Photosynthetic changes in wheat cultivars with contrasting levels of resistance to blast

Abstract

Wheat blast, caused by Pyricularia oryzae, is currently the main disease that threat to food security and wheat production in the world. This study investigated the photosynthetic responses of wheat plants from cultivars BR‐18 (moderately resistant) and BRS‐Guamirim (susceptible), differing in their levels of resistance to blast, by using leaf gas exchange and rapid light curves analysis focusing primarily on the asymptomatic (AS) and symptomatic (S) phases of disease development. The photosynthetic capacity of plants from cultivar BRS‐Guamirim was compromised by diffusional CO2 limitations and inefficient photoprotection mechanism at the AS phase of blast due to reductions in CO2 assimilation, stomatal conductance, transpiration rate and fluorescent quantum efficiency (Fv/Fm). For cultivar BR‐18, the loss in photosynthesis was minimized due to an efficient control in the regulated energy dissipation [Y(NPQ)] avoiding losses by latent heat [Y(NO)]. Additionally, Fv/Fm was a promissory physiological indicator of blast during its AS phase while Y(NPQ) and Y(NO) were more sensitive at the S phase of the disease. In conclusion, the physiological parameters Fv/Fm, Y(NQP) and Y(NO) can be used as physiological markers in wheat breeding programs seeking in the development of cultivars resistant to blast.

Physiological and Biochemical Aspects of Silicon-Mediated Resistance in Maize against Maydis Leaf Blight

“…In addition to the parameters related to Chl a fluorescence, the quantification of the pool of photosynthetic pigments is a stronger indicator of the decreased efficiency of the photosynthetic apparatus of plants infected by hemibiotrophic and necrotrophic pathogens due to the action of hydrolytic enzymes and selective non-host toxins that directly affect chloroplasts and their protein complexes [ 28 , 34 ]. The loss of functionality of the photosynthetic pigments is one of the main effects caused by B. maydis infection in maize leaves [ 8 ].…”

Chlorophyll a Fluorescence: A Method of Biotic Stress Detection

“…During the plant-pathogen interactions, plants infected by pathogens have reported reductions in CO 2 assimilation, stomatal dynamic alterations (stomatal closure), chronic inhibition of the photosystems, higher dissipation of energy by chlorophyll a fluorescence (non-photochemical mechanisms), alterations in the concentration of photosynthetic pigments, chloroplasts structural damage, losses in leaf area index, changes in the source-sink ratio, and changes in the profiles of genes, proteins, and metabolic related to photosynthesis [1,8,9,52]. The pathogen infection in the foliar tissue causes loss in the sunlight conduction capacity due to the cellular damage affecting the photosynthetic activity and consequent development of chlorotic and necrotic zones product of the action of hydrolytic enzymes, non-host selective toxins, and reactive oxygen species (ROS) [1,53].…”

“…CO 2 assimilation by the photosynthetic process is a permanent source of primary metabolism, and their products are the main energetic nutrient for pathogens colonizing plant tissues, as well as molecules related to metabolic pathways from secondary metabolism [1,54]. Studies performed in the last 20 years have allowed understanding how pathogens reprogram the metabolic flux of the carbohydrate's metabolism in detriment of the plant growth and yield demands [1,8,42,54]. From the metabolic perspective, several pathogens rapidly metabolize sucrose through invertase enzymes which hydrolyze sucrose to fructose and glucose increasing the hexoses pool [8,14,55].…”

“…Studies performed in the last 20 years have allowed understanding how pathogens reprogram the metabolic flux of the carbohydrate's metabolism in detriment of the plant growth and yield demands [1,8,42,54]. From the metabolic perspective, several pathogens rapidly metabolize sucrose through invertase enzymes which hydrolyze sucrose to fructose and glucose increasing the hexoses pool [8,14,55]. Metabolites such as fructose, glucose, and hexoses are energetic substrates for other metabolic pathways more complex that under biotic stress those molecules become a nutrient source for pathogens; however, alterations in the sugar concentrations induce the expression of defense genes and cell death considering that sugars act as signaling molecules to regulate the expression of some genes [56].…”

“…To study the photosynthesis, several methodologies have been developed involving determinations based on changes in CO 2 and water vapor differential concentrations using infrared sensors (infrared gas analyzer (IRGA)) through which it is possible calculate the leaf gas exchange parameters such as net CO 2 assimilation rate (A), stomatal closed (g s ), CO 2 intercellular concentration (C i ), and transpiration rate (E) [7]. Other methodologies developed in the biochemistry field are commonly applied in photosynthesis studies such as the quantification of the carbohydrates or enzymatic activities of the biochemical components associated with this pathway [8,9]. Under plant stress, the photosynthetic activity is a main physiological pathway evaluated, as the functionality of the photosynthetic machinery is affected by stress factors [10].…”