Annona Species Monograph.pdf - Crops for the Future

Chapter 9. Genetic Improvement
9.5 Role of modern biotechnology
9.5.1 Tissue culture
Tissue culture has many uses: a) micropropagation; b) maintenance of
germplasm collections; c) embryo rescue; d) development of haploid plants;
e) enhancement of variability by somaclonal variation; and f) to prepare
explants for transformation methods (Encina et al., 1999; Herrera, 1999).
However, for most annona work the main objective is micropropagation, as
the conventional methods of propagation are slow and costly, and in some
cases, such as with cherimoya, are also inefficient. This appears to be
because the morphological potential for rooting of cherimoya is very low
(Encina et al., 1999).
Researchers have successfully micropropagated cherimoya, sugar apple,
soursop and atemoya. Atemoya clonal propagation was described by Rasai et
al. (1994). They obtained multiple shoot formation from hypocotyls and
nodal cuttings of the cultivar ‘African Pride’. The explants were cultivated in
MS medium supplemented with BAP, kinetin, biotin and calcium
pantothenate. In spite of improved rooting by shoot pre-treatment in liquid
MS medium containing IBA, the percentage of rooting was still low (40%)
and remains a limiting factor for commercial micropropagation of atemoya.
Benjoy and Hariharam (1992) described plantlet differentiation in soursop.
They found a mean of 4.8 shoots per hypocotyl explant growing in an MS
medium containing BAP and NAA. However, they reported only relative
success in rooting and survival (35%). To improve the system, Lemos and
Baker (1998) suggested the use of sorbitol to induce de novo shoot
development and Lemos and Blake (1996 c) tried galactose and NAA to
stimulate rooting. Nonetheless, no commercial protocol is ready for use.
The first haploid plants induced by anther culture in fruit trees were reported
by Nair et al. (1983) with sugar apple. The availability of haploids is very
important for fruit-breeding, because of the long generation intervals, the
highly heterozygous nature of most fruit species and the presence of
parthenocarpy and self-incompatibility. These researchers obtained callus
differentiation, and formation of triploid roots and shoots from sugar apple
endosperm (Nair et al., 1986). Their aim was development of seedless fruits,
but a complete plantlet was not obtained.
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