Aladdin Hamwieh

New microsatellite markers for assessment of genetic diversity in date palm (Phoenix dactylifera L.)

New primer pairs of genomic DNA microsatellite markers were tested to assess the genetic diversity of eleven date palm genotypes. The results indicated that out of thirty, only seven primers (23.3%) failed to amplify the expected PCR fragments, while thirteen primers (43.3%) amplified monomorphic banding patterns and the remaining ten primers (33.4%) generated polymorphic banding patterns. A total of 77 alleles have been observed with a mean of 7.7 alleles per locus. The average of gene diversity was 0.80 ranging from 0.6 (in marker DP168) to 0.9 (in two markers DP157 and DP175). These new co-dominant markers will be a starting point for researchers making use of the markers for genetic mapping and diversity analysis of date palm.

Current knowledge in lentil genomics and its application for crop improvement.

Most of the lentil growing countries face a certain set of abiotic and biotic stresses causing substantial reduction in crop growth, yield, and production. Until-to date, lentil breeders have used conventional plant breeding techniques of selection-recombination-selection cycle to develop improved cultivars.These techniques have been successful in mainstreaming some of the easy-to-manage monogenic traits. However, in case of complex quantitative traits, these conventional techniques are less precise. As most of the economic traits are complex, quantitative, and often influenced by environments and genotype–environment interaction, the genetic improvement of these traits becomes difficult. Genomics assisted breeding is relatively powerful and fast approach to develop high yielding varieties more suitable to adverse environmental conditions. New tools such as molecular markers and bioinformatics are expected to generate new knowledge and improve our understanding on the genetics of complex traits. In the past, the limited availability of genomic resources in lentil could not allow breeders to employ these tools in mainstream breeding program.The recent application of the next generation sequencing and genotyping by sequencing technologies has facilitated to speed up the lentil genome sequencing project and large discovery of genome-wide single nucleotide polymorphism (SNP) markers. Currently, several linkage maps have been developed in lentil through the use of expressed sequenced tag (EST) derived simple sequence repeat (SSR) and SNP markers.These maps have emerged as useful genomic resources to identify quantitative trait loci imparting tolerance to biotic and abiotic stresses in lentil. In this review, the current knowledge on available genomic resources and its application in lentil breeding program are discussed.

Molecular Approaches and Breeding Strategies for Drought Tolerance in Barley

Barley genotypes, in particular landraces and wild species, represent an important source of variation for adaptive traits that may contribute to increase yield and yield stability under drought conditions, and that could be introgressed into improved varieties. Traits that have been investigated include physiological/biochemical and developmental/ morphological traits. Yield performance under drought is particularly a complex phenomenon, and plants exhibit a diverse range of genetically complex mechanisms for drought resistance. Quantitative trait loci (QTL) studies with and without H. spontaneum have shown that developmental genes, notably those involved in flowering time and plant stature show pleiotropic effects on abiotic stress tolerance and ultimately determine yield. Problems associated with the hybridization of H. spontaneum such as alleles with deleterious effects on field performance could be best addressed in the advanced backcross (AB-) QTL analysis. It was interesting to see that in AB-QTL populations like in balanced populations major QTL overshadowed minor QTL-alleles. Nevertheless, crosses with H. spontaneum, AB-QTL populations and association studies with H. spontaneum have also identified new alleles and genes that are related to abiotic stress tolerance. In order to identify genes that are related to drought tolerance microarrays analysis to monitor gene expression profiles for plants exposed to limited water environment is performed. Several studies with rapid dehydration treatment have shown that osmotic-stress-inducible genes could explain the response to drought stress in plants. Another development is the identification and use of nucleotide polymorphisms (SNP) in genes related to abiotic stress tolerance. An understanding of the combined function and expression of genes involved in various abiotic stresses, could help identify candidate genes underlying QTL of interest.

Advances in Lentil Genomics

Lentil is a diploid (2n = 2X = 14) self-pollinating crop with a genome size of 4 Gbp. The use of genomics tools in lentil breeding programs has been limited, since available genomic resources are not adequate. Recent advances in high-throughput genotyping and sequencing technologies have brought in new impetus in the development of genetic and genomic resources and high resolution marker-trait association in lentil. Their integration in marker-assisted breeding is expected to improve the precision and efficiency in breeding programs with accelerated and directed genetic gains in crops like lentil. Molecular markers are expected to facilitate indirect selection for difficult traits, introgression of novel genes into adapted varieties, pyramiding genes from different sources, and combining multiple stress resistance. The present review highlights recent advances in lentil genomics and future outlook in the light of rapid advancement in the genomics tools.

Optimization of sequence alignment for simple sequence repeat regions

BackgroundMicrosatellites, or simple sequence repeats (SSRs), are tandemly repeated DNA sequences, including tandem copies of specific sequences no longer than six bases, that are distributed in the genome. SSR has been used as a molecular marker because it is easy to detect and is used in a range of applications, including genetic diversity, genome mapping, and marker assisted selection. It is also very mutable because of slipping in the DNA polymerase during DNA replication. This unique mutation increases the insertion/deletion (INDELs) mutation frequency to a high ratio - more than other types of molecular markers such as single nucleotide polymorphism (SNPs).SNPs are more frequent than INDELs. Therefore, all designed algorithms for sequence alignment fit the vast majority of the genomic sequence without considering microsatellite regions, as unique sequences that require special consideration. The old algorithm is limited in its application because there are many overlaps between different repeat units which result in false evolutionary relationships.FindingsTo overcome the limitation of the aligning algorithm when dealing with SSR loci, a new algorithm was developed using PERL script with a Tk graphical interface. This program is based on aligning sequences after determining the repeated units first, and the last SSR nucleotides positions. This results in a shifting process according to the inserted repeated unit type.When studying the phylogenic relations before and after applying the new algorithm, many differences in the trees were obtained by increasing the SSR length and complexity. However, less distance between different linage had been observed after applying the new algorithm.ConclusionsThe new algorithm produces better estimates for aligning SSR loci because it reflects more reliable evolutionary relations between different linages. It reduces overlapping during SSR alignment, which results in a more realistic phylogenic relationship.

Effects of Temperature Stresses on the Resistance of Chickpea Genotypes and Aggressiveness of Didymella rabiei Isolates

Chickpea (Cicer arietinum L.) is an important food and rotation crop in many parts of the world. Cold (freezing and chilling temperatures) and Ascochyta blight (Didymella rabiei) are the major constraints in chickpea production. The effects of temperature stresses on chickpea susceptibility and pathogen aggressiveness are not well documented in the Cicer-Didymella pathosystem. Two experiments were conducted under controlled conditions using chickpea genotypes and pathogen isolates in 2011 and 2012. In Experiment 1, four isolates of D. rabiei (AR-01, AR-02, AR-03 and AR-04), six chickpea genotypes (Ghab-1, Ghab-2, Ghab-3, Ghab-4, Ghab-5 and ICC-12004) and four temperature regimes (10, 15, 20, and 25°C) were studied using 10 day-old seedlings. In Experiment 2, three chickpea genotypes (Ghab-1, Ghab-2, and ICC-12004) were exposed to 5 and 10 days of chilling temperature exposure at 5°C and non-exposed seedlings were used as controls. Seedlings of the three chickpea genotypes were inoculated with the four pathogen isolates used in Experiment 1. Three disease parameters (incubation period, latent period and disease severity) were measured to evaluate treatment effects. In Experiment 1, highly significant interactions between genotypes and isolates; genotypes and temperature; and isolate and temperature were observed for incubation and latent periods. Genotype x isolate and temperature x isolate interactions also significantly affected disease severity. The resistant genotype ICC-12004 showed long incubation and latent periods and low disease severity at all temperatures. The highly aggressive isolate AR-04 caused symptoms, produced pycnidia in short duration as well as high disease severity across temperature regimes, which indicated it is adapted to a wide range of temperatures. Short incubation and latent periods and high disease severity were observed on genotypes exposed to chilling temperature. Our findings showed that the significant interactions of genotypes and isolates with temperature did not cause changes in the rank orders of the resistance of chickpea genotypes and aggressiveness of pathogen isolates. Moreover, chilling temperature predisposed chickpea genotypes to D. rabiei infection; developing multiple stress resistance is thus a pre-requisite for the expansion of winter-sown chickpea in West Asia and North Africa.

Identifying water-responsive and drought-tolerant chickpea genotypes

Abstract. This study quantifies the responses of drought-tolerant genotypes of chickpea (Cicer arietinum L.) to water availability under three irrigation regimes: rainfed (T1), 30% of full supplemental irrigation (T2), and full supplemental irrigation (T3). Sixteen genotypes of chickpea were tested in a split-plot arrangement in a randomised complete block design with three replications. Drought-resistance score (DRS), days to 50% flowering, plant height, days to maturity (DTM), grain yield (GY), biological yield (BY), 100-seed weight, average number of pods per plant (PoN), and average number of seeds per plant (SN) were measured. ANOVA indicated significant differences between treatments, years, and genotypes. Two genotypes, FLIP03-145C and ILC588, showed high drought tolerance accompanied by lower DTM, and they produced the highest GY (9.3 g plant–1). Strong and significant (P < 0.001) correlations were observed between GY and BY (0.94), SN (0.93), and PoN (0.94). The GY, BY, SN, and PoN traits were significantly (P < 0.001) correlated with DRS (–0.51 to –0.58). Ten genotypes performed better under T2 than T3, indicating a limitation in response to more water availability. Three genotypes (FLIP03-145C, ILC3182, and ILC588) are recommended for the national programs of Mediterranean countries as being drought-tolerant and especially responsive to water.