The role of photoprotection in defence of two wheat genotypes against Zymoseptoria tritici

This study provides new insights into the role of photoprotection in preformed and induced defence of two wheat genotypes with contrasting phenotypes to infection by Zymoseptoria tritici. We investigated the mechanisms of the photoprotective response during early infection, including nonphotochemical quenching (NPQ), β-carotene-derived xanthophylls, reactive oxygen species, and the phytohormones abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA). Furthermore, we quantified the effects of pathogenesis on photosynthesis, stomatal control, and expression of plant defence molecular markers. The photoprotective mechanism of successful defence involved the qI component of NPQ leading to rapid down-regulation of photosystem II quantum yield and chlorophyll a:b, increased biosynthesis of the xanthophyll neoxanthin and ABA, and the expression of chloroplast-specific enzymes to engage in scavenging of O2●−. Elevated ABA in the resistant genotype correlated with preformed leaf defence traits including low stomatal density, increased expression of wax biosynthesis, and lignification. Z. tritici exhibited reduced germination and branching on the resistant host genotype and hijacked stomatal control in both genotypes by enhancing stomatal sensitivity to light. Increased biosynthesis of JA and anthocyanins, in contrast to SA, were quantified in the incompatible interaction. Our results indicate that ABA and JA in antagonistic action to SA were associated with defence in the resistant genotype, Cougar, against Z. tritici

Altered gene expression by sedaxane increases PSII efficiency, photosynthesis and growth and improves tolerance to drought in wheat seedlings

Succinate dehydrogenase inhibitor (SDHI) fungicides have been shown to increase PSII efficiency and photosynthesis under drought stress in the absence of disease to enhance the biomass and yield of winter wheat. However, the molecular mechanism of improved photosynthetic efficiency observed in SDHI-treated wheat has not been previously elucidated. Here we used a combination of chlorophyll fluorescence, gas exchange and gene expression analysis, to aid our understanding of the basis of the physiological responses of wheat seedlings under drought conditions to sedaxane, a novel SDHI seed treatment. We show that sedaxane increased the efficiency of PSII photochemistry, reduced non-photochemical quenching and improved the photosynthesis and biomass in wheat correlating with systemic changes in the expression of genes involved in defense, chlorophyll synthesis and cell wall modification. We applied a coexpression network-based approach using differentially expressed genes of leaves, roots and pregerminated seeds from our wheat array datasets to identify the most important hub genes, with top ranked correlation (higher gene association value and z-score) involved in cell wall expansion and strengthening, wax and pigment biosynthesis and defense. The results indicate that sedaxane confers tolerant responses of wheat plants grown under drought conditions by redirecting metabolites from defense/stress responses towards growth and adaptive development

Foliar application of isopyrazam and epoxiconazole improves photosystem II efficiency, biomass and yield in winter wheat

A range of fungicides including epoxiconazole, azoxystrobin and isopyrazam, were applied to winter wheat at GS 31/32 to determine their effect on photosystem II (PSII) efficiency, biomass and yield. Frequent, repeated measurements of chlorophyll fluorescence were carried on plants grown under different water regimes in controlled environment and in the field to establish the transiency of fluorescence changes in relation to fungicide application. Application of the succinate dehydrogenase inhibitor isopyrazam in a mixture with the triazole epoxiconazole increased PSII efficiency associated with a 28% increase in biomass in the controlled environment and 4% increase in grain yield in the field in the absence of disease pressure. Application of isopyrazam and epoxiconazole increased efficiency of PSII photochemistry (Fv'/Fm') as early as 4h following application associated with improved photosynthetic gas exchange and increased rates of electron transport. We reveal a strong, positive relationship between Fv'/Fm' and CO2 assimilation rate, stomatal conductance and transpiration rate in controlled environment and Fv'/Fm' detected just after anthesis on the flag leaf at GS 73 and grain yield in field. We conclude that application of a specific combination of fungicides with positive effects of plant physiology in the absence of disease pressure results in enhanced biomass and yield in winter wheat. Additionally, an accurate and frequent assessment of photosynthetic efficiency of winter wheat plants can be used to predict yield and biomass in the field. © 2014 Elsevier Inc

Chlorophyll fluorescence parameters allow the rapid detection and differentiation of plant responses in three different wheat pathosystems

The present study was undertaken to identify chlorophyll fluorescence (CF) parameters that can quantify changes in PSII associated with plant responses in three different wheat pathosystems of foliar, stem-base and ear diseases. The pathosystems included powdery mildew caused by Blumeria graminis, eyespot caused by Oculimacula yallundae or Oculimacula acuformis and Fusarium head blight (FHB) caused by Fusarium culmorum, F. avenaceum or F. langsethiae. Fast CF transients (OJIP) were analysed with the JIP-Test to determine changes in PSII photochemistry. Measurements on asymptomatic leaves showed that electron transport related parameters (ETo/RC, ψo and φEo) were important to identify varietal differences in resistance to powdery mildew during early stages of infection. The same parameters also allowed differentiation between F. langsethiae and other Fusarium spp. Where infections were caused by the necrotrophic pathogens, Oculimacula spp., F. culmorum or F. avenaceum, changes related to maximum efficiency of PSII photochemistry (Fv/Fm) as well as flux of dissipated (DIo/RC), trapped (TRo/RC), or absorbed (ABS/RC) energy per active reaction centers were significant in detecting biotic stress and the effectiveness of fungicide treatment for disease control. Our results demonstrated that Fv/Fm correlated significantly with visual disease and pathogen DNA of different wheat pathosystems. OJIP was shown as a sensitive technique that can be explored as diagnostic tool in future crop disease management and varietal breeding programs

Chlorophyll fluorescence parameters allow the rapid detection and differentiation of plant responses in three different wheat pathosystems

The present study was undertaken to identify chlorophyll fluorescence (CF) parameters that can quantify changes in PSII associated with plant responses in three different wheat pathosystems of foliar, stem-base and ear diseases. The pathosystems included powdery mildew caused by Blumeria graminis, eyespot caused by Oculimacula yallundae or Oculimacula acuformis and Fusarium head blight (FHB) caused by Fusarium culmorum, F. avenaceum or F. langsethiae. Fast CF transients (OJIP) were analysed with the JIP-Test to determine changes in PSII photochemistry. Measurements on asymptomatic leaves showed that electron transport related parameters (ETo/RC, ψo and φEo) were important to identify varietal differences in resistance to powdery mildew during early stages of infection. The same parameters also allowed differentiation between F. langsethiae and other Fusarium spp. Where infections were caused by the necrotrophic pathogens, Oculimacula spp., F. culmorum or F. avenaceum, changes related to maximum efficiency of PSII photochemistry (Fv/Fm) as well as flux of dissipated (DIo/RC), trapped (TRo/RC), or absorbed (ABS/RC) energy per active reaction centers were significant in detecting biotic stress and the effectiveness of fungicide treatment for disease control. Our results demonstrated that Fv/Fm correlated significantly with visual disease and pathogen DNA of different wheat pathosystems. OJIP was shown as a sensitive technique that can be explored as diagnostic tool in future crop disease management and varietal breeding programs