Histochemical characterization of early response to Cochliobolus sativus infection in selected barley genotypes

EVALUATION OF XYLANASE PRODUCTION FROM FILAMENTOUS FUNGI WITH DIFFERENT LIFESTYLES

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.

Natural Variation in Elicitation of Defense-Signaling Associates to Field Resistance Against the Spot Blotch Disease in Bread Wheat (Triticum aestivum L.)

Spot blotch, caused by the hemibiotropic fungus Bipolaris sorokiniana, is amongst the most damaging diseases of wheat. Still, natural variation in expression of biochemical traits that determine field resistance to spot blotch in wheat remain unaddressed. To understand how genotypic variations relate to metabolite profiles of the components of defense-signaling and the plant performance, as well as to discover novel sources of resistance against spot blotch, we have conducted field studies using 968 wheat genotypes at 5 geographical locations in South-Asia in 2 years. 46 genotypes were identified as resistant. Further, in independent confirmatory trials in subsequent 3 years, over 5 geographical locations, we re-characterized 55 genotypes for their resistance (above 46 along with Yangmai#6, a well characterized resistant genotype, and eight susceptible genotypes). We next determined time-dependent spot blotch-induced metabolite profiles of components of defense-signaling as well as levels of enzymatic components of defense pathway (such as salicylic acid (SA), phenolic acids, and redox components), and derived co-variation patterns with respect to resistance in these 55 genotypes. Spot blotch-induced SA accumulation was negatively correlated to disease progression. Amongst phenolic acids, syringic acid was most strongly inversely correlated to disease progression, indicating a defensive function, which was independently confirmed. Thus, exploring natural variation proved extremely useful in determining traits influencing phenotypic plasticity and adaptation to complex environments. Further, by overcoming environmental heterogeneity, our study identifies germplasm and biochemical traits that are deployable for spot blotch resistance in wheat along South-Asia.

The role of a cytosolic superoxide dismutase in barley-pathogen interactions

Reactive oxygen species (ROS), including superoxide ( O2·-/ HO2·) and hydrogen peroxide (H2 O2 ), are differentially produced during resistance responses to biotrophic pathogens and during susceptible responses to necrotrophic and hemi-biotrophic pathogens. Superoxide dismutase (SOD) is responsible for the catalysis of the dismutation of O2·-/ HO2· to H2 O2 , regulating the redox status of plant cells. Increased SOD activity has been correlated previously with resistance in barley to the hemi-biotrophic pathogen Pyrenophora teres f. teres (Ptt, the causal agent of the net form of net blotch disease), but the role of individual isoforms of SOD has not been studied. A cytosolic CuZnSOD, HvCSD1, was isolated from barley and characterized as being expressed in tissue from different developmental stages. HvCSD1 was up-regulated during the interaction with Ptt and to a greater extent during the resistance response. Net blotch disease symptoms and fungal growth were not as pronounced in transgenic HvCSD1 knockdown lines in a susceptible background (cv. Golden Promise), when compared with wild-type plants, suggesting that cytosolic O2·-/ HO2· contributes to the signalling required to induce a defence response to Ptt. There was no effect of HvCSD1 knockdown on infection by the hemi-biotrophic rice blast pathogen Magnaporthe oryzae or the biotrophic powdery mildew pathogen Blumeria graminis f. sp. hordei, but HvCSD1 also played a role in the regulation of lesion development by methyl viologen. Together, these results suggest that HvCSD1 could be important in the maintenance of the cytosolic redox status and in the differential regulation of responses to pathogens with different lifestyles.