DESCRIPTION OF THE CACTUS PEAR
I. Chessa, G. Nieddu - Dipartimento di Economia e Sistemi Arborei, Università di Sassari - Italy
BOTANICAL SPECIES: Opuntia spp.
HABITAT. The ancestral species originated in tropical America but the greatest genetic diversity in the species of the genus Opuntia is found in the semiarid Mexican plateaus. The cactus pear grows in all parts of the American continent, from southern Canada to Patagonia, and in the course of time has been cultivated in different areas of Europe, particularly the Mediterranean countries, as well as in Africa and Australia. Thanks to its ability to adapt to different environmental conditions, the cactus pear grows in plains, coastal regions, plateaus and among diverse vegetation. A common feature of the areas where the plant grows is a more or less marked degree of aridity to which the plant has adapted thanks to its CAM photosynthetic metabolism.
Low winter temperatures (from -6 to -8°C) reduce the yield of the cultivated plants but have no effect on the wild species. Suitable soil for cultivation is about 20-40 deep, of medium texture and with a pH value of between 5.0 and 7.5.
PLANT. The plant is arborescent and can reach a height of m 3-5. Its aerial portion consists of flat green, wax-covered internodes (cladodes), usually obovate and of a size ranging between 30-60 cm long, 20-40 cm wide and 19-28 mm thick. The cone-shaped leaves, only a few millimetres long, which are present on the cladodes or floral axis up to flowering, are short-lived, having a duration of about 30 days. At the leaf base are found the areolas, modified axillary buds, the number of which per cladode is usually constant (in Opuntia ficus indica 8-9 series in a spiral arrangement). They have spines and glochids on them and evolve into roots, cladodes or flowers. The true spines, absent in species like O. ficus-indica, are sclerenchymatous and of different lengths and colours. The glochids, which are usually present, are deciduous since they are not sclerenchymatous at the base. These are generally yellow, thin, a few millimetres long. The basal cladodes tend to lignify until a well-defined trunk is formed. The root system is not far below ground but in wild plants appears very extensive.
FLOWERS. These are mainly distinguished from the areolas arranged along the upper margin of the corona of 1-year-old cladodes. They are hermaphrodites, with a calyx and corolla of barely visible sepals and conspicuous petals of different colours, most often orange-yellow. The pericarp is 2-2.5 times longer than the perianth and is tuberculated with about 8 series of spiral areolas. Numerous stamens surround the gynoecium which is a pistil surmounted by a multiple stigma. The ovary is inferior, unilocular, containing several ovules in laminal placentation. In Mediterranean countries and in cultivated plants, flowering occurs in May and June. Anthesis ends after a very short period, ranging from 24 h (in dry regions of Mexico) to 36-48 h (in plants cultivated in Sicily and Sardinia). Self-pollination and cross-pollination can co-exist and several species are characterized by pre-anthesis cleistogamy, as the stigma can be receptive before the flower opens.
FRUIT. The fruit is a fleshy, polyspermic unilocular berry. The flesh is formed from the papillary cells of the dorsal epidermis of the funicular involucre and the funicle while the epicarp derives from the receptacle, the vegetative tissue surrounding the ovary. The fruit of the different species and biotypes shows great variability in shape, size, colour and quality. The seeds are numerous (from about 100 to over 400 per fruit), disciform, about 3-4 mm in diameter. Anomalies are often seen in the fruit. It grows and increases in fresh weight in a double sigmoid curve. Its nutritional value lies essentially in its glucose and fructose content (6-8%); the level of ascorbic acid is moderate (23mg 100-1g); acidity is low (0.06%).
VARIETIES. Many different species of Opuntia are grown in Mexico for fruit production whereas in Italy and the Mediterranean region in general, Opuntia ficus-indica is cultivated. The lack of a well defined standard for varieties has led to clonal populations being developed in producer countries, mostly distinguished on the basis of some morphological features of the fruit and cladodes. Thus, in Italy and Spain three main varieties have been produced, the colour of the fruit determining the denomination. In South Africa varieties with cladodes of different shapes can be found while in Chile the most common variety has fruit which is green even when ripe. Other characteristics (vegetative vigour, sugar and protein content, cladode fibre, etc.) determine how the variety can be utilized.
USE. The cactus pear can be used in many ways in diverse sectors, utilizing different parts of the plant. In the food sector, besides consumption of the fresh fruit, jams, alcoholic and soft drinks, syrups, candied fruit and flour can be produced from the plant and oil extracted from the seeds. The young cladodes are eaten as a vegetable (only in Mexico) or made into other products. For cattle feed, it is mostly used fresh, but it can also be ensiled so as to utilize cuttings from processes using the plant in other ways. The different parts of the plant are also used in industry (dyes, mucilage, pectins, organic fertilizer, biogas), in the pharmaceutical sector (in the treatment of diabetes, obesity, inflammation, etc) and in the cosmetics industry. In addition, Opuntiae are used as ornamental plants.