Annona Species Monograph.pdf - Crops for the Future

Chapter 9. Genetic Improvement
and seedlings of cherimoya, but sugar apple and soursop are reputed to be
less variable (George and Nissen, 1992; Pinto and Silva, 1996).
The influence of Annona rootstocks on scion behaviour is also quite marked,
and genetic variability within seedling rootstock lines and between different
rootstock species induces wide variability in scion performance (Page, 1984).
This kind of genotype and environment interaction requires much more study
than it has received to date.
Seedling populations of some Annona species, such as sugar apple and
soursop, are known to be rather uniform (George and Nissen, 1987). There
are some growers using seedlings in commercial orchards in Brazil (Pinto
and Ramos, 1999). Since annonas are considered out-crossing species
(George and Nissen, 1987; Scheldeman, 2002) with high degrees of
heterozygosity and do not generally produce true-to-type seedlings,
commercial orchards should be clonally propagated to avoid possible
influence of genetic variability. However, little has been done to identify and
characterize the diversity in any of the Annona species.
9.3 Characteristics of annona ideotypes
There are several characters that are considered important in a superior
commercial cultivar of an Annona species (Table 9-1). According to
Mahdeem (1990), the most important characteristics of an ideotype,
especially of cherimoya, are the following: a) vigorous and prolific plants,
compatible with one or more rootstocks, regular-bearing, resistant to cold and
dry conditions, as well as to pests and diseases; b) architecture of the canopy
with acceptable form, which does not need pruning, and which is easy to
harvest; c) abundant flowers with fertile pollen, and which attract insect
pollinators; d) out-of-season fruit harvest for specific locations; e) fruit with
symmetrical form, high natural fruit set, hard skin resistant to pests and
diseases, as well as with long post-harvest life; f) excellent fruit quality with
regards to flavour, with fine, fibreless and firm pulp texture, and a low
number of free seeds in the pulp. Each species will have a slightly different
ideal type, due to their inherent biological differences.
9.4 Breeding programme
Wester (1913) was the first scientist to realize the possibilities for genetic
improvement of annonas and initiated breeding programmes in Florida and in
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