Sweet orange (Citrus sinensis (L.) Osbeck.) Is the most cultivated citrus in the world. It is native to Vietnam, India and southern China. The trees have a compact, symmetrical and rounded crown and can reach 8-10 meters in height.
The sprigs, on some cultivars, can be thorny. The leaves, ovate, shiny and leathery, have a slightly winged petiole.
The flowers (orange blossom) are white and fragrant; they can be single or grouped in groups of up to six per inflorescence. Flowering is spring, while the fruits ripen in the autumn or the following winter; in some cases the fruits of the previous year may still be on the plant during the next flowering.
The fruits of the sweet orange do not ripen after the harvest: they must therefore be left on the plant until the desired degree of ripeness.
In tropical areas the fruits remain green, and to make them take on the orange color they are treated with ethylene, a gas that is also a hormone that intervenes in their maturation.
It resists drought well enough, but requires abundant watering for maximum production.
It is grafted on bitter orange, Volkamerian lemon and trifoliate orange (especially for plants in pots and in areas with low winter temperatures).
Orange flowers - Zagare
Sweet orange (Navel group variety) (website photo)
The varieties of sweet orange can be classified according to various parameters:
- ripening period: from the very early ones (ripen until mid-November; eg Navelina, Skaggs Bonanza), to the very late ones (ripen until the end of May and beyond; eg Valencia Late);
- internal coloring of the fruits: with blond pulp (eg. Ovale, Valencia Late, Belladonna) or pigmented (eg. Moro, Tarocco, Sanguinello, Sanguinello Moscato);
- acid content;
- presence of the navel or navel: the presence of the navel is due to a phenomenon of syncarpia, that is, from the formation of a second fruit, deriving from a second whorl of carpels; es. Washington Navel, Navelina, Thompson, Navelate, Golden Buckeye.
Diseases, pests and adversities
Green aphid of citrus fruits (Aphis citricola) attacks above all orange, mandarin and clementines, causing leaf curls, vegetative deterioration, flower pouring, drop of newly attached fruit and hindering the development of the shoots. Particularly harmful in nurseries on farmed plants, on reinnested plants. Cotton aphid infests mainly oranges, mandarins, clementines, causing limited damage. Brown citrus aphid causes docciatura and deformation of the leaves, without showy curling.
Mediterranean fruit fly (Ceratitis capitata). The most affected species are orange, clementine, mandarin. The damage is related to the oviposition stings which on the green fruits cause yellowish, rounded areas, on those in the ripening phase they have a greenish margin and are subject to drop.
Fillominatrice (Phyllocnistis citrella). The period in which the greatest infestations occur are early summer-autumn. Mines cause abnormal growth, crumpling, drying out, leaf fall.
Cotonello of citrus fruits (Planococcus citri). It mainly haunts lemon, orange, mandarin. The cochineal lives in colonies that are located in the points of contact between the various organs (fruits, leaves, etc.), in the most sheltered parts, in the shade. It is located on the peduncle of the fruit causing its drop.
Mites: Red weaver spider (Tetranychus urticae); Panonic or Red spider of citrus fruits (Panonychus citri) Rusty mite (Aculops pelekassi) Silver mite (Polyphagotarsonemus latus): they damage the leaves and the fruits.
Bacterial gums (mushroom - Phytophtora spp.). The characteristic symptom is the presence on the base of the trunk of a wet spot on the bark which then tends to crack with the escape of gummy exudates. On the aerial part there is a general deterioration with diffuse chlorosis, leaf fall, poor flowering.
Badly dried citrus fruit (mushroom - Phoma tracheiphila): Lemon, cedar and bergamot are the most sensitive species. The first symptoms appear on the apical leaves which show discolorations and yellowing especially in correspondence of the ribs. Over time, the leaves fall and the twigs dry out; in the case of infections of the epigean part, the course of the disease is slow and many suckers are released. On the other hand, if the infection starts from the roots, the plant dies quickly. Another symptom is the typical salmon color that the infected wood assumes.