Genetic Variation in Date Palms Propagated from Offshoots and Tissue Culture

Date palm (Phoenix dactylifera L.) is a major tree crop in arid regions of the Middle East and North Africa, having an important impact on the economy of many countries in these regions. Date palms are traditionally propagated through offshoots. The development of propagation methods through tissue culture resulted in massive expansion of date palm plantations. While most trees generated from tissue culture are normal and true-to-type, several typical abnormal phenotypes are detected. The present study applies amplification fragment length polymorphism (AFLP) analysis to characterize the genetic variation of two elite date cultivars, `Barhee' and `Medjool', as well as male clones, propagated from offshoots and through tissue culture. The two cultivars have very distinct AFLP band patterns. Most offshoots, as well as the tissue culture-propagated plants, have very similar band patterns, demonstrating a low level of genetic variation. However, a significant level of genetic variation was detected among `Medjool' plants generated from tissue culture. Several phenotypically abnormal trees were characterized by unique and different AFLP band patterns. The male clones are characterized by a high level of polymorphic bands. Genetic variation was also detected between various tissues of variegated `Medjool' trees propagated from tissue culture. The significance of these results, regarding the mechanism of the phenomenon and its relevance to agricultural practice, is discussed.

Polyploidization-induced genome variation in triticale

Polyploidization-induced genome variation in triticale (× Triticosecale Wittmack) was investigated using both AFLP and RFLP analyses. The AFLP analyses were implemented with both EcoRI–MseI (E–M) and PstI–MseI (P–M) primer combinations, which, because of their relative differences in sensitivity to cytosine methylation, primarily amplify repetitive and low-copy sequences, respectively. The results showed that the genomic sequences in triticale involved a great degree of variation including both repetitive and low-copy sequences. The frequency of losing parental bands was much higher than the frequency of gaining novel bands, suggesting that sequence elimination might be a major force causing genome variation in triticale. In all cases, variation in E–M primer-amplified parental bands was more frequent in triticale than that using P–M primers, suggesting that repetitive sequences were more involved in variation than low-copy sequences. The data also showed that the wheat (Triticum spp.) genomes were relatively highly conserved in triticales, especially in octoploid triticales, whereas the rye (Secale cereale L.) genome consistently demonstrated a very high level of genomic sequence variation (68%–72%) regardless of the triticale ploidy levels or primers used. In addition, when a parental AFLP band was present in both wheat and rye, the tendency of the AFLP band to be present in triticale was much higher than when it was present in only one of the progenitors. Furthermore, the cDNA-probed RFLP analyses showed that over 97% of the wheat coding sequences were maintained in triticale, whereas only about 61.6% of the rye coding sequences were maintained, suggesting that the rye genome variation in triticale also involved a high degree of rye coding sequence changes. The data also suggested that concerted evolution might occur in the genomic sequences of triticale. In addition, the observed genome variation in wheat–rye addition lines was similar to that in triticale, suggesting that wheat–rye addition lines can be used to thoroughly study the genome evolution of polyploid triticale.Key words: wheat, rye, polyploid, genome evolution, sequence elimination.

Analysis of diversity of natural populations and commercial lines of Echinacea using AFLP

An analysis of diversity of Echinacea native to North America, using amplified fragment length polymorphism (AFLP®), was carried out to complement a previously undertaken taxonomic revision of Echinacea that employed multivariate morphometrics. A total of 53 940 AFLP fragments, of which 40 455 were polymorphic, were scored on 435 individual plants from 58 populations consisting of ±10 individuals per population. The resulting polymorphism was sufficient to distinguish each plant. A monomorphic AFLP band and a polymorphic AFLP band that migrated at the same position, taken from samples of four species and eight varieties, were cloned, and multiple clones were sequenced. The polymorphic band at the same position across fragments was not identical, with identity as low as 23% compared with 50% identity of the monomorphic band, both of which were at the 100% threshold of sequence similarity. Thus, the AFLP banding profiles, irrespective of their sequence identity, were treated as phenotypes for population genetic, discriminant, and phylogenetic analyses. Variance components within populations and among populations within species were of equal magnitude, but the partitioned variation was slightly higher among varieties than among populations within varieties. Since no species-specific or variety-specific AFLP fingerprints were found, canonical discriminant analysis was conducted, resulting in support for four species but not for the varieties. Similar results were obtained with cluster and principal coordinate analyses, based on genetic distances. To achieve identification using AFLP fingerprints, various classificatory analyses were performed, followed by bootstrapping for validation. An example to identify an unknown plant at the species level with a minimum of 10 AFLP fragments, with greater than 82% overall correct classification, is provided. Phylogenetic analysis of all 435 individuals supported only Echinacea purpurea (L.) Moench and Echinacea laevigata (C.L. Boynton & Beadle) as separate entities, and only the three Echinacea atrorubens varieties and Echinacea pallida var. tennesseensis (Beadle) Binns, B.R. Baum & Arnason.Key words: Echinacea, population genetic analysis, multivariate analysis, AFLP band homologies.