Evidence for oxidative stress involved in physiological leaf spot formation in winter and spring barley

Detection of Ramularia collo-cygni from barley in Australia using triplex quantitative and droplet digital PCR

BACKGROUND

Ramularia leaf spot (RLS), caused by Ramularia collo-cygni, is an emerging threat to barley (Hordeum vulgare L.) production. RLS has been reported in Australia, however only minimal information is available regarding its detection and distribution. Due to initial asymptomatic growth in planta, slow growth in vitro and symptomatic similarities to net blotch and physiological leaf spots, detection of this pathogen can be challenging. Quantitative polymerase chain reaction (PCR)-based methods for R. collo-cygni-specific identification and detection have been described, however these assays have been demonstrated to lack specificity. False-positive detections may have serious implications, thus we aimed to design a robust R. collo-cygni-specific PCR method.

RESULTS

Using the phylogenetically informative RNA polymerase II second largest subunit (rpb2) and translation elongation factor 1-alpha (tef1-α) genes, along with the tef1-α gene of H. vulgare, a triplex assay was developed for both quantitative and droplet digital PCR. The triplex assay detected R. collo-cygni DNA in barley leaves from New South Wales, South Australia, Tasmania, Victoria and Western Australia. No R. collo-cygni DNA was detected in barley seed grown in Western Australia.

CONCLUSION

The presence of R. collo-cygni DNA has been confirmed in Australian barley crops, suggesting a distribution ranging across the southern barley growing regions of Australia. The R. collo-cygni-specific assay will be a valuable tool to assist with monitoring the distribution and impact of R. collo-cygni in Australia and other regions. © 2021 Society of Chemical Industry.

Mapping of agronomic traits, disease resistance and malting quality in a wide cross of two-row barley cultivars

Wide crosses between genetically diverged parents may reveal novel loci for crop improvement that are not apparent in crosses between elite cultivars. The landrace Chevallier was a noted malting barley first grown in 1820. To identify potentially novel alleles for agronomic traits, Chevallier was crossed with the modern malting cultivar NFC Tipple generating two genetically diverse recombinant inbred line populations. Genetic maps were produced using genotyping-by-sequencing and 384-SNP genotyping, and the populations were phenotyped for agronomic traits to allow the identification of quantitative trait loci (QTL). Within the semi-dwarf 1 (sdw1) region on chromosome 3H Chevallier conferred increased plant height and reduced tiller number, with QTL for these traits explaining 79.4% and 35.2% of the phenotypic variance observed, respectively. Chevallier was also associated with powdery mildew susceptibility, with a QTL on 1H accounting for up to 19.1% of the variance and resistance at this locus most likely resulting from an Mla variant from Tipple. Two novel QTL for physiological leaf spotting were identified on 3H and 7H, explaining up to 17.1% of the variance and with the Chevallier allele reducing symptom severity on 7H. Preliminary micromalting analysis was also undertaken to compare the malting characteristics of Chevallier and Tipple. Chevallier malt contained significantly lower levels of both α-amylase and wort β-glucan than Tipple malt, however no significant differences were observed for the remaining malting parameters measured. This suggests that the most obvious improvements in barley since the introduction of Chevallier are for agronomic traits such as height, yield and lodging resistance rather than for malting characteristics. Overall, our results demonstrate that this wide cross between Chevallier and Tipple may provide a source of novel QTL for barley breeding.

Application of ethylene diurea (EDU) in assessing the response of a tropical soybean cultivar to ambient O₃: nitrogen metabolism, antioxidants, reproductive development and yield

The present study deals with assessment of response of a tropical soybean cultivar to O3 in relation to photosynthetic pigments, chlorophyll fluorescence kinetics, antioxidative capacity, N assimilation enzymes, metabolites, growth and yield using ethylene diurea (EDU) given as a soil drench (400) ppm at an interval of 10 days after germination up to maturity. Mean O3 concentration was 42 ppb and accumulated threshold above 40 ppb (AOT 40) was 9.07 ppm h. Lipid peroxidation and total phenolics reduced, while increases in activities of antioxidative and nitrogen assimilation enzymes, ascorbic acid, protein, photosynthetic pigments, Fv/Fm ratio, number of leaves, flowers, pods, branches and yield attributes were found in EDU treated plants. EDU alleviated the negative effects of O3 by enhancing the first line of defense against ROS and protecting N assimilation enzymes at flowering and maintaining adequate supply of photosynthates to developing pods during pod filling stage. EDU provided maximum protection between flowering to pod filling stage.

The multigene family encoding germin-like proteins of barley. Regulation and function in Basal host resistance

Germin-like proteins (GLPs) have been shown to be encoded by multigene families in several plant species and a role of some subfamily members in defense against pathogen attack has been proposed based on gene regulation studies and transgenic approaches. We studied the function of six GLP subfamilies of barley (Hordeum vulgare) by selecting single mRNAs for gene expression studies as well as overexpression and gene-silencing experiments in barley and Arabidopsis (Arabidopsis thaliana). Expression of all six subfamilies was high in very young seedlings, including roots. The expression pattern gradually changed from developmental to conditional with increasing plant age, whereby pathogen attack and exogenous hydrogen peroxide application were found to be the strongest signals for induction of several GLP subfamilies. Transcripts of four of five GLP subfamilies that are expressed in shoots were predominantly accumulating in the leaf epidermis. Transient overexpression of HvGER4 or HvGER5 as well as transient silencing by RNA interference of HvGER3 or HvGER5 protected barley epidermal cells from attack by the appropriate powdery mildew fungus Blumeria graminis f. sp. hordei. Silencing of HvGER4 induced hypersusceptibility. Transient and stable expression of subfamily members revealed HvGER5 as a new extracellular superoxide dismutase, and protection by overexpression could be demonstrated to be dependent on superoxide dismutase activity of the encoded protein. Data suggest a complex interplay of HvGER proteins in fine regulation of basal resistance against B. graminis.

Residue level, persistence, and storage performance of citrus fruit treated with fludioxonil

The potential of postharvest dip treatments with fludioxonil (FLU) (a synthetic analogue of the bacterial metabolite of pyrrolnitrin), in controlling postharvest decay caused by Penicillium digitatum and Penicillium italicum of citrus fruit was investigated in comparison with the conventional fungicide imazalil (IMZ). The ultrastructural changes of fruit epicuticular wax was investigated as a function of water dip temperature, and the possible role of these changes was related to residue accumulation under FLU treatment. Residues retained by fruit were determined as a function of fungicide concentration, dip temperature, and fruit storage conditions. Scanning electron microscopy analysis revealed that fruit dipping in water at 30 or 40 degrees C did not cause differences in cuticular wax's ultrastructure in comparison to control fruit, while treatments at 50, 55, or 60 degrees C caused the disappearance of wax platelets, resulting in relatively homogeneous skin surface, due to partial "melting" of epicuticular wax. Residues of FLU in fruit treated at 20 or 50 degrees C were significantly correlated with the doses of fungicide applied. When equal amounts of fungicide were employed, the residue concentrations were notably higher (from 2.6- to 4-fold) in fruit treated at 50 degrees C than in fruit treated at 20 degrees C. The dissipation rate of FLU in "Salustiana" and "Tarocco" oranges was lower in fruit subjected to treatment at 50 degrees C. The minimal FLU concentration for almost complete decay control in artificially wounded fruit during 7-d storage at 20 degrees C was 400 mg/L active ingredient (ai) in fruit treated at 20 degrees C and 100 mg/L ai in fruit treated at 50 degrees C. Results on nonwounded Tarocco oranges subjected to 3 weeks of simulated quarantine conditions at 1 degrees C, plus 6 weeks of standard storage at 8 degrees C and an additional two weeks of simulated marketing period (SMP) at 20 degrees C revealed that almost complete decay control with FLU applications of 100 mg/L at 50 degrees C and 400 mg/L at 20 degrees C resulted in ca. 0.8 mg/kg FLU fruit residues, in agreement with results on wounded citrus fruit. When equal concentrations and temperatures were applied, FLU treatments were as effective as IMZ. In vitro trials showed a low sensitivity to FLU against P. digitatum and P. italicum isolates. MIC values for the complete inhibition of mycelium growth were >or=100 microg/mL, while ED(50) values ranged from 0.1 to 1 microg/mL for P. digitatum and from 1 to >100 microg/mL for P. italicum. The latter result suggests that care should be taken to avoid exclusive application of FLU in a sustainable program for management of fruit decay. However, integrating fungicide application and hot water dip may reduce the possibility of selecting fungicide-resistant populations of the pathogen, by increasing the effectiveness of the treatment.

Control of blue mold (Penicillium expansum) by fludioxonil in apples (cv Empire) under controlled atmosphere and cold storage conditions

A reduced risk fungicide, fludioxonil, was tested for its efficacy against blue mold caused by thiabendazole-resistant and -sensitive Penicillium expansum (Link) Thom in apples under three storage conditions. In a co-treatment, fludioxonil and inoculum were applied together to test the protective activity of the fungicide on wounds that had been aged for 1 or 2 days. The fungicide was also tested for its curative activity in post-inoculation treatment on apples that had been inoculated for 1 or 2 days. Fludioxonil was very effective as co-treatment and as post-inoculation treatment. At a concentration of 300 mg litre(-1), fludioxonil gave complete control of post-harvest blue mold caused by the thiabendazole-resistant and -sensitive P expansum for 105 days in controlled atmosphere (CA) storage at 2 (+/-1) degrees C, for 42 days in common cold storage at 4 (+/-1) degrees C and also in a shelf-life study for 6 days at 20 (+/-1) degrees C. Comparison on the effect of fludioxonil in CA storage and common cold storage showed that higher concentrations of fungicide were needed in cold storage than in CA storage. Fludioxonil at a concentration of 450 mg litre(-1), gave 98 and 92% control of blue mold of apples in the simulated shelf-life studies after CA and common cold storages, respectively. Fludioxonil has a potential to be incorporated in the fungicide resistance management strategies for control of blue mold in apples stored for 105 days.

Light-dependent oxidative stress determines physiological leaf spot formation in barley

ABSTRACT We reported previously that physiological leaf spot (PLS) formation in winter and spring barley is dependent on genotype-related oxidative stress under field conditions. In the present study, we searched for factors inducing PLS symptoms in the greenhouse similar to those observed in the field and investigated its relationship to reactive oxygen species (ROS) metabolism. We found that in the greenhouse, oxidative stress induced spring barley cv. Extract, which is sensitive to PLS, to express symptoms similar to those observed in the field. Leaves severely affected by PLS showed significantly lower activities of key enzymes in the Halliwell-Asada cycle such as ascorbate peroxidase, glutathione reductase, dehy-droascorbate reductase, and monodehydroascorbate reductase. The sensitive cultivar also showed lower levels of total superoxide dismutase (SOD) and Cu/Zn-SOD activity but a higher level of chloroplast-specific Fe-SOD activity than that of the insensitive cultivar. Thus, an unbalanced ROS metabolism in chloroplasts may trigger PLS incidence in sensitive cultivars, which is in agreement with the fact that light is essential for the induction of PLS expression under both field and greenhouse conditions. Accordingly, under greenhouse conditions, continuous light stress (7 days), but not light shock treatments, induced PLS similar to that of field conditions in sensitive cv. Extract, but not in resistant cv. Scarlett. Light with a high proportion of energy in the blue wavelength spectrum (350 to 560 nm) was significantly more PLS inductive than light with a pronounced red (photosynthetically active radiation) spectrum (580 to 650 nm). Exposure to ozone did not produce PLS-like symptoms. Furthermore, similar to earlier observations in the field, PLS symptom expression was closely correlated with the accumulation of superoxide (O(2) (-)) detected by both biochemical and histochemical assays. Taken together, these data suggest that PLS in barley is genotype-dependent but its expression appears to be induced by certain environmental stress factors, among which photosyn-thetically active radiation plays a major role.