Annona Species Monograph.pdf - Crops for the Future

Chapter 9. Genetic Improvement
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more than several hundred thousand seedlings over more than 100 years
(George et al., 1999), although some progress has recently been made in
selecting new cherimoya cultivars.
A very simple but interesting strategy, developed by members of the
California Cherimoya Association, is to bring samples of new cultivars to
show at their Annual Meeting. This helps to identify new materials that they
might want to grow next year (Grossberger, 1999). This strategy has a long
history in developed countries, such as the USA, and needs to be more
widely adopted in developing countries.
George et al. (1999) commented that a major Annona breeding programme,
funded by the Australian Custard Apple Growers Association, started with
the objective of developing high quality seedless cultivars of atemoya
(Annona squamosa x A. cherimoya hybrids). The vernacular name 'custard
apple' is usually and wrongly used to refer to Annona squamosa by Indian
researchers (Pawshe et al., 1997) and to Annona hybrids or to Annona
cherimola by UK and Commonwealth researchers (George and Nissen, 1987,
Van Damme and Scheldeman, 1999). Therefore, the reader is advised to
carefully identify the origin of articles in order to correctly identify the
species which is referred to.
In this breeding programme, the Australian breeders first produced
tetraploids, either through gamma irradiation or colchicine, and then crossed
these to diploids to produce seedless triploids. There are several other
potentially useful methods of obtaining seedlessness in annonas, e.g., a)
trying to identify progeny from diploid x diploid crosses with small seed
sizes and numbers; b) producing triploids from diploid x tetraploid and
tetraploid x diploid crossing, as done in Australia; c) producing triploids
through protoplast fusion of diploids and haploids; d) irradiation of budwood
to "knock out" genes for seed production; e) crossing of low-seeded parents
(as the seed number is an heritable character); f) development of selfincompatible
parthenocarpic hybrids; and g) using endosperm culture to get
triploids. Not all of these strategies are currently being employed in annona
breeding programmes (George et al., 1999).
Progeny of a cherimoya x sugar apple cross produced fruits which were late
maturing (spring in Queensland), and appeared to have inherited the
flowering and fruiting characteristics of atemoya, with flowering in autumn
and fruit maturity in late spring, under the subtropical conditions in that part
of Australia. A similar study was carried out by Zill Nursery near Boyton
Beach, Florida, and approximately 3,000 seedlings, mainly from interspecific