Tropospheric ozone as a fungal elicitor

Current ambient ozone levels mitigate the effect of Puccinia striiformis on wheat: Is Mediterranean wheat ready for pre-industrial background ozone levels?

Increasing surface ozone is a main concern for crop production in the Global Change framework, especially in the Mediterranean basin where climate conditions favor its photochemical formation. Meanwhile, increasing common crop diseases, such as yellow rust, one of the most important pathogens affecting global wheat production has been detected in the area in recent decades. However, the impact of O₃ on the occurrence and impact of fungal diseases is scarcely understood. A close-to-field-conditions assay (Open Top Chamber facility) situated in a Mediterranean cereal rainfed farming area was carried out to study the impact of increasing O₃ levels and N-fertilization on spontaneous fungal outbreaks in wheat. Four O₃-fumigation levels reproducing pre-industrial to future pollutant atmospheres with additional 20 and 40 nL L^-1 over the ambient levels were considered (7 h-mean ranging from 28 to 86 nL L^-1). Two top N-fertilization supplementations (100 and 200 kg ha^-1) were nested within the O₃ treatments; foliar damage, pigment content and gas exchange parameters were measured. Pre-industrial natural background O₃ levels strongly favored the yellow rust infection, where the O₃-polluted levels currently observed at the farm highly benefited the crop, mitigating the presence of rust by 22 %. However, future expected high O₃-levels neutralized the beneficial infection-controlling effect by inducing early wheat senescence, decreasing the chlorophyll index of the older leaves by up to 43 % under the higher O₃ exposure. Nitrogen promoted the rust infection by up to 49.5 % without interacting with the O₃-factor. Achieving future air quality standards might require considering new varietal improvement programs, to be able to adapt crops to an increased pathogen tolerance without requiring the assistance provided by O₃-pollution.

Effect of elevated ozone and carbon dioxide interaction on growth, yield, nutrient content and wilt disease severity in chickpea grown in Northern India

Wilt caused by Fusarium oxysporum, sp. Ciceris (FOC) is an important disease causing losses up to 10% in chickpea yield. Experiments were conducted growing chickpea in free air ozone and carbon dioxide enrichment rings under four treatments of elevated ozone (O3) (EO:60 ± 10 ppb), elevated carbon dioxide (CO2) (ECO2:550 ± 25 ppm), combination of elevated CO2 and O3 (EO + ECO2) and ambient control for quantifying the effect on growth, yield, biochemical and nutrient content of chickpea. For studying the impact on wilt disease, chickpea was grown additionally in pots with soil containing FOC in these rings. The incidence of Fusarium wilt reduced significantly (p < 0.01) under EO as compared to ambient and ECO2. The activities of pathogenesis-related proteins chitinase and β-1,3- glucanase, involved in plant defense mechanism were enhanced under EO. The aboveground biomass and pod weight declined by 18.7 and 15.8% respectively in uninnoculated soils under EO, whereas, in FOC inoculated soil (diseased plants), the decline under EO was much less at 8.6 and 9.9% as compared to the ambient. Under EO, the activity of super oxide dismutase increased significantly (p < 0.5, 40%) as compared to catalase (12.5%) and peroxidase (17.5%) without any significant increase under EO + ECO2. The proline accumulation was significantly (p < 0.01) higher in EO as compared to EO + ECO2, and ECO2. The seed yield declined under EO due to significant reduction (p < 0.01) in the number of unproductive pods and seed weight. No change in the protein, total soluble sugars, calcium and phosphorus content was observed in any of the treatments, however, a significant decrease in potassium (K) content was observed under EO + ECO2. Elevated CO2 (554ppm) countered the impacts of 21.1 and 14.4 ppm h (AOT 40) O3 exposure on the seed yield and nutrient content (except K) in the EO + CO2 treatment and reduced the severity of wilt disease in the two years' study.

Antioxidative and antifungal response of woody species to environmental conditions in the urban area

The complexity of ecological conditions in urban areas imposes the plant species need for the development of various biochemical and physiological adaptive strategies. The aim of our research was to examine the antioxidative and antifungal metabolism of species Pinus nigra, Picea omorika, Tilia cordata and Betula pendula from the area of Banja Luka City (urban area) during two vegetation seasons (spring and autumn) and compared with the same species from forest habitats. Changes in the protein concentration, activity and isoenzyme profiles of peroxidases (POD, EC 1.11.1.7), content and antioxidative activity of total phenols and antifungal activity in leaves and needles of the plants from the urban area and forest habitats were monitored. The obtained results indicate that urban areas induce changes in antioxidative metabolism in all examined species, but that the response is species specific. The most sensitive parameter that indicates different adaptation strategy of Pinus nigra, Picea omorika, Tilia cordata and Betula pendula to environment conditions in the urban area were peroxidase isoenzyme patterns. Less specific parameter was phenol content even though there are some indications for role of their antioxidative capacity in the adjustment to specific habitat. In addition, each species had different metabolic strategy to cope with the changes caused by the urban environment.

Early physiological responses of Pinus pinea L. seedlings infected by Heterobasidion sp.pl. in an ozone-enriched atmospheric environment

The presence of the American root-rot disease fungus Heterobasidion irregulare Garbel. & Otrosina was detected in Italian coastal pine forests (Pinus pinea L.) in addition to the common native species Heterobasidion annosum (Fries) Brefeld. High levels of tropospheric ozone (O3) as an atmospheric pollutant are usually experienced in Mediterranean pine forests. To explore the effect of interaction between the two Heterobasidion species and ozone pollution on P. pinea, an open-top chamber (OTC) experiment was carried out. Five-year-old P. pinea seedlings were inoculated with the fungal species considered (H. irregulare, H. annosum and mock-inoculation as control), and then exposed in charcoal-filtered open-top chambers (CF-OTC) and non-filtered ozone-enriched chambers (NF+) from July to the first week of August 2010 at the experimental facilities of Curno (North Italy). Fungal inoculation effects in an ozone-enriched environment were assessed as: (i) the length of the inoculation lesion; (ii) chlorophyll a fluorescence (ChlF) responses; and (iii) analysis of resin terpenes. Results showed no differences on lesion length between fungal and ozone treatments, whereas the short-term effects of the two stress factors on ChlF indicate an increased photosynthetic efficiency, thus suggesting the triggering of compensation/repair processes. The total amount of resin terpenes is enhanced by fungal infection of both species, but depressed by ozone to the levels observed in mock-inoculated plants. Variations in terpene profiles were also induced by stem base inoculations and ozone treatment. Ozone might negatively affect terpene defences making plants more susceptible to pathogens and insects.