Ozone Effects on Fungal Leaf Diseases of Wheat in Relation to Epidemiology

Abstract

Wheat plants at growth stages tillering, stem elongation, ear emergence and anthesis were exposed to 80, 160, 240 μg m−3 ozone for 5 days (7 h per day) and to charcoal‐filtered air. Post‐exposure inoculations with Septoria nodorum or Bipolaris sorokiniana revealed a faster growth of lesions on ozonated leaves. However, whereas maximum size of Septoria lesions was measured on leaves exposed to the highest concentration of O3, Bipolaris lesions developed best at 160 μg m−2 and were significantly reduced at 240 μg m−3 O3. These predisposing effects were largely independent of the four growth stages tested. The latent period of S. nodorum was inversely related to the lesion growth and particularly shortened by ozone at growth stages (GS) 37 and 55. The latent period of B. sorokiniana was most strongly shortened at GS 65 (anthesis). It is concluded that both diseases may be enhanced by ozone throughout the main growing season of wheat and that in particular S. nodorum epidemics may be accelerated by shortened latent periods at decisive stages of the early season. Zusammenfassung Ozonwirkung auf pilzliche Blattkrankheiten an Weizen in bezug zur Epidemiologie I. Nekrotrophe Pathogene Weizenpflanzen im Stadium Bestockung, Schossen, Ährenschieben und Blüte wurden mit 80, 160, 240 μg m−3 Ozon 5 Tage lang begast (7 Stunden täglich) bzw. aktivkohlegefilteiter Luft ausgesetzt. Nach anschließender Inokulation mit Septoria nodorum und Bipolaris sorokiniana, entstanden auf ozonbehandelten Blättern größere Läsionen. Während jedoch bei Septoria die größten Läsionen bei der höchsten Ozonkonzentration entstanden, war dies bei Bipolaris bei 160 μg m−3 der Fall, während sich bei 240 μg m−3 Ozon die Pilzläsionen deutlich schlechter entwickelten. Diese ozonbedingten Prädispositionseffekte konnten weitgehend in alien Entwicklungsstadien reproduziert werden. Die Latenzzeit von S. nodorum verhielt sich umgekehrt proportional zum Läsionenwachstum und war besonders stark bei EC 37 und EC 55 durch Ozon verkürzt. Bei B. sorokiniana war die Latenzzeit am stärksten bei EC 65 verkürzt. Es wird gefolgert, daß beide Krankheiten während der gesamten Hauptvegetationsperiode durch Ozon gefördert werden können, wobei der Epidemieaufbau insbesondere bei Septoria schon frühzeitig durch verkürzte Latenzzeiten beschleunigt werden kann.

Complex interplay of future climate levels of CO2, ozone and temperature on susceptibility to fungal diseases in barley

“…It is therefore tempting to suggest that ozone exposure prior to infection primed a defence response in the plant, leading to increased basal resistance against B. graminis . However, exposure to ozone concentrations above 100 ppb in wheat reduced powdery mildew disease as observed in this study, whereas concentrations similar to the ones applied here increased disease (von Tiedemann, ). The effect of ozone, therefore, seems to depend on the specific plant–pathogen interaction and the level of ozone exposure, even within closely related biotrophic pathogens.…”

“…This suggests that basal resistance against the biotrophic B. graminis and hemibiotrophic B. sorokiniana must be different despite the apparent similarities in the early infection process. Exposure to [O 3 ] comparable to the concentrations used here also increased infection with B. sorokiniana in wheat (von Tiedemann, ). However, higher concentrations (above 120 ppb) either had no or a negative effect on infection in B. sorokiniana and D. teres (von Tiedemann, ; Plessl et al ., ).…”

Effect of ozone and antioxidants on wheat and its pathogen — Bipolaris sorokininana

“…In the present study enhancement in susceptibility of O 3 predisposed wheat to B. sorokiniana, a hemibiotrophic pathogen was observed. This observation confirms the Tiedemann (1992) reports that susceptibility of wheat to Septoria nodorum and B. sorokiniana after O 3 exposure increased. Mikkelsen et al (2015) also reported increased and decreased infection by the hemibiotrophic spot blotch fungus and biotrophic powdery mildew fungus, respectively, under elevated O 3 , compared to ambient conditions, implying that O 3-induced changes in disease severity could be linked to the trophic lifestyle of the pathogens.…”

Wheat archive links long-term fungal pathogen population dynamics to air pollution

“…SO 2 has declined more rapidly than the other pollutants (35) and is much better correlated with the Broadbalk pathogen DNA data. It may act alone (36) or in a mixture with other pollutants (37) such as ozone, which is considered to favor infection by necrotrophic pathogens such as P. nodorum (23), presumably by inducing premature senescence of wheat tissues and nutrient leakage. By contrast, the hemibiotrophic M. graminicola, which penetrates leaves through stomata rather than directly through the cuticle and has a longer latent period than P. nodorum (6), might be adversely affected by SO 2 pollution, like other hemibiotrophs (38,39).…”