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ISHS Acta Horticulturae 882: IV International Date Palm Conference

ON THE STATUS OF CHROMOSOMES OF THE DATE PALM (PHOENIX DACTYLIFERA L.)

Authors:   B. Al-Ani, A. Zaid, H. Shabana
DOI:   10.17660/ActaHortic.2010.882.28
Abstract:
The present article summarizes the status of the existing data on the issue of chromosome number and karyotype studies of the date palm, Phoenix dactylifera L. The literature on this subject is rather heterogeneous and confusing, and the number of chromosomes reported ranged from 2n=26 to 2n=36, in addition to the possible occurrence of polyploidy and aneuploidy. As early as 1910 Nemec examined young embryos of P. dactylifera and reported the presence of 2n=28 chromosomes. Beal (1937), however, observed 18 pairs of chromosomes (18 bivalents) as seen in M1 in the microsporocytes of 5 male cultivars of date palm; and 2n=36 chromosomes in root tips of 6 varieties of both male and female plants. Beal also observed in 2 other species of the genus Phoenix 1n=18 in P. canariensis and P. sylvastris; and 2n=36 chromosomes in 3 other species of the genus.
Selbi (1988) in his analysis of the chromosome karyotypes of both male and female date palms, indicated an identical chromosome number for both; and he reported 2n=36. Loutfi (1989) in his study on tissue culture-derived date palm plants obtained from inflorescence culture, found that the plants produced were morphologically identical to plants produced via organogenesis, and the chromosome number for these plants were strictly diploid. Ibrahim et al. (1998) also reported 2n=36 in some cultivars of date palm. Surprisingly, however, a chromosome number of 2n=26 was observed in two Moroccan date palm cultivars in the in vitro generated plantlets (Loutfi, 1999). The establishment of a date palm genomic map is important; and cytogenetic studies to firmly establish the chromosome number, and to detect chromosomal aberrations; expansion of date palm Gene Bank and biodiversity management using molecular tools, also represent important goals. The application of in situ hybridization, fluorescent in situ hybridization (FISH), spectral karyotyping (SKY) and other techniques to identify the chromosomes and karyotype, and to detect chromosomal aberrations and clonal variations; and early detection of gender in seedlings resulting from seed germination, should also not be ruled out. Although Sijak-Yakovlov et al. (1996) have detected the presence of sex chromosomes carrying distinctive nucleolar heterochromatins, based on chromomycin staining, nevertheless, a rather simpler tool for early detection of gender in date palm is of great importance. As early as the 1980's we have recognized an early disjunction of one pair of the 18 bivalents in some male cultivars of date palm during microsporogenesis at early A1 of the first meiotic division (Al-Ani and Nawal Abdullah, 1987); and through personal communication (Al-Mayiah et al., 2009) counted 2n=36 in some date palm cultivars, and detected the presence of sex chromosomes. Furthermore, they have detected some polyploidy and aneuploidy during their cytological investigation. Finally, the date palm whose seeds stand tolerant and totipotent; and maintained its true-to-typeness over a period of more than 2000 years, deserves more effort from biologists and other scientists to solve some cytogenetical problems associated with this socio-economically important crop, the ‘blessed tree’. It is suggested that some of these investigations may be a partial fulfillment of getting a higher degree at UAEU.

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