Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
GA is costly and not affordable for most resource-poor cherimoya growers,
especially in developing countries. Soaking in distilled water has shown a
significant effect on germination, although germination was less concentrated
and more irregular over time; nonetheless, it is a cheaper, though less
effective, alternative to GA treatment. Another alternative, which also
resulted in rapid and high germination of cherimoya seeds, is soaking for 48-
72 h in distilled water, or for a shorter time in hot water (92°C) and gradually
cooler water (de Smet et al., 1999). Wild soursop (A. senegalensis) produces
seedlings rapidly when the seeds are scarified (FAO, 1988).
In general, seedlings show variability in plant growth and fruit yield because
they are sexually propagated materials. However, soursop seedlings
cultivated in the Cerrado region of Brazil, which generally start flowering
and producing at the same age as grafted soursop trees, have similar fruit
yield and greater longevity (Pinto et al., 2001). In addition, some seed
propagated orchards are used as seed sources for the establishment of
rootstocks.
Seeding substrates, especially those with composts, may contain root rot
fungi, weed seeds and nematodes, to which most of the annonas species are
susceptible, and seedlings may not grow well in their presence. The pretreated
medium should be composed of fine river sand or a mixture of two
parts fine sand and one part garden soil (Coronel, 1994) or compost.
Therefore, pre-treatment of seeding compost is strongly recommended
(Torres and Sánchez, 1992; Junqueira et al., 1996; Kavati and Piza Jr., 1997).
Recommendations have included methyl chloride, chloropicrin and other
gaseous chemicals (Hartmann et al., 1990); more recently these chemical
treatments have been substituted, especially under tropical conditions, by a
less expensive and safer treatment called the 'solarization system'.
Solarization involves covering compost (thickness of the compost layer
should not exceed 30 cm) with a transparent plastic sheet, which allows solar
rays to penetrate the medium, thereby increasing the temperature high
enough (> 50°C) to kill most problematic soil microorganisms (Plate 2).
The treated substrate is transferred to the germination system used in the
nursery. The seeds can be sown directly in perforated black plastic bags (22
cm diameter, 25 cm length and 0.2 mm thick; Pinto and Silva, 1996) or can
be sown in seed boxes, seedbeds or other shallow containers, for later
transplanting to plastic bags when the seedlings are 8-15 cm tall (Torres and
Sánchez, 1992; Coronel, 1994; Agustín and Alviter, 1996; Fuentes, 1999).
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