Combined whole-season effects of elevated ozone and carbon dioxide concentrations on a simulated wheat leaf rust (Puccinia recondita f. sp. tritici) epidemic.
J. Plant Dis. Prot.105, 555-566 (1998)
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A complete growth season with the physical climate and ozone pollution from 1 April to 31 July as recorded at a field site in Northern Germany, averaged over several years, was simulated in climate chambers and combined either with a current (370-400 mu l l(-1)) or enriched (620-650 mu l l(-1)) CO2 atmosphere. Wheat, grown from seedling emergence to maturity under the different physico-chemical climates, was inoculated with leaf rust (Puccinia recondita f. sp. tritici) at tillering stage and a rust epidemic was induced by repeated re-inoculations with the newly Formed inoculum. Ozone significantly reduced disease severity, uredospore production and increased the latent period of leaf rust on young planes, consequently inhibiting the epidemic spread on upper leaves of mature plants. Inhibiting effects of ozone on leaf rust development were not reflected by the early infection stages such as spore germination, germ tube growth, formation of infection hyphae, haustorial mother cells and haustoria, which remained largely unaffected by the ozone treatments. However, ozone induced a significantly higher extent of hypersensitive responses of the infected leaf tissue. Additionally, plants exposed to elevated ozone turned senescent much earlier than plants without this stress which prematurely degraded the growth conditions for the fungal pathogen. Enrichment with CO2 increased the rotal carbohydrate content in leaves but this had only minor effects on the disease. Thus, elevated CO2 only poorly compensated for the disease-inhibiting effects of ozone. The compensation of ozone effects on wheat leaf rust by elevated CO2 is much smaller than known compensatory effects of both gases on plans productivity.