Induction of Wheat Resistance to STB by the Endophytic Fungus serendipita Indica and pseudomonas Protegens.

BACKGROUND: Septoria tritici blotch (STB) caused by fungus Zymoseptoria tritici, is one of the important wheat (Triticum aestivum L.) diseases difficult to control because of the lack of wheat resistant cultivars. The use of biological control agents is one possible way for triggering host plant resistance to biotic and abiotic stresses. OBJECTIVE: In this study, we examined the ability of Serendipita indica and Pseudomonas protegens CHA0-mCherry in inducing the local wheat cultivar Tajan resistance to STB. MATERIALS AND METHODS: The interaction between biological control agents and the roots of wheat was evaluated. The experiment was conducted in a completely randomized design by three replicates. Spore suspension was supplied at concentrations of 107 and 109 for S. indica and bacteria isolate (CHA0-mCherry) respectively. Five treatments were applied including S. indica, CHA0-mCherry, S. indica and CHA0-mCherry co-inoculation, positive and negative control. Twenty-one days after inoculation, the interaction between biological agents and plant roots were evaluated through morphological traits and qPCR. The plant resistance, disease severity, and the correlation between resistance and disease severity were assessed. Pycnidial variation and agronomic traits were also evaluated. RESULTS: Twenty-one days after inoculation, both biological agents clearly colonized all treated roots of all treatments except in control plants as demonstrated by qPCR analysis. Chlamydospores were observed in the S. indica-treated hosts with the CHA0-mCherry colonizing assessment showing 5×109 CFU g-1 in the root. The asexual phase of the fungal pathogen, pycnidial diameter, was reduced in S. indica treated plants more considerably than in the other treatments. There was a positive correlation between resistance and disease severity mean when calculated by Pearson's correlation. There was a significant difference between the root length, fresh, and dry weight of root. Spore density was inversely correlated to resistance and disease severity, when compared with control, with CHA0-mCherry being the most effective in reducing the spore density. S. indica was the most effective in promoting root growth and stem biomass, when compared with control. CONCLUSIONS: Serendipita indica and Pseudomonas protegens CHA0-mCherry colonies showed a potential biological control activity and efficiently enhanced the plant resistance to Z. tritici in the treated wheat roots. The microbial biological control agents are very practical in crop protection against plant disease and can be very useful in sustainable agriculture. ABBREVIATIONS: PLSN: percentage of leave surface necrosis, DPI: day past inoculation, PLACL: percentage of leaf area covered by lesions, PPMLA: pycnidia per millimeter in leaf area.

Genetic diversity of Acidovorax oryzae in a single site in Mazandaran province, Iran.

Brown stripe, incited by Acidovorax oryzae is one of the most important and widespread diseases in rice (Oryza sativa) nurseries in Iran. Rice seedlings showing brown stripes were collected from suburb areas in southern Sari. Bacteria were isolated on plates of sorbitol neutral red agar. Species-specific PCR using trpB1/trpB2 and SEQID1/SEQID2 primer pairs resulted in amplification of the expected 478 bp and 514 bp long fragments, respectively. The 32 isolates subjected to REP-PCR analysis displayed 15 different banding profiles, with just one being shared by 10 isolates and 10 profiles were solitary and not shared by any isolates. Nonetheless, the isolates could not be different phenotypically. They appeared to be biochemically and nutritionally rather homogeneous while the genetic diversity as depicted in REP-PCR analysis was remarkable among the strains isolated from the closely located and even neighboring rice seedbeds. The implication of the findings in breeding programs is briefly discussed.

Isolation, Molecular Identification, and Mycotoxin Production of Aspergillus Species Isolated from the Rhizosphere of Sugarcane in the South of Iran.

Knowledge of the genetic diversity detected among fungal species belonging to the genus Aspergillus is of key importance for explaining their important ecological role in the environment and agriculture. The current study aimed to identify Aspergillus species occurring in the rhizosphere of sugarcane in the South of Iran, and to investigate their mycotoxin profiles. One-hundred and twenty-five Aspergillus strains were isolated from the soil of eight major sugarcane-producing sites, and were molecularly identified using sequences of partial -tubulin (benA) and partial calmodulin (CaM) genes. Our molecular and phylogenetic results showed that around 70% of strains belonged to the Aspergillus section Nigri, and around 25% of species belonged to the Aspergillus section Terrei. Species belonging to both sections are able to produce different mycotoxins. The production of mycotoxins was measured for each species, according to their known mycotoxin profile: patulin (PAT) and sterigmatocystin (STG) for Aspergillusterreus; ochratoxin A (OTA) and fumonisins for Aspergilluswelwitschiae; and OTA alone for Aspergillustubingensis. The data showed that the production of OTA was detected in only 4 out of 10 strains of A.welwitschiae, while none of the A.tubingensis strains analyzed produced the mycotoxin. Fumonisins were produced by 8 out of 10 strains of A.welwitschiae. Finally, none of the 23 strains of A.terreus produced STG, while 13 of them produced PAT. The occurrence of such mycotoxigenic plant pathogens among the fungal community occurring in soil of sugarcane fields may represent a significant source of inoculum for the possible colonization of sugarcane plants, since the early stages of plant growth, due to the mycotoxin production capability, could have worrisome implications in terms of both the safety and loss of products at harvest.

Bacteria-triggered systemic immunity in barley is associated with WRKY and ETHYLENE RESPONSIVE FACTORs but not with salicylic acid.

Leaf-to-leaf systemic immune signaling known as systemic acquired resistance is poorly understood in monocotyledonous plants. Here, we characterize systemic immunity in barley (Hordeum vulgare) triggered after primary leaf infection with either Pseudomonas syringae pathovar japonica (Psj) or Xanthomonas translucens pathovar cerealis (Xtc). Both pathogens induced resistance in systemic, uninfected leaves against a subsequent challenge infection with Xtc. In contrast to systemic acquired resistance in Arabidopsis (Arabidopsis thaliana), systemic immunity in barley was not associated with NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 or the local or systemic accumulation of salicylic acid. Instead, we documented a moderate local but not systemic induction of abscisic acid after infection of leaves with Psj. In contrast to salicylic acid or its functional analog benzothiadiazole, local applications of the jasmonic acid methyl ester or abscisic acid triggered systemic immunity to Xtc. RNA sequencing analysis of local and systemic transcript accumulation revealed unique gene expression changes in response to both Psj and Xtc and a clear separation of local from systemic responses. The systemic response appeared relatively modest, and quantitative reverse transcription-polymerase chain reaction associated systemic immunity with the local and systemic induction of two WRKY and two ETHYLENE RESPONSIVE FACTOR (ERF)-like transcription factors. Systemic immunity against Xtc was further associated with transcriptional changes after a secondary/systemic Xtc challenge infection; these changes were dependent on the primary treatment. Taken together, bacteria-induced systemic immunity in barley may be mediated in part by WRKY and ERF-like transcription factors, possibly facilitating transcriptional reprogramming to potentiate immunity.

Over-expression of the cell death regulator BAX inhibitor-1 in barley confers reduced or enhanced susceptibility to distinct fungal pathogens.

BAX inhibitor-1 (BI-1) is a conserved cell death regulator protein that inhibits mammalian BAX-induced cell death in yeast, animals and plants. Additionally, HvBI-1 suppresses defense responses and resistance to the powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh) when over-expressed in single epidermal cells of barley. To test the potential of ectopic expression of BI-1 to influence fungal interactions with crop plants, we produced stable transgenic barley plants expressing a green fluorescing protein (GFP) fusion of HvBI-1 under control of the cauliflower mosaic virus 35S promoter. GFP-HvBI-1 plants were fertile and did not display obvious developmental alterations when compared to wild type parents. GFP-HvBI-1 plants were more resistant to single cell death induced by ballistic delivery of a mammalian proapototic BAX expression construct and more susceptible to biotrophic Bgh. Microscopic observation of the interaction phenotype revealed that enhanced susceptibility, i.e. a higher degree of successful establishment of haustoria in epidermal cells, was associated with a reduced frequency of hypersensitive cell death reactions. In contrast, young seedlings of GFP-HvBI-1 barley were more resistant to Fusarium graminearum than wild type or azygous controls. Hence the effect of GFP-HvBI-1 on the outcome of a particular plant-fungus interaction appeared dependent on the lifestyle of the pathogen.