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.
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: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: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.
Authors:A. Al-Daoude, E. Al-Shehadah, A. Shoaib, M. Jawhar and M.I.E. Arabi
Spot blotch (SB) caused by the hemibiotrophic fungal pathogen Cochliobolus sativus is a destructive disease of barley worldwide. To better understand the mechanisms of resistance to this disease, the involvements of salicylic acid (SA), hydrogen peroxide (H2O2) and ion fluxes during the interaction between resistant and susceptible barley seedlings and C. sativus were investigated. Early SA accumulation in leaf tissues was accompanied with an increase in H2O2 concentration in both compatible and incompatible interactions. The resistant cultivar constitutively contained higher levels of H2O2 and SA, as well as during the 72 h as compared with the un-infected control (0 h). However, levels increased rapidly upon infection in both cultivars. Moreover, a markedly greater increase in ion fluxes from the compatible material compared with the incompatible one was observed. Results suggest that SA and H2O2 accumulation are important during both compatible and incompatible barley- C. sativus interactions.
Authors:A. Adam, M. I. E. Arabi, I. Edris and E. Al-Shehadah
The effect of four rhizobacterial strains on the severity of spot blotch disease
caused by cochliobolus sativus was evaluated for two growing
seasons under rainfed conditions. Three barley genotypes were used as host
plant. All strains reduced C. sativus severity, with effect
more pronounced when Pseudomonas putida BTP1 and
Bacillus subtilis Bs2508 were used. The disease reduction
was up to 56% in Arabi Abiad / P. putida BTP1. The grain yield
was not obviously affected by the presence of the rhizobacteria, except some
signifitive increase in season 2. Raising the resistance by soaking seed with
rhizobacterial strains might be of ultimate value in agriculture.
Authors:M. I. E. Arabi, H. Alek, E. Al-Shehadah and M. Jawhar
Long-term storage of Rhynchosporium secalis cultures is a challenge for any lab managing a working collection of isolates. In this work, the viability and pathogenicity of R. secalis stock cultures were tested after four years of storage at −20 °C in different concentrations of glycerol. Germinability were measured after each storage by collecting spores by coverslips and placing them on water agar in closed Petri dishes at 20–22 °C in the dark and allowed to germinate for 24 h. Additionally, at the end of each storage treatment, conidia were collected by coverslips from sporulated leaf lesions of symptomatic barley leaves and placed under similar conditions as non-stored controls.
Cultures of all stored isolates were viable with a spore germination rate of 72.28% (Rs22) after four years of storage at −20 °C in 60% glycerol. Low viability and contamination were observed when spores were stored in sterile distilled water and in Lima bean agar. All isolates continued to infect barley leaves after 4 years of storage. However, the pathogenicity was significantly (P <0.05) reduced in isolates stored in glycerol as compared with controls.
This work helps to preserve R. secalis for a long term period at −20 °C without any contamination; therefore, due to the low costs our results could be applicable for laboratories that have limited resources.
Authors:A. Shoaib, A. Aldaoude, M.I.E. Arabi, E. Al-Shehadah and M. Jawhar
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.
Authors:A. Aldaoude, A. Shoaib, E. Al-Shehadah, M. Rajeh, M. Jawhar and M.I.E. Arabi
Scald caused by Rhynchosporium secalis, is an economically important disease found worldwide. In order to profile genes and pathways responding to R. seclais infection, leaf transcriptomes before and after fungus inoculation in susceptible barley were compared using cDNA-AFLP technique. Transcriptional changes of 144 expressed sequence tags (ESTs) were observed, of which 18 have no previously described function. Functional annotation of the transcripts revealed a wide range of pathways including cell wall fortification, cytoskeleton construction and metabolic processes at different time points. Furthermore, the results of RT-PCR analysis on candidate genes, ABC transporters and lycine-specific demethylase were consistent with the cDNA-AFLP data in their expression patterns. Taken together, our data suggest that susceptible barley reprograms metabolic and biological processes to initiate a suitable response R. secalis infection.