Photosynthesis of Eucalyptus globulus with Mycosphaerella leaf disease

Abstract

Summary• Mycosphaerella leaf disease (MLD) is a major cause of foliage damage in Eucalyptus globulus plantations. Our study is the first to describe the physiological effects of MLD on E. globulus leaves. It involved measurements on both field and potted plants.• Changes in photosynthetic parameters in response to MLD were quantified in a study using gas exchange techniques.• There was a negative linear relationship between light-saturated photosynthesis ( A max ) and leaf-level damage from MLD. Reductions in A max were proportionally greater than might be expected from the reduction in green leaf area as a result of the disease, indicating that asymptomatic tissue also was affected by MLD. The reductions in A max were not related to increases in stomatal resistance, but were a result of reduced activity of ribulose bisphosphate carboxylase (Rubisco) and changes in the capacity for ribulose bisphosphate (RuBP) regeneration. Changes in mesophyll resistance to CO 2 were also implicated.• The effect of MLD was similar at different sites and irrespective of tree-level infection, suggesting a general leaf-level response of E. globulus to MLD. Key words:Eucalyptus globulus , light-saturated photosynthesis ( A max ), maximum rate of Rubisco activity ( V cmax ), Mycosphaerella leaf disease (MLD), potential electron transport rate ( J max ), ribulose bisphosphate carboxylase (Rubisco), ribulose bisphosphate (RuBP), stomatal conductance.

Few Mendelian Genes Underlie the Quantitative Response of a Forest Tree, Eucalyptus globulus, to a Natural Fungal Epidemic

“…cryptica at Woolnorth, identified by Milgate et al (2005a), and both M. cryptica and M. nubilosa at Ridgley (Carnegie and Ades 2002) and possibly also at Weilangta (Pinkard and Mohammed 2006) ,1 year after planting. Both species of Mycosphaerella are capable of causing severe damage in isolation (Milgate et al 2005a,b), although they often cooccur in diseased trees.…”

“…Crown damage from MLD can range from ,10% necrosis of leaves to extreme cases of complete defoliation and tree death. However, even relatively minor damage can cause a significant loss in growth (Carnegie and Ades 2002) because the disease adversely affects photosynthesis beyond a simple reduction in photosynthetic area (Pinkard and Mohammed 2006).…”

Mycosphaerella and Teratosphaeria diseases of Eucalyptus; easily confused and with serious consequences

“…Eucalyptus spp. are generally more susceptible to infection by Mycosphaerella and Teratosphaeria species during their juvenile leaf phase and the leaf infections caused by these fungi reduce the photosynthetic capacity, leading to premature defoliation and stunting of growth (Park and Keane 1982b;Lundquist and Purnell 1987;Carnegie and Ades 2003;Milgate et al 2005b;Pinkard and Mohammed 2006).…”

Photosynthetic gas exchange and antioxidative system in common bean plants infected by Colletotrichum lindemuthianum and supplied with silicon

“…The decrease in the net carbon assimilation rate of infected leaves has been attributed to decreases in mesophyll and/ or stomatal conductance of CO 2 , impairments in the rates of biochemical reactions of photosynthesis, changes in the number or structure of chloroplasts or changes in the secretion of phytotoxic chemicals into asymptomatic tissue (Berghaus & Reisener, 1985;Meyer et al, 2001;Pinkard & Mohammed, 2006). In the bean-C. lindemuthianum pathosystem, changes in the net carbon assimilation rate are exhibited during the necrotrophic phase: the inhibition of the net carbon assimilation rate takes place in the green tissue around the infection site and has been associated with stomatal closure and reduced ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity (Meyer et al, 2001).…”