A set of 16 expressed sequence tag (EST)-derived simple sequence repeat (SSR) and 15 EST-derived single nucleotide polymorphism (SNP) markers together with 4 amplified fragment length polymorphism (AFLP) primer combinations were analyzed on 43 wild (Hordeum vulgare ssp. spontaneum -HS), 35 cultivated (H. vulgare ssp. vulgare -HV) and 12 elite (H. vulgare ssp. vulgare -from EU) barley lines. SSR markers were found most polymorphic with an average PIC value of 0.593 and eight alleles per marker, while AFLP markers showed the highest effective multiplex ratio (26.4) and marker index (5.042). The effective marker index (EMI) was recorded highest (0.468) for AFLP markers and lowest (0.341) for the SNP markers while the SSR markers had an intermediate EMI (0.442). Cluster analysis on combined set of SSR, SNP and AFLP genotyping data classified wild, cultivated and elite barley lines in three distinct groups. The present study suggests the SNP markers as the best class of markers for characterizing and conserving the genebank materials and the AFLP and SSR markers more suitable for diversity analysis and fingerprinting. #

Genetic variation present in wild and cultivated barley populations was investigated using two sources of microsatellite also known as simple sequence repeat (SSR) markers. EST-SSRs are derived from expressed sequences and genomic SSRs are isolated from genomic DNA. Genomic SSR markers detected a higher level of polymorphism than those derived from ESTs. Polymorphism information content was higher in genomic SSRs than EST-derived SSRs. This study showed that the EST-SSR markers developed in cultivated barley are polymorphic in wild and cultivated varieties and produced high quality markers. Ten of these functional markers were polymorphic across the accessions studied. EST markers indicated clearer separation between wild and cultivated barley than genomic SSRs. The EST-SSRs are a valuable source of new polymorphic markers and should be highly applicable to barley genetic resources, providing a direct estimate of functional biodiversity.

Intra- and inter-specific genetic variation was investigated in seven diploid Aegilops species using the amplified fragment length polymorphism (AFLP) technique. Of the seven species, the cross-pollinating Aegilops speltoides and Aegilops mutica showed high levels of intraspecific variation whereas the remaining five self-pollinating species showed low levels. Aegilops bicornis, Aegilops searsii and Ae. speltoides formed one cluster in the dendrograms, while Aegilops caudata and Aegilops umbellulata formed another. Relationships among the species inferred were more consistent with the relationships inferred from studies of chromosome pairing in interspecific hybrids, and previous molecular phylogenetic reconstructions based on nuclear DNA, than they were with those based on molecular plasmon analysis, suggesting that the nuclear genome has evolved differently from the cytoplasmic genome in the genus Aegilops.

Genetic diversity in five wild types of wheat was estimated using Simpson's index (based on heterozygosity) applied to data from AFLP markers. For such studies, the cost of obtaining the required information increases both with the number of samples required to estimate diversity and with the number of markers used. When the population studied is in Hardy-Weinberg equilibrium (HWE), allelic frequencies follow the binomial expansion and parametric methods can be used to calculate the variance of the diversity index in terms of the number of individuals sampled. Inbred species are never in HWE. With regard to such populations, this study addresses the question of the sample size required to estimate gene diversity using a distribution-free re-sampling method. We studied populations of five wild species (Aegilops speltoides, Triticum urartu, Triticum boeoticum, Triticum dicoccoides, and Triticum araraticum) as sources of diversity. We used bootstrap re-sampling with varying sample sizes to develop a relationship between the precision of the diversity estimate and the sample size. Such a relationship was used to determine the samples required for capturing a given amount of diversity and its precision. We found that 5-6 samples are sufficient to obtain a standard error equal to 10% of the diversity in the populations of the species Ae. speltoides, T. dicoccoides and T. araraticum. However, more than 12 samples would be needed for populations of T. urartu and T. boeoticum. The procedure presented here can be used to obtain the optimum sample size for other crop species as well.

Mutants of Phytophthora parasitica Dast. more or less resistant to dimethomorph or metalaxyl were obtained by treating mycelium with ultraviolet radiation. Some metalaxyl‐resistant mutants exhibited levels of resistance (i.e. the ratio between the EC50 values for the mutant and the wild‐type strain) greater than 100, but those observed in the dimethomorph‐resistant mutants never exceeded 25. Most mutants retained their resistance after sub‐culturing on unamended agar medium. Single zoospore clones derived from a metalaxyl‐resistant and a dimethomorph‐resistant mutant, selected as amongst the most resistant, had levels of resistance similar to those of the parental strains. The metalaxyl‐resistant mutants were also resistant to the related phenylamide fungicides, furalaxyl and benalaxyl, but remained sensitive to dimethomorph. The dimethomorph‐resistant mutants were not resistant to phenylamide fungicides. The pathogenicity of some metalaxyl‐ or dimethomorph‐resistant mutants on tobacco leaves was similar to that of the wild‐type strains.

No abstract

Durum wheat [Triticum turgidum L. subsp. turgidum convar. durum (Desf.) MK] is an important cereal crop economically and nutritionally in the Central Asia and Caucasian, West Asia, and North Africa (CWANA) regions. Durum landraces and improved lines are largely grown in this region. Its genetic diversity has been studied using different molecular markers. The increasing availability of expressed sequence tags (ESTs) in wheat (Triticum aestivum) and related cereals provides a valuable resource of non-anonymous DNA markers to study durum diversity. In this study, a set of 517,319 Triticum aestivum EST sequences was employed for the identification of wheat simple sequence repeats called microsatellites (W-eSSRs) with the help of a PERL5 script called MISA. In comparison, barley microsatellites (B-eSSRs) have been used to exploit their transferability to durum wheat. Newly developed W-eSSR markers were probed on the 115 recombinant inbred lines (RIL) of the International Triticeae Mapping Initiative (ITMI) population (Opata 85 9 Synthetic 7984). The polymorphic eSSRs were mapped. To examine the potential of the two types of eSSRs markers, 12 W-eSSR markers and 13 B-eSSR markers were used to fingerprint 153 wheat genotypes. Our results indicate that: (1) BeSSRs show a high level of transferability to wheat, (2) the developed W-eSSRs are significantly polymorphic than those derived from genomic regions, (3) new W-eSSRs were identified and integrated in the ITMI genetic linkage map and, (4) B-eSSR and W-eSSRs are providing additional markers for comparative mapping following gene introgressions from wild species and carrying out evolutionary studies.

Pistachio (Pistacia vera L.) is a strategic nut tree species in the Middle East which holds comparative advantage over other fruit trees in view of its hardiness, income generation opportunities and benefits for the ecosystem. Yet pistachio cultivation depends on a very narrow genetic base, in spite of the existence of many varieties still marginally exploited. Syria is an important center of diversity for pistachio. A country wide ecogeographic survey in this country was carried out to determine the extent of pistachio genetic diversity and its use. As a whole, 114 accessions were collected from 37 farms to assess diversity at morphological and molecular level. Molecular evaluation was carried out using Amplified Fragment Length Polymorphism (AFLP) technique and performed using seven primer pair combinations. Results from the studies allowed the identification of 25 pistachio female varieties in Syria, some of which unique and described for the first time. Three groups of pistachio diversity were identified by cluster analysis which provides useful information about the distribution of genetic diversity in Syria for enhanced use and sustainable conservation.