Estructuras refractivas del ojo

Five genera of interest because of the fruit: Psidium, Eugenia, Syzygium, Myrciaria and Feijoa. All usually have simple opposite leaves and bisexual fl owers, with four or fi ve calyx lobes, that are separated or united at the base.

Flowers have four or fi ve petals and numerous stamens. The ovary is usually inferior and has one to three or more cells. The fruit is a berry or capsule, or rarely a drupe or nut-like. It has few to many seeds.

Psidium

This genus is composed of approximately 150 species of evergreen trees and shrubs in the American tropics. A good taxonomic classifi cation of this genus is lacking. P. guajava L. is by far the most widely known and distributed species. Common names include guava, guajaba, gujaba, goyavier and jambu bat (Malaysian). P. friedrichsthalianum (O. Berg) Medenza is known as the Costa Rican jelly guava. It is a shrub or small tree with square branchlets and glossy leaves above and pubescent below. The fruit is small (2.5–3.0 cm),

5

sulfur-yellow and very acid. The plant has some diffi culty fruiting at sea level, but does well at higher elevations. It is cultivated as a backyard plant in Costa Rica.

P. guineense Swartz. (P. araça Raddi; P. molle Bertol), the Brazilian jelly guava, has highly acid yellow fruit of 2.5–3 cm diameter when ripe. It bears heavily at sea level and is quite tolerant to lower temperatures. P. littorale Raddi var.

longipes (O. Berg) Fosb. and P. littorale Raddi var. littorale were formerly known as P. cattleianum Sab. and P. cattleianum var. lucidum (Degner) Fosb., respectively.

The variety longipes is popularly known as the purple strawberry guava or Cattley guava, while var. littorale is known as the yellow strawberry guava or yellow Cattley, and they are vegetatively indistinguishable. The fruit of both varieties are about 1.5–2.5 cm in diameter and seedy. They are somewhat sub-acid, but with a pleasant aroma.

Eugenia

This genus comprises a large and heterogeneous group of evergreen trees and shrubs of the American tropics and the Old World. Most of the Asian species were transferred to the genus Syzygium when Eugenia was revised, thus making Eugenia a smaller group. The Eugenia diff er from Syzygium in having cotyledons that are usually united; the seed-coat is smooth and free from the pericarp, and the infl orescence is generally a raceme of pedicelled fl owers.

E. brasiliensis Lam (E. dombeyi [K. Spreng.] Skeels) is commonly called the Brazilian cherry, and produces cherry-size, dark-red to black fruit on trees up to 15 m tall. E. unifl ora L. (E. michelii Lam), commonly called Surinam cherry or pitanga, is a native of Brazil. It has an eight-carpellate (furrowed) fruit, which is red to purple when fully ripe and spicy and acid. It is frequently used as an ornamental.

Syzygium (Jambosa DC)

This genus contains 400–500 species, mostly from south-east Asia. It is described in full in Chapter 11.

Myrciaria

This genus contains some very interesting species such as M. caulifl ora and M. jaboticaba, which are closely related species called jaboticabas. The trees and shrubs have good-tasting fruit that are borne on old stems and branches (caulifl ory). Another important species is M. dubia (HBK) Mc Vaugh or M.

paraensis O. Berg, the camu camu. This fruit has a high vitamin C content (2780 mg/100 g) and is exported from Peru, Bolivia and Brazil as a direct source of vitamin C, normally as fruit pulp. For several months of the year the plant grows wild on lands that are fl ooded by rivers in the Amazon valley, but it can also grow under normal soil conditions with irrigation.

Feijoa

This genus is represented by two evergreen species in South America. F.

sellowiana O. Berg is well known as feijoa or pineapple guava and is found wild in southern Brazil, Paraguay, Uruguay and northern Australia. It grows well in parts of California under dry subtropical climates.

Area of origin and distribution

The most well-known species in this family, guava (P. guajava L.), is native to the American tropics. The extent of its dissemination in the pre-Columbian period is obscure. The English name ‘guava’ probably came from the Haitian name guajaba. The Spanish explorers took guava to the Philippines, while the Portuguese disseminated it from the Philippines to India. It spreads easily and rapidly throughout the tropics because of an abundance of seeds with long viability. The species has become naturalized to the extent that people in diff erent countries consider guava to be indigenous to their own region. It is now also grown in the subtropics. The hardiness of guava has made it an invasive pest, especially in pasture lands.

ECOLOGY Soil

Guava is adapted to a wide variety of soil types. Trees will thrive on shallow, infertile soils, although growth and production are poor (Duarte, 1997). It responds well to soils with good drainage and high organic matter, with a pH range of 5–7. Cultivation in soils with a pH of less than 5 or higher than 7 will usually lead to symptoms of zinc and iron (Fe) defi ciency, respectively. Guava is fairly tolerant to salt. The threshold for seedling growth is 1.2 dS/m, and at 14 dS/m seedling survival is 25% after 50 days (Tavora et al., 2001). Fruit size and ascorbic acid decrease with increasing salinity to 5.0 dS/m.

Climate

Rainfall

Guava does best with abundant moisture; 1000–2000 mm is optimal. Rainfall should be well distributed throughout the year, and should not be less than 600 mm/year. Adequate moisture is required during vegetative growth, and for optimum fl owering and fruit development. The tree does tolerate drought for up to 6 months, but prolonged drought induces defoliation. New growth and

fl owers occur soon after the beginning of the rainy season. In the dry tropics, fl owering is greatly infl uenced by water availability. The ideal rainfall pattern for guava fruit production is alternating dry and wet conditions. Artifi cial cycling to induce fl owering attempts to mimic this wet and dry cycle. In regions with prolonged dry seasons, fl ower induction can be managed by irrigation.

Drought and very low humidity during fl owering drastically reduce fruit set, with almost complete post-set drop being observed. Low moisture conditions during fruit enlargement reduce fruit size and puree recovery, caused by shrinkage of the inner pulp and its separation from the inner rind. Water-stressed trees will drop most fruit of 1–2 cm in diameter following heavy irrigation or rain as the tree resumes vegetative growth.

Temperature

Guava does best in warm areas with abundant moisture. It will grow from sea level to elevations exceeding 1500 m, if frost-free (Maggs, 1984). The optimum temperature is reported to be 23–28°C, with fruit set signifi cantly reduced by temperatures outside of this range during fl owering (Fig. 5.1).

However, guava production in Hawaii thrives very well between 15.5°C and 32°C. In spite of guava being native to the tropics, it can produce in subtropical areas or at altitudes of up to 1700 m. This adaptability has led to it being found in many places of the world and sometimes viewed as an invasive weed. Young plants are reported to be killed at –2°C, if this temperature is prolonged. In areas where winter night temperatures are 5–7°C for a few hours a night, such as in Okinawa, growth ceases and leaves become purple.

Commercial production is diffi cult in subtropical regions with insuffi cient heat calories during the winter months, and the time from anthesis to fruit harvest can increase to 220 days.

Fig. 5.1. The effect of temperature during fl owering on guava fruit set. (After Huang, 1961.)

Low winter temperatures during the dry season lead to natural defoliation, and fl owering will commence as soon as warm weather and rainfall induce new growth fl ushes and fruit set. In some places, defoliation is induced by withholding irrigation during the winter (1–6 months) to protect the plant from cold damage (González et al., 2000).

Light

Light saturation for this typical C3 plant is high: greater than 925 μmol/m²/s photosynthetic photon fl ux. Guava does not show any visible response to photoperiod. Seedlings normally require 2–7 years before fl owering. Longer sunlight duration leads to greater shoot growth.

Wind

Guava, though hardy, does benefi t from windbreaks. Trees grafted on seedling rootstocks have tap roots that provide substantial anchorage. However, trees produced from rooted cuttings are subject to uprooting by winds of 65–80 km/h for the fi rst 3 years, probably because of faster top growth than root growth, and the shallower root system of these plants in relation to seedling roots. Trees exposed to prevailing winds of 16–32 km/h gradually develop branches away from the winds, with little branch growth against the wind.

Windbreaks are crucial if high-quality dessert-type cultivars are being grown for the fresh market.

GENERAL CHARACTERISTICS Tree

Guava is a shrub but, under high-moisture conditions, will grow to 6–9 m in height and spread, with trunk diameters of 30 cm or more. The trunk is short, freely branching from the base. Under cultivation, a single trunk tree is developed by proper pruning and training. The bark is smooth but peeling, and greenish-brown to brown in color. Branches are pliable and hence rarely broken by winds. The leaves, arranged in pairs, are oblong or oval, 10–18 cm in length, smooth on the upper surface, fi nely pubescent on the undersurface and prominently veined (Fig. 5.2). Young green twigs are square, becoming rounded as they age.

Flowers

Flowers occur singly or in clusters of two to three at the leaf axils of current and preceding growth (Fig. 5.2). The perfect bisexual fl owers are white and 2.5–3.5 cm in diameter, with four or fi ve petals, numerous stamens and one

style. The tubular calyx encases the bud and splits into four or fi ve segments at anthesis. The ovary is inferior with four or fi ve carpels, each containing numerous ovules in axile placentation. Floral morphology favors self-pollination, but considerable cross-pollination occurs. Flowers open between 5 and 7 am, depending on the cultivar and morning temperatures; the calyx splits on the previous day. The anthers usually dehisce at anthesis or shortly before. Bees are the principal pollinators. It takes approximately 30 days from fl oral initiation to anthesis, and approximately 3.5 months from anthesis to fruit maturation. Two fl owering peaks occur in India and Hawaii. These natural peaks can be altered by changing weather conditions or cultural manipulation (Figs 5.3 and 5.4).

Pollination and fruit set

Natural pollination

Most guava clones have few problems with fruit set. Guava pollen generally has high rates of germination, except for triploid clones such as ‘Indonesian Fig. 5.2. The leaf, fl ower and fruit of guava.

Seedless.’ Fruit set in the triploid cultivars is good when grown together with diploid clones as a pollen source. Fruit set as high as 90% is obtained when fl owers 48 h old are pollinated. The period of stigma receptivity in

‘Beaumont,’ a Hawaii cultivar, is about 48 h. Post-fruit-set drop does occur as a result of factors other than pollination.

Some degree of self- and cross-incompatibility among guava clones has been shown; some combinations are totally incompatible, while reciprocal crosses produce some fruit (Table 5.1). ‘Beaumont’ produces 100% fruit set when self-pollinated and 60–80% fruit set by cross-pollination with other guava cultivars (Ito and Nakasone, 1968). These incompatibilities are the result of inhibition of pollen-tube growth in the style.

Fruit set by chemicals

Use of growth regulators has been tried, primarily to produce seedless fruit.

Auxin-like compounds do not reduce fruit drop. Fruit set is increased when 50 μg/ml gibberellic acid is applied, and the fruit contain fewer seeds and

Defoliate, Prune and Fertilize

Fruit Thinning and Bagging

Fig. 5.3. The steps involved in cycling guava trees for fruit production. The relationship between month of cycling, induced by pruning and fertilizing, and days to fruit harvest (after Bittenbender and Kobayashi, 1990) and the relationship between days to harvest from cycling and the duration fruit are available for harvest (H.C. Bittenbender, unpublished data) on the island Kauai, Hawaii. Fruit thinning and bagging are only used for the production of dessert fruit, not processing fruit.

Cycling to Harvest (Days) Harvest Duration (Days)

Cycle to Harvest (Days)

improved quality characteristics (e.g. total soluble solids, ascorbic acid, reduced fruit drop). When unopened fl ower buds are emasculated and styles cut off , and the gibberellic acid–lanolin mixture is applied to the cut surface, seedless fruit are obtained. Fruit obtained by this treatment are larger than those from untreated fl owers (Shanmugvelu, 1962). The fruit, however, show six to eight prominent ridges and swelling at the calyx end.

Fig. 5.4. Change in the monthly production of guava in 1975, when cycling was not used, and in 1990, when a major portion of Hawaiian production was cycled to give a single fl owering peak.

Table 5.1. Cross-compatibility of some guava clones as percentage mature fruit from self- and cross-pollination (Ito and Nakasone, 1968).

Female parent

% Fruit set Male parent

7197 7199 Beaumont Lucknow

Indonesian Seedless

7197 67 33 33 29 0

7199 33 64 50 50 0

Beaumont 62 67 100 100 0

Lucknow 57 33 33 27 0

Indonesian Seedless 57 14 33 0 0

Fruit

The fruit is botanically a many-seeded berry, varying in size from 2.5 to 10 cm in diameter (Fig. 5.2). The shape can be globose, ovoid, elongated or pear-shaped. The skin is yellow when ripe, while the fl esh can be pink, salmon, white or yellow. The skin texture can be smooth or rough. The inner wall of the carpels is fl eshy and of varying thickness, and the seeds are embedded in the pulp (Fig. 5.2). Flavor and aroma vary widely among seedling populations.

There are low-acid, sweet types, bland types that are low in both sugars and acidity, and high-acid types. The undesirable musky aroma is more pronounced in the fully ripened low-acid, sweet types.

Fruit growth follows a simple sigmoid curve (Fig. 5.5) and pulp growth parallels total fruit growth. The time from anthesis to harvest can vary from about 120 days to more than 220 days (Fig. 5.3), depending on the temperature during fruit development. Cultivars also vary by up to 60 days from anthesis to fruit maturity.

CULTIVAR DEVELOPMENT