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Effects of elevated O3- and CO2-concentrations on the resistance pattern of two unequal susceptible potato and barley cultivars with regard to fungal parasites (Dipl.-Ing.agr. M. Pleßl)
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Introduction:
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According to MANNING and TIEDEMANN (1995) rising carbon dioxide and ozone concentrations in the atmosphere have multifaceted effects on the resistance pattern of plants. Within the framework of SFB 607 "Growth and Parasite Defence" our project was dealing with the question, whether an elevation of CO2 (from 400 up to 700 ppm) and/or ozone (from ambient up to two-fold ambient) is resulting in a shift of resistance of potato infected with Phytophthora infestans and of barley infected with Drechslera teres. After 4 resp. 8 weeks of growth and simultaneous CO2- and ozone-treatment the progression of infection was viewed for 5 days (potato) resp. for 7 days (barley) in every variant. A putative change in susceptibility was aimed to be correlated with biochemical parameters.
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Literature: Manning W.J., Tiedemann A.v. (1995); Environmental Pollution 88: 219 - 245
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Results:
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A) potato (Solanum tuberosum)
A decrease in overground biomass was mainly detectable for the "two-fold ambient" ozone variants. Ozone impaired the production of tuber mass for the cultivar "Indira", too. While an elevated CO2-concentration of 700 ppm caused a slight decrease in overground biomass, it simultaneously led to a reinforced production of tuber mass, especially in the cultivar "Bettina" (Fig. 2).
A supply of 700 ppm CO2 caused an explicit decline in susceptibility in the cultivar "Indira" (dashed lines: 700 ppm CO2), especially in the variant with ambient ozone (Fig. 3).
The content of carbon (C) indicated a slight decrease in the elevated CO2-variants. The content of nitrogen (N) was reduced almost to a third in these variants (Fig. 4). Mainly due to the diminished N-content C/N-ratios were higher for elevated CO2 in both cultivars.
The two cultivars different susceptibility was confirmed by TaqMan-PCR (Fig. 5).
While the amount of fungal DNA stagnated in "Bettina", an increase of P. infestans-DNA could be noted during the 5 days after infection in the cultivar "Indira".
B) barley (Hordeum vulgare)
Elevated CO2 supported the production of roots mainly in the cultivar "Extract". At the same time above-ground biomass was also increased by 700 ppm CO2 in general. Ozone reduced above-ground biomass at times, the root-mass however was always decreased by "two-fold ambient" ozone compared with the ambient ozone treatment (Fig. 7).
"Two-fold ambient" ozone decreased the infected leaf area with D. teres in both cultivars (red and yellow line), whereas elevated CO2 rather increased the susceptibility (Fig. 8).
C/N-ratio: The results mainly resembled the potato experiment. The carbon content remained at the same level for all variants, the nitrogen content decreased slightly but explicit due to elevated CO2. Thus the C/N-ratio was increased for 700 ppm CO2.
The basic activity of the Pathogenesis Related - proteins chitinase and glucanase rose by "two-fold ambient" ozone for both cultivars at the date of harvesting (Tab. 1).
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Conclusions:
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A) The potato experiment
An increased CO2-concentration leads to enhanced tolerance in the potato - P. infestans interaction. This effect correlates with an increased C/N-ratio due to falling N-contents. This observation is inconsistent with the hypothesis that elevated CO2 is increasing susceptibility. C/N-ratio in leaves could still be responsible for determining susceptibility and for the efficiency of plant defence.
B) The barley experiment
In the case of barley - D. teres interactions raising ozone concentration decreases susceptibility. Higher basic levels of chitinase and glucanase activity might contribute to reduced susceptibility after a treatment with elevated ozone. Treatment with ozone increases the resistance of a host due to a stimulation of the secondary metabolism. In contrast to the potato experiment slightly increased C/N-ratios because of elevated CO2 promote the infection with D. teres.
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Additional analysis in the potato and barley experiment measured by other SFB groups:
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- Phenolics in potato plants (A 8 Treutter)
- Content of lignin, cellulose in both experiments, phenolics in barley plants (A1 Sandermann)
- N- and S-metabolites, carbohydrates in both experiments (X 1 Rennenberg)
- Content of cations (Ca2+, Mg2+, K+,Fe2+,Mn2+) (B 10 Göttlein)
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