References: G. Timpanaro in Basile (1996) for 1983 — 1995 and the Chamber of Commerce, Industry, Craftwork and Agriculture of Catania for 1996 — 1999. These prices refer to late-ripening fruits, which were converted to constant currency using the coefficients calculated by ISTAT
References: G. Timpanaro in Basile (1996) for 1983 — 1995 and the Chamber of Commerce, Industry, Craftwork and Agriculture of Catania for 1996 — 1999. These prices refer to late-ripening fruits, which were converted to constant currency using the coefficients calculated by ISTAT
10.2), which refer to the fruit still on the plant with harvesting charged to the buyer, decreased in real terms by 25 to 30% from 1983 to 1999, mostly due to the expanding supply. This, together with a rise in production costs, has led to a drop in profits. The high values in 1986, 1994, and 1995 reflect high-quality cactus pears, indicating consumer preference.
Opuntias are cultivated in subtropical arid areas, with mild winters (average air temperature > i0°C) and hot summers, where the annual rainfall ranges from 100 to 600 mm, and with a well-defined dry season that may last 2 to 5 months. Where no rainfall occurs during fruit development, or where rainfall is annually less than 300 mm, cactus pear needs irrigation to ensure economic cropping. In most areas where cactus pear is cultivated for fruit production, the plant has a period of no visible meristematic growth. This period usually coincides with the winter, with its short photoperiod and low temperatures. Indeed, high temperatures preceding bud differentiation reduce flower bud formation (Nerd et al. 1991; Nobel and Castañeda 1998), but the winter chilling requirement has never been quantified. On the other hand, cactus pear plantations for fruit production occur in the Canary Islands and in the valley of Catamarca in northwest Argentina, where less than 200 chilling hours accumulate during the winter.
In its native highlands of Mexico, cactus pear is cultivated in semiarid areas, where the annual rainfall is concentrated in the summer during the fruit development period. In the Mediterranean Basin, Middle East, North and East Africa, Argentina, California, and Chile, the dry season coincides with the long and hot summer, when vegetative and reproductive growth occur. For instance, cactus pear in Chile is cultivated in the Santiago metropolitan area, where the average monthly air temperature is 22°C in summer (January) and io°C in winter (August). The dry season lasts 4 to 5 months, and annual rainfall averages 350 mm (Sudzuki et al. 1993). In Italy, the species is cultivated for fruit production in Sicily, where the climate is Mediterranean, with mild, rainy winters and hot, dry summers. The average annual temperature is i6°C, being 25°C in July/August and i5°C in October/November during fruit development. Annual rainfall is between 400 and 600 mm, with a 4-month dry season (June-September). In Israel, the species is cultivated in the Negev Desert, where the lowest average monthly temperature is i3°C in January and the highest temperatures (25°C) occur from June through October; annual rainfall ranges from 40 to 200 mm. In South Africa, the Eastern Cape and the Northern Province receive summer rainfall, and in the Western Cape rainfall is concentrated in the winter. The Northern Province and the Ciskey region are the most important areas for specialized plantations, and the earliest fruit crops come from the subtropical areas near the Tropic of Capricorn. These provinces have long, hot summers and mild winters, with an extremely uneven rainfall occurring mainly in the winter and less than 500 mm annually (Brutsch and Zimmermann 1993; Brutsch 1997). In all areas, the average annual temperature is above i5°C, average monthly temperature ranges from i0°C in winter to 26°C in summer, and from i4°C to 25°C during fruit development and ripening.
The species occurs over a wide range of soils. A soil depth of 60 to 70 cm ensures the development of the shallow root system. Soils with poor drainage, a high water table, or a superficial impermeable layer or hardpan should not be used for planting. Clay content should not exceed 20% to avoid root rotting and reduced root and canopy development. Cactus pear is not salt-tolerant; 50 to 70 mM NaCl should be considered the upper threshold for profitable growing.
Many species of the Cactaceae produce edible fruits (Chapters 9 and ii). Among the approximately i,600 species in this family, the genus Opuntia has the most relevant role in agriculture. In the Mexican highlands, the center of genetic diversity for all opuntias (Pimienta-Barrios i990; Mondragon-Jacobo and Pimienta-Barrios i995), fruits come from wild plants of Opuntia lindheimeri Engel., O. streptacantha Lem., O. megacantha Salm-Dyck, and O. joconostle Web; O. amyclaea Ten. and O. ficus-indica are cultivated for fruit production on about 60,000 ha of specialized plantations (Pimienta-Barrios i990). Natural hybrids are common in both cultivated and wild populations (Pimienta-Barrios and Munoz-Urias i995). In South America, the United States, Africa, and the Mediterranean Basin, O. ficus-indica is the only species cultivated for fruit production. Spontaneous forms have a diploid (2n = 2x = 22) or a tetraploid (2n = 4x = 44) chromosome number, whereas cultivated varieties have a polyploid (2n = 6x = 66 or 2n = 8x = 88) chromosome number in Mexico and Italy (Mazzola et al. i988; Pimienta-Barrios and Munoz-Urias i995).
Cultivars for fruit production can be distinguished by the color of the fruit peel and the ripe flesh, which can be red-purple, yellow-orange, white-cream, or greenish. Red, yellow, and white fruits are present in all the cultivated areas, but green fruits, with a greenish-white flesh, are found only in Chile and Peru (Mondragon-Jacobo and Pimienta-Barrios i995). Cultivars also differ in plant shape, vigor, fertility, cladode and fruit size, fruit ripening time, seed count, and ability to reflower (Pimienta-Barrios i990; Wessels i988; Barbera and Inglese i993). The largest diversity in plant shape occurs in the South African germplasm. Wessels (i988) describes bushy-type, columnar (long-cladode), and round-cladode plants, which also differ in terms of vigor, chilling requirement, and cladode fertility, and eventually require different orchard design in terms of plant spacing. The largest genetic diversity occurs in Mexico and South Africa, whereas in the other countries only a few cultivars have been described and are commercially cultivated. Nevertheless, within the same cultivar, different clones can be identified. For instance, in Italy and Argentina, at least 3 to 4 clones of the local 'Gialla' or 'Amarilla sin espinas' are distinguishable (Barbera and Inglese i993; Ochoa i997). Mexican cultivars show a great variability also in terms of fruit ripening time, with early ripening cultivars harvested in May ('Tapona de Mayo' and 'Pachona') or June ('Naranjona') and late ripening ones are harvested in September ('Cristalina') or October to November ('Fafayuco,' 'Cascaron,' and 'Charola'). Italian, Argentinian, and South African varieties do not show any marked variability in fruit ripening time.
The most appreciated fruits in the international markets have a yellow-orange flesh, such as 'Gialla' in Italy, Amarilla huesona' in Mexico, 'Ofer' in Israel, 'Malta,' 'Gymnocarpo,' and 'Direkteur' in South Africa, and 'Amarilla sin espinas' in Argentina. Red-purple or pink fruits, such as 'Algerian' in South Africa, 'Rossa' in Italy, or 'Pelon liso' and 'Rojo pelon' in Mexico, are also highly appreciated, particularly in the United States, where the 'Andy Boy' cultivar with pink-red flesh is grown in California (Bunch 1996). Recent studies in Italy show that consumers unfamiliar with this fruit are attracted by red fruits, which they buy first (Asciuto et al. 1997; Battaglia 1997). Fruits with white or greenish flesh are prized only in regional or local markets, and their international trade is not large. White-flesh fruits are very sensitive to postharvest handling and to specific pests, such as Ceratitis capitata (the Mediterranean fruit fly).
Cactus pear is commonly propagated via cuttings. The use of 1-year-old potted plants has been successful in South Africa (Wessels 1988) and Italy (Barbera et al. 1993a), but, although the field growth response is satisfactory (Inglese et al. 1996), additional costs are incurred for nursery establishment, plant transportation, and planting, making it barely feasible economically. Both single and multiple cladode cuttings are utilized.
Single cuttings can be 1 to 2 years old, and their surface area and dry mass have a significant influence on successful rooting and subsequent budding in the field. A surface area of 500 cm2 or a dry mass of 70 to 100 g allow good plant growth (Barbera et al. 1993a; Inglese et al. 1996; Wessels et al. 1997). Other sources of variability of cladode rooting and subsequent plant growth in the field involve the age of the mother plant and its phytosanitary conditions, cutting planting depth, the cladode surface area left above-ground, soil temperature, and soil water content (Brutsch 1979; Wessels et al. 1997). Adventitious roots originate from phloem cells near the areole, while the cambium remains dormant. The stimulus to cell dedifferentiation and multiplication may occur within 2 days after the cuttings are placed in contact with the soil, and primordia emergence may occur within 14 days (Fabbri et al. 1996). The cutting may develop 60 g of root dry mass in the first year (Inglese et al. 1996). Cuttings are usually planted upright, with half of the cladode placed below ground.
A multiple cladode cutting is made of a 2-year-old cladode bearing, on its crown-edge, one or two 1-year-old daughter cladodes. The advantage for such multiple clad-ode cuttings is the rapid formation of plant structure, which results in earlier fruiting after planting. Similar results can be obtained by planting, in a single hole, two cuttings, spaced 0.4 m apart, or three to four cuttings placed in a triangle or square and spaced 0.3 m apart. This method ensures fast canopy development, but requires a large amount of planting material (Mondragon-Jacobo and Pimienta-Barrios 1995). Cuttings have to wilt 4 to 6 weeks in a dry, shaded environment before being planted to let the wound dry and prevent rot at the cut surface. Bordeaux paste, as well as 0.4 milliliter of methridathion or 1 g liter-1 of copper oxychloride, are often applied to cuttings before planting.
Late spring is the best time for planting. Indeed, roots and cladodes reach their highest growth rate during late spring and early summer (Barbera et al. 1993a; Wessels 1988), and soil water content in late spring is high enough to allow root development in areas with winter rainfall, whereas cuttings benefit from rains that occur after planting in areas with summer rainfall (Pimienta-Barrios 1990; Barbera and Inglese 1993; Sudzuki et al. 1993; Wessels 1988). Planting at the end of the summer slows the development of the root system and canopy, due to low winter temperatures and reduced light (Barbera et al. 1993a); moreover, weeds compete more efficiently, and winter rains can promote root rot. If cuttings are planted during the hot and dry season without irrigation, root growth and budding are scarce, and cladodes readily wilt and eventually die because of high temperatures and low humidity. Even with summer rainfall, the time for rooting and cladode growth is often too short.
Good orchard design, in terms of plant layout and spacing, includes (1) hedgerow systems, with plants placed closely along a row, and (2) a square or rectangle layout, with plants trained to be globe-shaped and well separated from each other. Plantations established in Italy during the 19 th century were laid out in hedgerows, with plants placed every 0.5 m along rows spaced 6 to 8 m apart (Barbera et al. 1992a). Orchards are established with a hedgerow layout in Israel and California (Bunch 1996), with cuttings placed at 1.5 to 4 m intervals along rows spaced 4 to 6 m apart (830-1,666 plants ha-1). Pimienta-Barrios (1990) suggests a hedgerow layout for farms smaller than 5 ha, with close spacing (2-3 m) along rows spaced 5 m apart (1,110-1,666
plants ha-1). Close spacing along a row increases the number of fertile cladodes per unit area in the early stages of orchard life. Close spacing results in continuous and dense canopies, which require a high pruning frequency and intensity to avoid within-plant shading and reduction of fruit quality. Canopies that are too dense reduce cladode fertility, facilitate cochineal infestations, and reduce the efficiency of pest control operations.
If the plants are spaced in a square or rectangular layout, they are usually trained to a bushy-type globe shape. In Italy, plant spacing ranges from 4 x 6 m (416 plants ha-1; Fig. 10.2) to 5 x 7 m (290 plants ha-1). In Mexico, Pimienta-Barrios (1990) recommends, for farms with more than 20 ha, distances of 4 m along rows spaced 5 m apart (500 plants ha-1). In South Africa, plants are spaced according to the cultivar growth habit. Bushy-type plants develop a continuous hedgerow because of their open growth form. The general recommendation for bushy-type culti-vars is 2 to 3 m along rows spaced 4 to 5 m apart (6661,250 plants ha-1). The upright types can be spaced 3 to 4 m apart along rows spaced 4 to 6 m apart (415-830 plants ha-1; Wessels 1988). Because cladodes are generally planted with their planar surfaces parallel to the row direction, the rows should be oriented north-south to maximize light interception (Nobel 1988).
Cactus pear plants can be trained to a globe shape of various sizes (height and width) or canopy densities based on cultivar growth habit, plant spacing, and environmental conditions. In many cases, plants are not trained and are pruned only occasionally. The globe-shaped plants have 3 to 4 main stems and a high number of fertile cladodes, mostly distributed around the outer portion of the canopy. Pruning can regulate resource allocation among the various canopy sinks and can maximize light availability within the canopy to support cladode growth, flower bud formation, and fruit growth. Moreover, pruning facilitates pest control, fruit thinning, and fruit harvest. Garcia de Cortázar and Nobel (1992) defined the stem area index (SAI) that maximises plant productivity in terms of biomass. High planting densities lead to an extremely high accumulation of dry matter into vegetative growth, but it reduces allocation to the fruit (Garcia de Cortázar and Nobel 1992).
This is the case for orchards for nopalito production (Chapter 13), which involve vegetative instead of reproductive growth. However, optimal SAIs for fruit production are unknown, as are strategies for annual and long-term pruning.
Even though pruning represents one of the major costs of orchard management, information on it is scarce (Basile and Foti 1997). Most net CO2 uptake is by current-season and 1-year-old cladodes, with older cladodes serving as a pool of stored carbohydrates and nitrogen that can be used to support fruit and current-season cladode growth (Luo and Nobel 1993; Inglese et al. 1994b; Nerd and Nobel 1995). Flower buds differentiate on terminal, well-exposed 1-year-old cladodes, whose dry weight exceeds a minimum value for its surface area by at least 33 g (Garcia de Cortázar and Nobel 1992).
Moreover, cladode shading affects fruit growth in terms of size and ripening time (La Mantia et al. 1997). To avoid alternate year bearing, every year the plant must produce the same number of new cladodes, which will bear fruit 1 year later; new cladodes develop on 2-year-old and even older cladodes (Inglese et al. 1998a). Thus, to get an accurate seasonal balance between vegetative and reproductive growth, the plant needs a constant number of 1-year-old cladodes (for fruit production) and 2-year-old cladodes (for new cladode production). As a rule of thumb, to maximize their development, no more than two daughter cladodes should be retained on a parent cladode. Pruning also involves the removal of the current season's cladodes developing on fertile cladodes. Two-year-old cladodes, which have already produced fruit, should be removed if there is no vegetative activity. The number of fruiting cladodes left on a plant every year depends on plant spacing, and ranges from 100 to 120 for 350 to 400 plants ha-1 to 20 to 30 for 1,000 to 1,200 plants ha-1. The closer the plant spacing, the higher the pruning intensity and frequency needed.
Pruning should be carried out when temperatures are high enough to make the cut dry out quickly, which prevents rot and scabies. Cladodes cut at their basal edge can be chopped and left between the rows. In South Africa, Wessels (1988) suggests pruning from May to July after the fruit harvest, when the plant is no longer actively growing. New cladodes will develop the following spring, a strategy feasible in regions with dry winters. In Mexico, Pimienta-Barrios (1990) suggests pruning from November to March, during the dry and cold season. Barbera and Inglese (1993) suggest that May to June is the best time for pruning. Plants should be topped at 2.0 to 2.5 m in height, which avoids the use of ladders for fruit thinning and fruit harvest.
Most plants have lower fruiting potential and cladode renewal 25 to 30 years after planting. At this stage renewal pruning can be an alternative to orchard replanting. Rejuvenation can be achieved by pruning the plants back to 4- to 5-year-old cladodes (Mulas and D'hallewin 1990). Heavier pruning back to the lignified cladodes can also be practiced to resume growth of weak plants. The plant generally resumes fruiting 2 to 3 years after such pruning, depending on the pruning intensity.
The number of flower buds per fertile cladode varies according to cultivar (Barbera et al. 1991; Wessels 1992), season (Barbera et al. 1991; Nerd et al. 1993; Inglese et al. 1998a), cladode age (Inglese et al. 1994a, 1998a), and dry-weight accumulation (García de Cortázar and Nobel 1992). Cladodes bearing 3 to 7 flowers are the most common and account for 50 to 60% of plant fertility (Inglese 1994), but well-exposed cladodes might bear, along their crown-edge, 25 to 30 flower buds, most of them setting fruits. Net photosynthesis of developing fruits is limited, and its contribution to fruit carbon demand is greatest during the early stages of fruit development (8-10%; Inglese et al. 1994b). Fruits obtain most of their assimilates from their mother cladode, but the sink demand to support the growth of fruit and the current season's cladodes involves a substantial flow of stored carbohydrates from basal cladodes (Luo and Nobel 1993; Inglese et al. 1994). The carbon demand is greatest when more than six fruits develop on 1-year-old fruiting cladodes, and particularly during the last 3 to 4 weeks of fruit growth, when the flesh rapidly develops and accumulates sugars (Barbera et al. 1992b). At this stage, the import of photoassimilate is 30% and 70% of the fruit dry weight gain for cladodes with 5 and 15 fruits, respectively (Inglese et al. 1994b).
The fruit also competes with the current-season's developing cladodes, which show a higher growth rate than the fruit for most of the fruit development period. The fruit becomes a major sink during the final swell of the flesh, and this coincides with a consistent reduction in the growth rate of the current-season's cladodes (Inglese et al. 1999). Indeed, the fruit growth rate and harvest size decrease with fruit number per cladode, when more than six fruits are left on a cladode (Brutsch 1992; Inglese et al. 1995b). For South African cultivars, Wessels (1988) recommends retaining no more than 9 to 12 fruits per cladode to increase fruit harvest size. Cladodes with more than 10 fruits show irregular and delayed ripening. In areas with no rains during fruit development, thinning must be accompanied with irrigation to get a significant increase in fruit size and percentage flesh (La Mantia et al. 1998). The effect of fruit thinning depends also on the number of fruits per cladode prior to thinning; the longer the time that the fruits are retained on a cladode, the greater the effect of the fruit number on final fruit size (La Mantia et al. 1998). Thinning can be performed from budbreak to the early stages of fruit development, but the most appropriate time is 10 to 20 days after bloom, when differences in fruit size are clear enough to allow selective thinning and flesh development is still negligible (Barbera et al. 1992b). Removing fruits 20 to 30 days after set reduces the effectiveness of thinning (Inglese et al. 1995b). Cladode size (surface area and thickness) and within-canopy position should also be considered to determine optimal thinning ratios.
Unlike many other fruit crops, relatively little information concerning cactus pear nutrient demand and economy is available (Nobel 1988). Early investigations (Monjauze and Le Houerou 1965) demonstrate that manure application improves Opuntia biomass productivity. Similarly, fertilization with nitrogen (N) increases biomass production (Nobel et al. 1987), and phosphorous (P) application significantly increases fruit production (Gathaara et al. 1989). Cladode tissue N and potassium (K) concentrations are positively correlated, and sodium (Na) concentration are negatively correlated with fruit yield (Karim et al. 1998). Moreover, 1-year-old cladodes that produce new organs have a higher level of nitrate at the beginning of the season than do nonproductive cladodes (Nerd and Nobel 1995). The concentration of N in the parenchyma of fruiting cladodes decreases rapidly during fruit development, and K concentration is higher for nonproductive than for fruit-bearing cladodes. The magnesium (Mg) concentration is correlated with fruiting, but the calcium (Ca) content increases throughout the season, with no relation to cladode fertility (Inglese and Pace 1999).
Extensive N application soon after harvesting the summer crop promotes an additional budding in the autumn (Nerd et al. 1991, 1993), but it does not result in any increase in the main crop the following summer. Injection of KNO3 promotes flower bud induction (Aguillar-Becerril 1994), and increased N concentrations in fertile cladodes reflect a rise in soluble reduced-N compounds, which is associated with flower bud production. Neither K nor P contents are correlated with the occurrence of the autumn flush of flower buds (Nerd et al. 1993). Fruit mass and soluble sugars increase with N fertilization, but high applied N (200 kg ha-1) results in excessive vegetative growth (Potgieter and Mkhari 2000). Nitrate content is highest in the parenchyma and at the basal edge of the cladodes (Nerd and Nobel 1995).
Nutrient concentration in cladodes varies with age, position, fruit load, and season. Nitrogen concentration varies from 0.4 to 2.2%, with the highest values occurring in 2- and 3-year-old cladodes that serve as a reserve for the growth of new organs (Nerd and Nobel 1995; Inglese and Pace 1999; Potgieter and Mkhari 2000). Higher concentrations may result in excessive vegetative growth, a decrease in fertility, a delay in ripening, and a reduced fruit color. Claassens and Wessels (1997) obtained optimum fruit yield at a N concentration of 0.94 to 0.96%. Inglese and Pace (1999) found the highest fruit yield per cladode at 0.8% N. Concentrations of K and P reach 0.4 to 3.5% and 0.06% to 0.2%, respectively. Gathaara et al. (1989) found P and N fertilization to be beneficial to the yield of young plants of Opuntia englemannii, at least for the first year of growth.
Because of its high drought resistance and high water-use efficiency, cactus pear is usually cultivated without irrigation. However, in areas with no summer rains and where annual rainfall is less than 300 mm, the plants require supplementary irrigation to get adequate yields and good fruit quality (Barbera 1984; Mulas and D'hallewin 1997). Even in areas where summer rainfall of 300 to 600 mm is sufficient to ensure high yields and regular fruit development, dry winter conditions may result in late and poor flower bud induction, which in turn leads to late and low yields (Bowers 1996; Nerd et al. 1989; Van Der Merwe et al. 1997). Under these conditions, drip irrigation with daily, low amounts (1-2 mm day-1) ensures high yields and good fruit growth. Moreover, light irrigation in early summer or during fruit swelling is desirable, particularly in light soils, to avoid wide variations in soil moisture, which promote fruit cracking (Wessels 1988). The counteracting effect of water deficit on fruit size increases with the number of fruits per cladode; on the other hand, irrigation alone cannot make up for reduced size when there are a high (> 10) number of fruits per cladode (La Mantia et al. 1998).
Where the species is intensively grown for fruit production, irrigation is common in areas with dry summers, particularly in Israel, Italy, and Chile. Both cladode fertility and fruit growth benefit. Barbera (1984) reports that two to three irrigations, with an annual amount of 60 to 100 mm, applied during the earliest stages of fruit development (within 40 days after bloom), increase yield, fruit size, and flesh percentage. Irrigation may also increase seed weight and peel thickness (Mulas and D'hallewin, 1997); however, there is no clear influence on sugar content, fruit firmness, or flavor. In areas where vegetative growth occurs during the dry period, irrigation enhances plant development in terms of both cladode number and size (Mulas and D'hallewin 1997).
Traditional irrigation methods, such as basin irrigation, may result in extensive leaching and are not adequate because of the shallow root system of the plants. If irrigation is done only two to three times during the dry season, the use of furrows may be easy and inexpensive. Localized micro-sprinklers, which cover a relatively large soil surface area with small volumes, meet the characteristics of the shallow root system of cactus pear. Drip irrigation can be also utilized, particularly when irrigation is applied during most of the season, as in Israel. Seasonal volume ranges from 60 to 80 mm in Italy to 250 to 300 mm in South Africa to 500 mm supplied in Israel (Barbera 1984; Nerd et al. 1989; Van Der Merwe et al. 1997; La Mantia et al. 1998). NaCl in irrigation water should not exceed 25 mol m-3. Na accumulates mostly in the roots, whereas, when using salty water, Cl content increases both in the roots and in the cladodes (Nerd et al. 1991).
The harvesting season for cactus pears lasts for a relatively long time. In the Northern Hemisphere, the main summer crop lasts from late June to mid September, depending on cultivar and environmental conditions. The earliest crop comes from North Africa and a late crop comes, in Italy, from October to November (Fig. 10.3), as a result of the removal of the main spring flush (Barbera et al. 1992a; Figure 10.1). A winter crop comes in Israel, following extensive fertilization and irrigation applied soon after harvesting the summer crop in July to August (Nerd et al. 1993). Extremely mild winter temperatures allow a prolonged harvest season for cactus pears in Salinas, California, where fruits are picked from September to March (Inglese 1995). In the Southern Hemisphere, the summer crop is harvested from December to February, with a second natural crop occurring from July through September in Chile (Sudzuki et al. 1993) and an artificially induced second crop that ripens in March to April in South Africa (Brutsch and Scott 1991). In the native areas of Mexico, the harvest season varies with environment and cultivar, and goes from May through October (Pimienta-Barrios 1990; Pimienta-Barrios and Munoz-Urias 1995).
The length of the fruit development period and the ripening time are cultivar-dependent but show large with-in-plant variability (Inglese et al. 1995a). Fruit ripening is asynchronous, even at a cladode level, and two or three pickings are required to harvest the entire crop. The harvest period of most cultivars may last for 2 to 6 weeks, depending on season and environment (Inglese 1994). The time of flower bud burst, cladode exposure to light (La Mantia et al. 1997), and fruit load per cladode (Inglese et al. 1995a) are the main sources of variability of the fruit ripening time at the plant level (Inglese et al. 1995a, 1999; La Mantia et al. 1997). Fruit development occurs over a wide range of climatic conditions throughout the world, including winter and summer seasons, and the time required to reach commercial harvest maturity varies from 70 to 150 days (Brutsch 1979; Pimienta-Barrios 1990; Nerd et al. 1991; Barbera and Inglese 1993; Inglese et al. 1999). On the other hand, the accumulated thermal time from bloom to commercial harvest is rather constant (40 x 103 degree hours), and different accumulation patterns of thermal time apparently account for the variability in fruit ripening time that occur by year and environment for the same genotype (Inglese et al. 1999).
Ripening is also sensitive to temperature. For example, high temperatures (> 25°C) result in a rapid onset of ripening that may affect fruit size and reduce postharvest durability, whereas low temperatures (< i5°C) delay fruit ripening time and result in a prolonged fruit harvest period at plant and orchard levels. When daily temperatures fall below i2°C, ripening slows and fruits may overwinter and ripen the next spring (Barbera and Inglese 1993). Temperatures above 35°C, and associated low air humidity, may cause sunburn damage on fruits (Brutsch 1992). Differences in temperatures during fruit development involve changes in fruit characteristics, such as size, shape, peel thickness and color, percentage flesh, sugar content, and seed count (Nerd et al. 1991; Barbera and Inglese 1993; Inglese et al. 1999). Fruit should be harvested when peel color changes, a time when the umbilical crown is still slightly green. At this stage, fruits can withstand a substantial storage and marketing period. At harvest, the concentration of reducing sugars is 90% of that for fully ripe fruits and should not be less than 13% by fresh weight; pulp firmness, as measured with an 8-mm cylinder, should not be less than 8 kg cm-2 (Pimienta-Barrios 1990; Barbera et al. 1992b). Fully ripe fruits are too soft to be stored and are difficult to handle.
Fruits should be harvested early in the morning, when their internal temperature is not higher than 25°C, and when the glochids are still wet and adhere to the peel. To
reduce postharvest decay caused by wound-infecting pathogens, fruits should be removed with a knife so as to leave a small piece of the mother cladode at the edge of the cut (Barbera and Inglese 1993). Subsequent exposure of fruits to room temperature (curing) is recommended to promote wound healing, the drying of the piece of clad-ode, and its ready detachment during handling and packaging (Chávez-Franco and Saucedo-Veloz 1985). Soon after harvesting, fruits are cleaned and brushed under a water spray or under suction to remove the glochids. Fruits are usually sorted according to size, color, shape, and overall appearance. Brushing involves rudimentary equipment, but it can be mechanized to increase efficiency and reduce fruit damage. Postharvest losses can be high, depending on cultivar, stage of maturity, environmental conditions, and harvesting method (Castillo-Castillo and Pimienta-Barrios 1990; Cantwell 1995; Schirra et al. 1999a).
Fruit productivity of Opuntia ficus-indica is extremely variable from country to country. Yields of 20 to 30 tons ha-1 are reported in Israel and Italy (Barbera and Inglese 1993; Nerd and Mizrahi 1993) and 10 to 30 tons ha-1 in South Africa (Wessels 1988; Brutsch and Zimmerman 1993). Much lower yields occur in Chile, 6 to 9 tons ha-1 (Sudzuki et al. 1993), and Mexico, where yields range from 4 tons ha-1 in the north to 9 tons ha-1 in the central area (Federal District) and 20 to 25 tons ha-1 in the south
(Pimienta-Barrios 1990; Flores Valdez et al. 1995). In Israel, Nerd and Mizrahi (1993) report fruit yields of 18 tons ha-1 for a 4-year-old orchard with plants spaced 4 x 1.5 m apart. In the Salinas Valley of California, Bunch (1996) reports an average of 12 tons ha-1, with peaks of 25 tons ha-1, for planting densities of 370 to 430 plants ha-1 (plants spaced 6 x 4 m or 6 x 4.5 m). Impressive yields have been measured for young O. ficus-indica cv. 'Gialla' plantations in Argentina (Catamarca), where climatic conditions allow extremely fast plant development (P. Inglese, personal observation). The wide variability in yield depends on orchard design (plant spacing), cultural practices, environmental conditions (including soil type), and cultivar fertility.
Productivity also varies at the plant level. Differences in planting material, related to the rooting ability of cuttings and subsequent canopy development, account for discrepancies in yield potential 4 or 5 years after planting (Brutsch 1979; Wessels et al. 1997). Biennial bearing—with differences of 40 to 50% in fruit yield between off and on years—has been reported in Italy (Barbera et al. 1991), Mexico (Pimienta-Barrios 1990), and South Africa (Brutsch 1979), and also for natural stands of Opuntia engelmannii in the Sonoran Desert (Bowers 1996). Mismanagement of pruning (Inglese et al. 1998a), plant age, and interactions between developing fruits and flower buds (Barbera et al. 1991) or vegetative versus reproductive growth (Bowers 1996) may account for this behavior.
Plants begin to yield 2 to 3 years after planting, reach their maximum potential 6 to 8 years after planting, and bear for 25 to 30 years or even longer, depending on pruning and overall orchard management. For a mature plant, most (80-90%) 1-year-old terminal cladodes bear fruit and account for 90% of the annual yield. However, they show a wide fertility range, depending on plant age, environmental conditions, and their state of growth, as indicated by the accumulation of dry matter relative to the cladode surface area (Garcia de Cortázar and Nobel 1992), their orientation and exposure to light, and vegetative versus fruit competition (Inglese et al. 1999). Two-year-old cladodes are less fertile than 1-year-old ones; they usually account for no more than 10% of the commercial yield, but may become an important source of fruits in the off years and in older plants; they have a poor ability to reflower, and their fertility usually does not exceed 6 to 10 fruits per cladode (Nerd et al. 1993; Inglese et al. 1994a; Inglese et al. 1998a). However, 80 to 95% of the vegetative buds, which will become fruiting cladodes 1 year after formation, differentiate on 2-year-old cladodes (Inglese et al. 1998a).
Strategies to increase productivity involve management to raise the number of fertile cladodes per plant and increasing the planting density. To get an annual yield of 20 tons ha-1, given a cladode fertility of 6 fruits and a fruit size of 100 to 120 g, 28,000 to 30,000 fruiting cladodes are needed per hectare. This means 80 to 90 fertile cladodes on bush-type plants placed 6 x 5 m apart (335 plants ha-1) or 28 to 30 fertile cladodes per plant for high density, hedgerow-like orchards with plants spaced at 5 x 2 m (1,000 plants ha-1). Dry matter partitioning of mature, fruiting cactus pear plants indicates a seasonal competition between vegetative and reproductive growth, involving fruits, newly developing cladodes, and the secondary growth of older cladodes. Current season's cladodes are the strongest sink for most of their growth period, but the fruit becomes the strongest sink during the last stage of fruit growth; secondary growth is the weakest sink, and old cladodes can contribute to the carbon budget through the remobilization of their stored carbohydrates (Luo and Nobel 1992; Inglese et al. 1994b). Seasonal values of harvest index, a term indicating the relative partitioning of current season's dry matter to the fruits, range from 35 to 46% (excluding root growth) and are similar to those reported for deciduous fruit crops. This demonstrates, once again, the high efficiency of cactus pear as a fruit tree.
One of the most striking features of Opuntia ficus-indica is certainly the ability of its cladodes to reflower at different times, naturally or after inductive practices are applied (Nerd and Mizrahi 1997). In Chile, terminal cladodes reflower naturally in May to June, and the resulting second crop comes in July to September, with 50 to 60% lower yield than the major summer crop (Saenz Hernandez 1985; Sudzuki et al. 1993). An autumn crop also occurs in the Santa Clara Valley of California, with fruit ripening in winter and spring (Curtis 1977; Bunch 1996). In Israel, the off-season crop develops on the current season's terminal cladodes that bear fruit a few months after extensive N fertilization (80-120 kg ha-1) and irrigation applied soon after harvesting the summer crop in July; the amount of this crop is rather low (20-30% of the summer crop), and decreases with plant age (Nerd et al. 1993). In Italy (Barbera and Inglese 1993; Inglese 1994) and South Africa (Brutsch and Scott 1991), a second flowering is obtained as a result of the complete removal of the spring flush of flowers and clad-odes. In this case, a plant produces once a year, whereas in Chile the natural reflowering allows for two crops per year.
The spring flush removal (scozzolatura, Fig. 10.1) takes place when the main bloom occurs, between the end of May and the last week in June in the Northern Hemisphere, and in October in the Southern Hemisphere. The new flower buds develop on the fertile cladodes of the natural flush, and the reflowering index, defined as the ratio of second versus first flush flowers, is highest for cladodes with a natural fertility of 5 to 10 flowers. The reflowering index sharply decreases with the number of flowers in the first flush (Inglese 1994). Removal time affects the cladode reflowering rate (Barbera et al. 1991; Brutsch and Scott 1991). Removing flowers at a pre-bloom stage results in the highest reflowering rate, whereas removing the spring flush after petal shedding reduces reflowering by 50 to 70% (Barbera et al. 1991; Inglese et al. 1998b). This decrease in reflowering, which occurs when flowers are removed at full bloom or after petal shedding, is related to an inhibitory effect on flower bud initiation (Barbera et al. 1993b) caused by gibberellic acid (GA3) diffusing from the flowers to the mother cladode (Inglese et al. 1998b). Indeed, Barbera et al. (1993b) demonstrate that GA3 applied within 6 days after the spring flush removal completely inhibits reflowering, indicating that the flower bud, induced the preceding spring (Cicala et al. 1997), is still in a reversible stage. The current season's developing cladodes also inhibit reflowering if they are not fully removed (Inglese et al. 1994a).
Fruits induced by removing the first flush flower buds have the shortest development period, ripening 15 to 20 days earlier than full-bloom fruits and 30 to 40 days earlier than fruits induced after removing post-bloom fruits.
The reflowering rate also depends on the environmental conditions at removal time, especially soil water content and air temperature. Indeed, the extent of reflowering greatly differs from year to year and with orchard location (Barbera et al. 1991; Brutsch and Scott 1991; Nieddu and Spano 1992). To improve reflowering in light soils with low water content, irrigation should be applied at the moment of spring flush removal. Scozzolatura should not be applied until 3 to 4 years after planting, when reflowering ability is still poor.
Fruit quality varies with cultivar and depends on several management, environmental, and physiological factors. Fruit growth potential is determined by effective pollination, hence seed count (Barbera et al. 1994; Pimienta-Barrios 1990, Nerd et al. 1991), but factors such as light (La Mantia et al. 1997), water availability (Barbera et al. 1998), temperature (Inglese et al. 1999), cladode fruit load (Wessels 1988; Brutsch 1992; Inglese et al. 1995b), and interactions between developing fruits and cladodes (Inglese et al. 1994b, 1999) may also play a substantial role in determining fruit growth potential, final fresh weight, and other quality attributes. Pruning, fruit thinning, and irrigation are the most powerful tools to maximize fruit size. Average fruit fresh weight varies with cultivar, from 100 to 240 g. Mexican cultivars such as 'Cristallina' and 'Burrona' may reach 240 g in fresh weight (Pimienta-Barrios 1990), whereas fruit weight of the Italian 'Gialla,' 'Bianca,' and 'Rossa' generally ranges from 100 to 160 g (Barbera and Inglese 1993). In South Africa, fruit fresh weight of cactus pear ranges from 100 g ('Algerian') to 180 g ('Nudosa'; Wessels 1988).
Export size fruit must exceed 120 g. The percentage of flesh, which should not be lower than 55%, is less variable than fruit size (Inglese 1994; Inglese et al. 1994a). It ranges from 60 to 65% for the Italian cultivars ('Gialla,' 'Bianca,' and 'Rossa'), but a wider range has been found in South Africa (Wessels 1988). In Mexico, a comparison between nine cultivars revealed a 40 to 60% range in size (Pimienta-Barrios et al. 1992). Low temperatures during fruit development promote an increase in peel thickness and a reduction of flesh growth, resulting in a low flesh:peel ratio (Nerd et al. 1993; Barbera and Inglese 1993).
Sugars, mainly glucose (6-8% on a fresh weight basis) and fructose (5-6%), accumulate rapidly when the flesh begins to grow, and harvest values should be at least 13% (Barbera et al. 1992). The genotype is the main source of variability in sugar content, with some Mexican varieties reaching 17 to 18% (Pimienta-Barrios 1990), while crop load or fruit position within the canopy do not affect sugar content as much. Low temperatures during fruit development result in a significant reduction of sugar content at harvest (Barbera et al. 1991; Nerd et al. 1993). Organic acid content is very low (0.03-0.12%, expressed as malic acid), and the pH ranges between 5.0 and 7.0 (Barbera et al. 1992b; Kuty 1992).
Seed number and the ratio between empty and normal seeds are among the most important factors defining fruit quality. Seed number per fruit ranges from 120 to 350, and the empty versus normal seed ratio is higher in Italian (0.44) than in Mexican (0.11) cultivars (Barbera et al. 1994). Seed weight changes with cultivar, ranging from 2.0 to 7.0 g per fruit (Parish and Felker 1997). The nutritional value is similar to peach fruit (150 kilojoule per 100 g fresh weight of digestible fraction). The ascorbic acid content is 20 to 30 mg per 100 g (Inglese 1994).
Cactus pear is a non-climacteric fruit with low respiration and ethylene production rates (Lakshminarayana and Estrella 1978; Lakshminarayana et al. 1979; Cantwell 1995), although a preharvest climacteric-like rise in respiration rate has been observed in fruit harvested at different stages of development (Moreno-Rivera et al. 1979). Cantwell (1995) indicates that fruit harvested at green, intermediate, and ripe stages produces similar levels of CO2, but sharp increases in respiration and ethylene rates are usually detected when fruits are removed from cold storage and placed in shelf-life simulating conditions (Schirra et al. i997a,b). This also depends on ripening status and storage duration (Schirra et al. 1999b). Postharvest changes of internal quality characteristics, such as pH, titratable acidity, soluble solids, acetaldehyde concentration, and ethanol concentration in the flesh, are low, whereas ascorbic acid concentration may decrease, depending on storage conditions.
The postharvest life span of the fruit is relatively short. Under shelf-life conditions, cactus pear fruits may deteriorate in a few weeks as a result of rapid aging and decay. However, in the i9th century, when adequate storage facilities did not exist, fruits wrapped with thin paper were preserved in dark, cool rooms for 3 to 4 months (Bazin 1979). Covering them with straw helps reduce the water loss rate. Rodríguez-Félix et al. (1992) found that a total water loss of about 8% affected the fruit's overall visual appearance. Fruit brushing to remove glochids adversely affects keeping quality and increases the rate of water loss and decay (Testoni and Eccher-Zerbini 1990). Common postharvest pathogens of cactus pears include fungal infections (e.g., with Alternaria spp., Botritis spp.,
Chlamydomyces spp., Fusarium spp., Penicillium spp.) and bacterial infections (Chessa and Barbera 1984; Rodriguez-Felix et al. 1992; Chapter 14).
Like most tropical and subtropical fruit species, when stored at temperatures below 8°C, cactus pears are susceptible to physiological disorders collectively known as chilling injury, which involve the appearance of dark spots on the peel (Chessa and Barbera 1984; Cantwell 1995). Such postharvest responses depend upon growing conditions, cultivar, and fruit ripening stage at harvest. For example, fruit of 'Verde' cultivated in Chile is resistant to chilling injury, as no visible symptoms occur after 2 months of storage at o°C (Berger et al. 1978), whereas fruits of Opuntia amyclaea and O. ficus-indica from Chapingo, Mexico, have chilling injury when stored at 8 to io°C for 15 days (Chavez and Saucedo 1985), and those of 'Gialla' grown in Italy exhibit severe injury after 14 days at 6°C (Chessa and Barbera 1984; Chessa and Schirra 1990).
Preharvest spraying with gibberellic acid increases fruit resistance to decay during cold storage but promotes susceptibility to chilling injury (Schirra et al. 1999a). Scanning electron microscopy indicates that this effect is related to a delay in peel maturation (Schirra et al. 1999b), and similar effects occur following preharvest sprays with 2o g/liter CaCl (Schirra et al. 1997b, 1999b). Fruits harvested at color change are less susceptible to decay but more prone to chilling injury than are fully ripe ones (Gorini et al. 1993). Fruits that ripen under high temperatures and low relative humidity are highly susceptible to chilling injury but less sensitive to rot decay, whereas fruits ripening at the onset of the rainy season under lower temperature are sensitive to rot but less susceptible to chilling (Schirra et al. 1999b). The rate of water loss increases during cold storage and the subsequent marketing period—and more rapidly so in summer than in autumn fruit, presumably because of a more rapid rate of metabolism resulting from the higher summertime temperatures (Monselise and Goren i987). The sharp increases in weight loss when fruits are moved from chilling to non-chilling temperatures have been related to microscopic cracks in the rind (Cohen et al. 1994), on which decay depends during the marketing period.
Keeping the fruits in ventilated cold rooms at 6 to 8°C and 90 to 95% relative humidity is generally recommended for a storage life of 3 to 4 weeks (Gorini et al. i993; Chessa and Barbera 1984; Cantwell 1995). This is the best compromise among preventing chilling injury, controlling decay, reducing respiration, and reducing transpiration. Upon longer storage, losses from rot and/or chilling injury may increase sharply, especially when the fruits are transferred from cold storage to the market. Chessa and Barbera
(1984) found an 84% decay of autumn 'Gialla' fruit after a 60-day storage at 8°C, dropping to 67% at 5°C. Decay was caused by Alternaria, Fusarium, and Penicillium spp., and, to a lesser extent, by bacterial infections. Storage under intermittent warming to 8°C for 4 days for every 10 days at 2°C reduces chilling injury and decay after 6 weeks of refrigeration followed by 1 week at 20°C compared to storage at a constant 6°C (Chessa and Schirra 1990). Storage at cycles of 3 weeks at 2°C followed by 1 week at 8°C halves decay compared to continuous storage at 5 or 8°C (Gorini et al. 1993).
Storage at 5°C under a controlled atmosphere of 2% O2 and 2% or 5% CO2 reduces fruit decay by approximately 77%, alleviates chilling injury, and decreases water loss, thus resulting in fruits of enhanced appearance compared to those in a standard atmosphere (Testoni and Eccher-Zerbini 1990). Packaging with heat-shrunk polyethylene film remarkably reduces fruit weight loss, alleviates chilling injury, and results in better appearance but does not reduce decay during 6 weeks of storage at 6°C and subsequent marketing at 20°C (Piga et al. 1996). Wrapping with polyolefinic film retains fruit freshness and greatly reduces fruit weight loss during 4 weeks of storage at 9°C and subsequent marketing (Piga et al. 1997).
Postharvest dip treatments with conventional fungicides, such as benomyl, captan, and vinclozolin, are ineffective in controlling postharvest decay of cactus pear fruit, although thiabendazole (TBZ) effectively suppresses decay development and mitigates expression of chilling injury (Gorini et al. 1993). Dip treatments (2 minutes) with a heated (48-50°C) mixture containing 250 mg/liter beno-myl and i050 mg/liter betran reduces decay during 8 weeks of storage at 0°C and 80 to 85% relative humidity (Berger et al. 1978). The increased efficacy of heated fungicides reflects enhanced fungicide uptake and better coverage (Cabras et al. 1999). Fruit dipping in 1 mg/liter TBZ at 55°C for 5 minutes significantly reduces cold- and rot-induced losses in late-crop fruits during 4 weeks of storage at 6°C followed by i week of marketing at 20°C, without causing heat injury or detrimental effects to fruit firmness, flavor, taste, or peel appearance (Schirra et al. 1996). Similar results are observed following dipping in hot water, which also helps remove glochids—known causes of numerous micro-lesions in the skin that represent possible entry points for wound pathogens.
Hot air treatment for 24 hours at 38°C and > 95% relative humidity reduces chilling injury (Schirra et al. 1996). For summer fruits, such a hot-air treatment reduces decay fourfold, whereas a 48- or 72-hour treatment prior to 3 weeks at 6°C and i week at 20°C halves the decay
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