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 (
) 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.
The competitive and adaptive capacity of
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.
The effects of
, 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 (
L.) and 10 (
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.
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
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.
Authors:M.I.E. Arabi, E. Al-shehadah and M. Jawhar
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.
Authors:M. I. E. Arabi, E. Al-Shehadah and M. Jawhar
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.
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.
Authors:A. Al-Daoude, H. Alek, M. Jawhar, E. Al-Shehadah, A. Shoiab and M. I. E. Arabi
The seed-borne (Pyrenophora graminea; Pg) and foliar
(Blumeria graminis; Bg) are two economically important
fungal pathogens of barley worldwide. Barley plant resistance genes, as the
pathogenesis related proteins play an important role in defense mechanisms. This
study aimed to monitor the expression of PR2 and
PAL pathogenesis related genes during
compatible/incompatible barley interaction with Pg and
Bg at different time points of disease development using
the Quantitative Real-time PCR technique (qRT-PCR).
Comparison of data showed that PR2 and PAL were
significantly over expressed in infected resistant and susceptible plants as
against their lower expression in controls,. Upregulation of these
defense-related genes during Pg and Bg
infections was companied with a slow development of disease symptoms at the time
course in the resistant genotype. qRT-PCR analysis revealed higher gene
expression in resistant barley plants inoculated with Pg as
compared with Bg, with a maximum expression for
PR2 (13.8 and 5.06-fold) and PAL (14.8 and
4.51-fold) respectively, at the latest stage of each disease development. It was
also noteworthy that PR2 and PAL genes, had
higher constitutive expression and faster induction for the both pathogens in
the resistant genotype as compared with the susceptible one.
Obtained results suggest that both genes, PR2 and
PAL, positively regulate Pg- and
Bg-resistance in barley plants during disease progress.
These expression patterns can provide useful insights to better understanding of
the barley–fungus interactions with different fungal lifestyles.
Authors:Y. Bakri, Y. Akeed, M. Jawhar and M.I.E Arabi
Xylanase plays an important role in the food, feed, and pulp/paper industry. Filamentous fungi have been considered as useful producers of this enzyme from an industrial point of view, due to the fact that they excrete xylanases into the medium. In this study, four fungal species belonging to different genera, i.e. Aspergillus, Cochliobolus, Pyrenophora, and Penicillium were isolated from different sources and compared for their ability to produce xylanase in submerged culture. The fungal species showed enzyme activity as determined by dinitrosalicylic acid (DNS) method. It was found that the two saprophytic Aspergillus strains, i.e A. terreus (Fss 129) and A. niger (SS7) had the highest xylanase activity of 474 and 294 U ml–1 at pH 7 and 8, respectively, in the presence of corn cob hulls after 120 h of incubation. The production of xylanase seemed to be strongly influenced by the interactive effect of initial pH on the fungi. Interestingly, xylanase was better produced by the saprophytic fungi of Aspergillus and Penicillium than by the plant pathogenic ones of Cochliobolus and Pyrenophora. This work provides additional information to support future research on fungi with different lifestyles for food industrial production of xylanase.
Authors:A. Al-Daoude, E. Al-Shehadah, A. Shoaib, M. Jawhar and M.I.E. Arabi
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.