Annona Species Monograph.pdf - Crops for the Future

Chapter 9. Genetic Improvement
preliminary study, using eleven isoenzyme loci, was developed with five
Annona species. Strangely, soursop, mountain soursop (A. montana), and
pond apple (A. glabra) presented no variation between or within the
populations studied.
Some isoenzymes studies with cherimoya have been carried out. Groups at
the University of California (USA) and University of Granada (Spain)
studied the variation in isoenzyme patterns of cherimoya cultivars from the
USA and Spain. Both groups found sufficient variation to distinguish
cultivars and to evaluate cherimoya germplasm (Ellstrand and Lee, 1987;
Pascual et al., 1993). This isoenzyme analysis is important, since cultivars
have been confused and are widely known by the wrong names. For instance,
there is often confusion with the cherimoya cultivar ‘McPherson’, which is
incorrectly identified in Spain (Grossberger, 1999).
In Mexico, Medina et al. (1999) used molecular biological techniques to
select soursop varieties according to their resistance to fungal diseases. They
analysed the electrophoretic pattern of peroxidase isozymes and observed the
variation between isoforms of healthy and infected plants. Since these
diseases are detrimental to soursop production, the researchers consider these
isoenzyme patterns as markers to select healthy and infected individuals, and
potentially to identify resistant and susceptible genotypes.
Isoenzyme studies are limited because they are carried out using a relatively
small number of loci. RAPDs offer an enormous number of markers covering
the whole genome, and is a more powerful technique for genotype
identification and germplasm evaluation. Ronning et al. (1995) estimated
variation between cherimoya, sugar apple and atemoya, and determined the
inheritance of these markers in the F1. All fifteen primers used generated
repeatable polymorphic patterns, resulting in a very efficient method to
distinguish genotypes of Annona species.
In short, the recent biotechnological studies, both cellular and molecular,
have shown great potential to further annona development, not only to solve
problems of mass propagation of superior cultivars, through
micropropagation techniques, but also to identify or fingerprint annona
cultivars, as well as to determine cultivar parentage, through RAPD markers.
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