Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
Brown rot (Rhizopus stolonifer) is another serious disease which attacks the
fruits, generally at harvest and during post-harvest periods (Pinto and Silva,
1996; Rebollar-Alviter et al., 1997) - (Plate 7). The main contributing factors
for a higher incidence of brown rot are high RH in the orchard and some kind
of physical damage to the fruit (Torres and Sánchez, 1992). Perforations by
wasps (soursop seed borers) on the fruit peduncles are probably one of the
entry points for fungal establishment, the attack of which promotes a brown
rot and later mummification of the pulp (Torres and Sánchez, 1992; SPT-
TCA, 1999). A preventive control measure is the elimination of seed borer
attacks or other physical damage of fruits, as well as removal of damaged
fruits on the ground (Torres and Sánchez, 1992).
Like many other tropical fruits, post-harvest rotting is largely responsible for
the short shelf life of annona fruits and experimental studies have evaluated
possible solutions to this problem. George et al. (1987) recommended
dipping annona fruits in either a heated benomyl suspension with 0.5 g a.i./l
(or the same concentration guazatine solution) at 50° to 52°C for 5 minutes
for post-harvest control of rots. Dipping the annona fruits in unheated
prochloraz (0.125 g a.i. per litre) for 1 minute at 25°C also provided a good
control of post-harvest rotting. However, some treatments, particularly
prochloraz, can induce skin injury at high concentrations, and should be
avoided.
Minor diseases can also be important in some countries or regions (Table
10.14). Some fungi causing minor diseases develop and attack more severely
under high relative humidity and hot temperatures. Two soursop diseases
commonly called 'burning string' (Corticium koleroga) and 'zoned spot'
(Sclerotium coffeicolum) are examples of these kinds of fungi. In Mexico,
blight and black scab are also important diseases and the former can even
show incidences of up to 80% on cherimoya leaves in the high humidity
period of the year (Nava-Díaz et al., 2000). Fumagina (Stigmella spp.) is a
cosmopolitan fungus whose attack is aided by certain species of ants,
although this disease is described as having one of the lowest incidences
(28.5%) in Mexico (Nava-Díaz et al., 2000). Rubelose (Corticum
salmonicolor) and cercosporiose (Cercospora annonae) are common
diseases on twigs and leaves of soursop, although predisposing
environmental conditions and symptoms are different. Symptoms of rubelose
are yellowish pink mycelium on the trunk followed by exudation of latex,
whereas cercosporiose symptoms are distinguished by development of black
circular lesions on the leaves. The former disease occurs under the high
humidity and hot temperatures occurring in the Amazon region and in some
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