casseres (1976), a large group of insects cause considerable damage to the crop
the watermelon. The economically important ones are: whitefly (Bemisia tabaci), the aphids of the
genera Aphis and Myzus, nematodes of the genus Meloidogyne. For their control, it is necessary
implement a plant health program with preventive methods and appropriate cultural techniques
to avoid creating resistance to pesticides.

Red spider: Tetranychus urticae, (Acarina: Tetranychidae).

This pest causes considerable damage to the crop; it generally develops on the underside of the
leaves causing discolorations, such as yellowish spots that can be seen on them
first symptoms. When their population increases, the desiccation and defoliation of the
crop, its most severe attacks occur in the early phenological stages, the temperatures
high temperatures and low relative humidity favor the development of the pest (Infoagro, 2003).

Whitefly: Bemisia tabaci.

The young parts of the plants are sensitive to being colonized by the adults, who in turn
they lay eggs on the underside of the leaves, in this way the first larvae emerge, which go through
through three larval stages and one pupal stage. The direct damage is caused by the adults and the larvae.
feeding on the sap of the leaves, producing a yellowing color and
weakening in the plant. Another significant damage is the transmission of viruses from
yellowing in cucurbits caused by the species Trialeurodes vaporariorum, while
Both Bemisia tabaci is potentially a transmitter of a greater number of viruses in crops.
horticultural and is currently acting as a transmitter of the tomato yellow curl virus
(TYLCV), known as the 'spoon virus' (Infoagro, 2003).

Aphid: Aphis gossypii, (Sulzer) (Homoptera: Aphidae).

These species of aphids are the most common and abundant. They exhibit polymorphism, with females
winged and wingless forms of viviparous reproduction. The wingless forms of the first exhibit black siphons.
in the green or yellowish body, while those of Myzus spp. are completely colored
green, although at times they are found brown or pink. These insects form colonies and
They are distributed in clusters, which generally disperse in the summer through their females.
aladas (Infoagro, 2003).

Leaf miners: Liriomyza spp., (Burgess) (Diptera: Agromyzidae).

The adult females lay eggs inside the tissue of the younger leaves, usually on the upper surface,
where the larvae hatch and they in turn feed on the parenchymal tissue, causing
galleries are visible cases and these are sometimes different, although not always distinguishable.
Once the larval development is completed, they leave the leaves to pupate, on the ground or on the leaves to
subsequently giving way to adults (Infoagro, 2003).

Diseases in watermelon cultivation

Cucurbits are affected by a variety of diseases caused by fungi.

phytopathogens such as Fusarium sp., downy mildews, vascular and non-vascular diseases, which cause
damage of economic consideration. To avoid them, crop rotation must be done, to plant
resistant varieties and use preventive and curative fungicides (Infoagro, 2003).

Ash
This disease is caused by the fungus Sphaerotheca fuliginea, and it manifests through
dusty white spots on the surface of the leaves (top and underside), affects the stems
and petioles and even to fruits in very strong attacks. The affected leaves and stems show a
yellowish color and they dry completely (Infagro 2003).

Wilting due to Fusarium, Fusarium spp.

In watermelon, it produces a vascular disease that penetrates the soil through the roots, which ...
quickly extends through the xylem, producing a brown color in the conducting vessels
from the roots to the leaf area. The plant's growth stops, the fruits ripen
prematurely and the plant may end up dying (Miguel, 1997).

Verticillium dahliae Kleb

It also causes wilting in the plant like Fusarium spp. This disease is found
more frequent at low temperatures. Both Fusarium spp and Verticillium are the most
are geographically distributed. This fungus is extraordinarily polyphagous, being able to
develop on hundreds of guests. It causes the plant to wilt and
yellowing of the leaves, also produces internervial necrosis in the leaves, this progresses from
upward toward the plant (Miguel, 1997).

Pseudomonas solanacearum

This is an important bacterial disease, especially in the tropics. Pseudomonas is also

vascular and it evolves in the plant very quickly. Initially, wilting manifests.
unilateral leaves and appearance on the stem, roots, and greatly affects the fruits giving them
an aspect of freckles (Monera and Olmos, 2003).

Marketing of watermelon

The marketing of small-medium sized varieties is done in boxes with 4 to 8.

fruits. In the large-sized varieties, marketing is done in bulk on pallets. The
future perspectives regarding marketing lie in the size of the fruit, since it
has the problem of being too large for the family sizes of society, which
are decreasing considerably. That is why in the future the trend will probably
it would lead to small-sized fruits (less than 2 kg). It will probably also increase the quota of
market for seedless cultivars, and there is a trend towards diversification of types and the development of
more uniform cultivars in terms of organoleptic characteristics (Reche, 1998).

Variety of study

Charleston Gray variety: It has open pollination, with a life cycle of 80 to 90 days.
tolerant to anthracnose and moderately tolerant to Fusarium. It adapts to arid and tropical climates,
The fruits are elongated, with rounded ends; the epidermis is grayish, with a reticulated pattern.
green end; the flesh is bright red, sweet and tasty, and the seeds are dark. The
The weight fluctuates between 28 to 35 pounds and is resistant to transport (INIFAP 2006)

Crimson Sweet variety: It features elongated fruits of medium sizes and weights, the color of the
The skin is light green, with dark green veins and the pulp is red with few seeds.
This variety is in high demand in the North American market due to its size characteristics.
of the fruit. (INIFAP 2006)