Annona Species Monograph.pdf - Crops for the Future

Chapter 8. Genetic Resources
F. R. Ferreira and A. C. de Q. Pinto
8.1 The annona genepool
Annona species are widely distributed and their genetic resource
conservation has achieved a degree of world-wide attention. Until recently,
the centres of diversity of Annona seemed to contain inexhaustible supplies
of genetic materials for plant breeding. However, these genetic materials
have been changing rapidly as a result of genetic erosion in both cultivated
and wild annonas. Human pressure on natural ecological systems, leading to
the destruction of wild species, and the introduction of improved new clonal
varieties, which have replaced many landraces, has promoted the loss of the
genetic variability that had accumulated over a period of thousands of years
of natural evolution and human directed domestication (Ng, 1991).
Chromosome numbers among Annona species do not vary significantly.
Kessler (1993, cited by Scheldeman, 2002), reported that most of the Annona
species present a chromosome number of 2n = 2x = 14 or 16, except for A.
glabra which is a tetraploid species.
The most important cultivated Annona species not treated in this book
include: ilama or annona blanca (A. diversifolia Saff.) from Central America
and Mexico; pond apple or alligator apple (A. glabra L.) from Tropical
America and West Africa, cultivated as a medicinal plant rather than a fruit
(Scheldeman, 2002). This author also mentioned mountain soursop or
cimarrona (A. montana Macfad), soncoya or negro head (A. purpurea Moc.
et Sessé), and posh té or cawesh (A. scleroderma Saff.), all three of which are
from Central America. A. diversifolia, A. montana and A. muricata are quite
similar morphologically, and they can be cross-grafted with reasonable
compatibility. Along with the cross-fertility of A. cherimola and A. squamosa
there are clearly many aspects of species relationships that are by no means
well studied yet (George et al., 1999).
There are very extensive areas in which diversity of numerous species has
been observed (Table 8.1), which suggests that certain specific regions need
targeted exploration. These include the mid-elevation valleys of the Andes,
many parts of Brazil, Mexico, Guatemala, Honduras and the Antilles.
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