Gas Exchange and Emission of Chlorophyll Fluorescence during the Monocycle of Rust, Angular Leaf Spot and Anthracnose on Bean Leaves as a Function of their Trophic Characteristics

Abstract

Measurements related to gas exchange and chlorophyll fluorescence emission were taken from healthy and diseased bean leaves with rust, angular leaf spot, and anthracnose during lesion development for each disease. The experiments were performed at different temperatures of plant incubation, and using two bean cultivars. The main effect of temperature of plant incubation was in disease development. There was no significant difference between cultivars in relation to disease development and in magnitude of physiological alterations when disease severity was the same for each cultivar. These diseases reduced the net photosynthetic rate and increased the dark respiration of infected leaves after the appearance of visible symptoms and the differences between healthy and diseased leaves increased with disease development. The transpiration rate and stomatal conductance were stable during the monocycle of rust, however, these two variables decreased in leaves with angular leaf spot and anthracnose beginning with symptom appearance and continuing until lesion development was complete. Carboxylation resistance was probably the main factor related to reduction of photosynthetic rate of the apparently healthy area of leaves with rust and angular leaf spot. Reduction of the intercellular concentration of CO2, due to higher stomatal resistance, was probably the main factor for leaves with anthracnose. Chlorophyll fluorescence assessments suggested that there was no change in electron transport capacity and generation of ATP and NADPH in apparently healthy areas of diseased leaves, but decreases in chlorophyll fluorescence emission occurred on visibly lesioned areas for all diseases. Minimal fluorescence was remarkably reduced in leaves with angular leaf spot. Maximal fluorescence and optimal quantum yield of photosystem II of leaves were reduced for all three diseases. Bean rust, caused by a biotrophic pathogen, induced less damage to the regulation mechanisms of the physiological processes of the remaining green area of diseased leaves than did bean angular leaf spot or anthracnose, caused by hemibiotrophic pathogens. The magnitude of photosynthesis reduction can be related to the host–pathogen trophic relationships.

Relationships between leaf pigments and photosynthesis in common bean plants infected by anthracnose

“…It provides a cooling effect to leaves (leaf thermoregulation), but also transports compounds from the roots to the leaves (Kerbauy 2008). Our results are similar to those reported by Bassanezi et al (2002) where two Phaseolus vulgaris cultivars presented lower transpiration rates after Colletotrichum lindemuthianum infection. Cavalcanti et al (2006) studied the consequences of Xanthomonas vesicatoria infection in Lycopersicon esculentum plants, also finding decreased transpiration.…”

Impact of Erysiphe alphitoides on transpiration and photosynthesis in Quercus robur leaves

“…A direct effect of the leaf pathogen on photosynthetic processes could be a reduction of carboxylation efficiency due to a possible impact on RUBISCO or on other enzymes of the Calvin cycle (Pennypacker et al 1990;Niederleitner and Knoppik 1997;Mayr et al 2001). Leaf pathogens can also alter light interception and photochemistry due to chlorophyll decay and consequently limitation in light-driven electron fluxes (Holloway et al 1992;Niederleitner and Knoppik 1997;Bassanezi et al 2002).…”

“…However, to properly assess the impact of oak powdery mildew on whole-tree physiology, we need to know the relationship between severity of leaf infection and physiological dysfunction such as reduction of A n or altered transpiration, which has not yet been studied. Fraction of leaf area infected is usually not an efficient estimate of the magnitude of pathogen impact on leaf CO 2 assimilation (Shtienberg 1992;Bassanezi et al 2002;Robert et al 2004). Bastiaan (1991) introduced the concept of virtual lesions to assess the impact of a pathogen on leaf physiology.…”

Wheat leaf photosynthesis loss due to leaf rust, with respect to lesion development and leaf nitrogen status

“…For bean rust ( Uromyces appendiculatus ) Bassanezi et al . (2001Bassanezi et al . ( , 2002 included necrotic tissue as well in the disease assessment.…”