Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 89

Breeding programmes are few and have been mainly focused on cherimoya and atemoya and, to a lesser extent, pawpaw. The most important breeding objectives are related to fruit diseases, fruit quality (°Brix and acidity) and postharvest handling. The thin skin of cherimoya fruit is very susceptible to the Mediterranean fruit fly, Ceratitis capitata and to other fruit flies, i.e. those of the genus Anastrepha. The skin can also be easily damaged during transport and, consequently, skin resistance, evaluated as resistance with a penetrometer, is an important fruit trait in breeding programmes.

The flavour of the cherimoya fruit has been described as a mixture of banana and pineapple or strawberry and pear (Schmidt, 1971), and to obtain a good fruit quality with this flavour, the pulp with °Brix >20 is considered optimal. Another important trait is to minimize the number of seeds or to develop fully seedless cultivars (Lora et al., 2011b).

Fruits of Annona and Asimina species are climacteric with rapid ripening and are sensitive to chilling (Pareek et al., 2011). Atemoya (Brown et al., 1988), cherimoya (Palma et al., 1993) and pawpaw (Archbold and Pomper, 2003) can generally retain good fruit quality after 4–6 days at 20–25°C. Cultivars with longer postharvest life are important traits in breeding programmes. Low temperature storage is generally used to extend postharvest storage (Pareek et al., 2011). Cherimoya and atemoya fruits can be stored for 15–20 and 9 days, respectively, at 8–10°C, but below 8°C they can suffer cold damage (Palma et al., 1993; Farré et al., 1999; Pareek et al., 2011). Pawpaw fruits, a species adapted to cold temperatures, can be stored at 4°C for 28 days (Archbold and Pomper, 2003). Chemical treatments involving 1-methylcyclopropene or CaCl₂ and coating cherimoya fruit with wax have been used to prolong postharvest storage (Pareek et al., 2011).

Cultivars with high productivity are also important for cherimoya, atemoya and pawpaw. Cherimoya and atemoya production could also be improved significantly by utilizing optimal hand pollination and through the use of a second pruning at the end of the first blooming season to cause more flowering under Mediterranean conditions (Farré et al., 1999).

In a review of pawpaw breeding and selection, Peterson (2003) identified vigour, yield and diverse fruit quality traits, e.g. larger fruit size, smaller and fewer seeds, appearance, uniformity of fruit and mild, sweet flavour with lack of unpleasant aftertaste and a longer shelf life as primary breeding targets.