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  • Author or Editor: M. Arabi x
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Barley ( Hordeum vulgare L.) is a major field crop grown worldwide. Field research was undertaken at ICARDA’s (International Center for Agriculture Research in Dry Area) main station in Northwest Syria to evaluate barley doubled haploid (DH) and mutants lines for agronomic traits (grain yield, plant height and days to heading) and resistance to scald ( Rhynchosporium secalis ) under natural infection conditions for two consecutive years. Significant differences were found among lines in the percentage of infected leaf area. However, they exhibited a continuous range of response from very susceptible to resistant. Seven lines had significantly lower percentage of infected leaf area with disease than did the other lines, which are associated with potential for grain yield and earliness. These lines could be considered as possible donors in further barley breeding programs.

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The competitive and adaptive capacity of Cochliobolus sativus were determined using the two major pathotypes in populations on barley in Syria Pt1 and Pt4, which differed widely in their virulence. Following greenhouse co-inoculation with the two pathotypes, Pt4 frequency average increased from the first to the last of four infection cycles, but decreased for Pt1. The number of lesions caused by Pt4 was individually higher than their mixture on both barley cultivars, Bowman and WI 2291. Moreover, the number of lesions was increased over the four cycles on both cultivars. The results suggest that isolates of different pathotypes would adapt at different rates in a mixed environment due to competitive advantage imposed by their virulence properties.

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The effects of Mycosphaerella graminicola , the causal agent of Septoria tritici blotch of wheat on the content and quality of storage proteins were studied. Field research was undertaken by comparing plots with and without artificial inoculation. Twenty-one Syrian cultivars, 11 ( Triticum aestivum L.) and 10 ( T. turgidum var. durum Desf.) were used in this study. The results show high differences in the susceptibility levels among cultivars which were subsequently divided into four groups: resistant, moderately resistant, moderately susceptible and highly susceptible. Results also showed that protein content decreased significantly in severely infected cultivars. However, the disease did not affect the protein quality using both A-PAGE and SDS-PAGE techniques.

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The heterogeneity among ten most widely grown old, recently released varieties and landraces of Syrian durum wheat was studied using amplified fragment length polymorphism (AFLP) markers. The 11 primer combinations used in this study amplified 533 scorable AFLP loci of which 141 (26.5%) were polymorphic. The values of average polymorphic information content (PIC) for these markers were estimated to be 0.34. The dissimilarity (D) values ranged from 0.120 to 0.729 with an average 0.421. The PCA analysis with the entire AFLP data separated the landraces from the durum wheat cultivars. The low PIC and dissimilarity values among modern varieties might be attributed to the rigorous selection pressure aimed at cultivar purity and associated breeding practices. It is included that AFLP markers can be used for detecting polymorphism leading to genotype identification and for estimating genetic diversity.

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Powdery mildew, caused by Blumeria graminis f. sp. hordei (Bgh) is a common foliar disease of barley worldwide. The creation of new cultivars with durable resistance to Bgh is highly desirable. This work was undertaken to examine the resistance to Bgh in 10 genetically diverse barley parents, and to evaluate their general combining ability (GCA) and specific combining ability (SCA) effects toward determining the genetic basis of disease resistance. Two experiments, in a growth chamber on seedling and in the field on adult plant stages, were conducted using a randomized complete block design with three replicates. The parents expressing differences in their reactions to Bgh were crossed in a half-diallel mating design to generate 45 full-sib families. Genetic component analysis showed significant effects for both GCA and SCA under both experiments suggesting that additive as well as non-additive genetic mechanisms were involved in the expression of resistance in these parents. The estimate of narrow-sense heritability was 0.63 and broad-sense heritability was 98% indicating that selection for the disease resistance should be effective in these crosses. Resistant parents ‘Banteng, PK 30-136 and ‘Igri’ had significantly negative GCA effects, suggesting their prime suitability for use in barley breeding programs to improve resistance to Bgh.

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Cochliobolus sativus, the causal agent of common root rot (CRR), is a devastating fungal pathogen of barley that can cause significant yield losses worldwide. The development of resistant cultivars has proven difficult, therefore, in this work, CRR-resistant barley germplasm was developed by crossing three resistant-by-susceptible cultivars currently used in Europe and West Asia. Following greenhouse evaluations of 150 doubled haploid lines derived from these crosses, 40 lines were evaluated under artificial infection conditions using incidence and severity parameters during two consecutive seasons. Data showed significant differences among barley lines with a continuum of resistance levels ranging from highly susceptible to resistant which were consistent in both seasons. However, five promising lines had slightly lower CRR disease than the others. Additionally, significant differences (P <0.05) in mean incidence and severity values were found among lines, with values being consistently higher in the susceptible ones. However, CRR severity increased linearly as incidence increased in both seasons. All together, the present study suggests that, the newly identified resistance lines can serve as potential donors for ongoing CRR resistance breeding program to generate high-yielding commercial barley cultivars, and that the positive correlation between CRR parameters I and S may be beneficial for many types of studies on this disease.

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Crop simulation models use allometric relationships to predict plant height from vegetative characteristics. The objective of this study was to find relationships between plant height (PH) and number of leaves on main stem (NLMS), stem dry weight (SDW) (g plant−1) and total vegetative components (leaves and stems) dry weight (TVDW) (g plant−1) in wheat (Triticum aestivum L.). For this purpose, an experiment was conducted using seven wheat cultivars including two durum wheat cultivars (Arya and Taro) and five bread wheat cultivars (Darya, Kuhdasht, Shiroudi, Tajan and Zagros) under irrigated and rainfed conditions during 2008-2009 at Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran. The experimental design was a randomized complete block design with four replications. Sampling was started from beginning of tillering and continued until maturity. A segmented nonlinear regression model was used to describe allometric relationships between PH and the vegetative characteristics. The results showed that there was no significant difference between cultivars and the two conditions for allometric relationships, so one equation was usable for all cultivars under both irrigated and rainfed conditions. Significant relationships were found between PH and NLMS (R2 = 0.94), SDW (R2 = 0.95) and TVDW (R2 = 0.95). These equations can be used for estimation of PH in simulation models of wheat.

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Antagonistic microorganisms have been used as biological control agents to reduce the use of chemical fungicides in the control of crop diseases. The present work was conducted to determine the antagonistic potential of Bacillus sp. isolates against the soil-borne fungus Cochliobolus sativus, the causal agent of barley common root (CRR) disease. Out of 525 isolates, 40 were showed in vitro antagonistic activity against the virulent C. sativus isolate CRR16. On the basis of 16S rRNA gene sequencing Bacillus sp. isolates are identified as B. atrophaeus, B. subtilis, Paenibacillus polymyxa, B. amyloliquefaciens, B. simplex and B. tequilensis. Results showed that Bacillus sp. had significant (P<0.05) antagonistic activities against the C. sativus where the percentage of radial growth inhibition of the fungi colonies ranged from 59 to 92%, compared to the untreated control. The B. subtilis isolate SY41B had the highest inhibition effect on the vegetative growth zones as compared with the other species isolates. In view of these, our results indicate that the antagonistic effect of the Bacillus sp. isolates may be important contributors as a biocontrol approach that could be employed as a part of integrated CRR management system.

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The biotrophic Blumeria graminis (Bg) and the necrotrophic Cochliobolus sativus; (Cs) are economically important fungal pathogens of barley globally. To better understand barley mechanisms to resist these pathogens, changes in salicylic acid (SA) and its responsive genes particularly the pathogenesis related PR1, PR2, PR3 and PR5 were evaluated using qRT-PCR across four time points post infection. Data showed that SA contents significantly increased (P = 0.001) in infected plants of both resistant and susceptible genotypes 24 h post inoculation in comparison with non-infected controls. In addition, time-course tests revealed a notable contradiction in the defense-related genes expression patterns between barley and Bg and Cs interactions, showing that expression patterns of the same defense-associated genes were altered in adaptation to different pathogens. PR1 and PR2 genes were highlyactivated inresistant plants infected with the necrotrophic pathogen Cs rather than of the biotrophic one. The uniformity in barley defense response mechanisms could be in convention with the well-accepted notion that these responses are high intense in the resistant genotype. Our work provides useful information on the expected role of SA pathways in barley towards biotrophic and necroptrophic pathogens with different lifestyles.

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Scald (Rhynchosporium secalis; Rs) and spot blotch (Cochliobolus sativus; Cs) are important diseases of barley (Hordeum vulgare L.) worldwide. Similar mechanisms and gene transcripts are assumed to be involved in the barley defense response since both these pathogens are necrotrophic fungi. In the current study, the transcriptome in leaves of the same barley genotype WI2291 inoculated with Rs and Cs was compared at different times postinoculation. Comparison of data for barley Rs- and Cs- inoculated plants with mockinoculated plants revealed gene expression changes that included basal defense transcripts and transcripts specific to the establishment of a necrotrophic interaction with associated fungi. During barley–pathogen interaction pathway, WI2291 activated a higher number of genes and pathways in response to Rs infection than in response to Cs invasion. However, families of genes encoding pectin-degrading enzymes, secondary metabolism enzymes, transporters and peptidases are expanded to cover Rs and Cs at an early stage following inoculation. Our results demonstrate differences in the pathways and activated genes of barely cv. WI291challenged by Rs and Cs, and that expression patterns of the same defenseassociated genes were altered in adaptation to different pathogens. Our work provides new insights into the underlying mechanisms related to regulation of different pathways in response to fungal infection.

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