Protocols for Micropropagation of Woody Trees and Fruits

DATE PALM MICROPROPAGATION
Figure 5. Field transfer of in vitro-derived date palm plants. A) Formation of a true leaf
under greenhouse conditions. B) Plants after 1 year of transfer to field, C) The same field 1
after 4 years showing normal phenotype and vigorous growth.
2.6. Morphological and Molecular Analysis
The issue of genetic fidelity of date palm plantlets derived from tissue culture has
been a controversial subject. Some reports have suggested limited occurrence of
somaclonal variants among regenerants based on morphological characteristics and
DNA profile, while others observed no variability. Such differences in results could
be attributed to the mode of regeneration used, the length of the callus culture
maintenance period, the growth regulators augmented to the culture medium, as well
as genotypic differences.
Although changes in some of the morphological characteristics and growth parameters
of vegetative and fruit stages are visually obvious, correct cultivars identification
in date palm is usually not possible until fruit stage which manifests several
years after field transplanting. Furthermore, performance characteristics, such as
fertility, yield potential, fruit quality or disease susceptibility, are hidden in the
juvenile stage. This makes morphological characterization impractical and does not
allow either correct cultivar identification or early detection of off-type regenerants
at juvenile stage.
Since morphological identification of off-types is unreliable particularly at the
juvenile stage, molecular markers describe the internal make-up of a plant and
identify the variance based on either the composition of DNA or protein products
519