Annona Species Monograph.pdf - Crops for the Future

Chapter 9. Genetic Improvement
a short period. Early maturity, better fruit appearance and long post-harvest
life for tropical annonas, and in the subtropics, greater cold tolerance, are
objectives for cherimoya breeding (Nakasone and Paull, 1998).
9.4.2 Breeding objectives
The first objective that the breeder has in mind is the determination of the
specific characteristics that are important for the new cultivar - the ideotype
(Table 9-1). These characteristics may help a breeder to select parental
groups to be used in an annona breeding programme, in order to obtain
desirable progenies. These progenies may not have all desirable
characteristics, but at least will have those most important to growers,
retailers and consumers. For instance, a sweet sugar apple cultivar with long
shelf life fruits (> 5 days), which is important from a consumer’s viewpoint,
may not be selected, if it presents low yield (< 20 kg/tree/year) and fruit
weight lower than 400 g (Table 9-1), since no grower will plant this cultivar.
Indeed, yield is always an important trait in cultivar development for any
crop species (Fehr, 1987 b) and annona is no exception. However, genetic
improvement for yield is the most difficult and expensive of all breeding
objectives, due to the complex nature of its inheritance and the numerous
environmental factors influencing the trait. The different yield responses of
the various Annona species and cultivars, such as soursop (Pinto and Silva,
1996) and cherimoya (Gardiazabal and Cano, 1999), in the same region,
prove the complexity of the genotype-environment interaction.
Quality is another important characteristic for the improvement of annonas,
as important or sometimes more so than yield, since market value is based on
the fruit's appearance and its organoleptic characteristics. A complicating
factor is that quality standards may not be the same for all markets. In
cherimoya, a skin without protuberances above the carpel walls may be
preferable, since this diminishes the susceptibility of the fruit to mechanical
damage (Gardiazabal and Cano, 1999). Small, sweet soursop fruits are
recommended for the fresh market, while large acid ones are more suitable
for the processing industry (Pinto and Silva, 1996). However, ripe fruits
become soft and perishable, with subsequent rapid fermentation. Besides the
difficulty to determine a correct harvest point, handling and processing
procedures have to be adapted to this postharvest problem. Therefore, it is
difficult to produce fresh soursop fruits for export to distant markets without
resolving this postharvest impediment.
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