Reactive Oxygen Species are not Increased in Resistant Oat Genotypes Challenged by Crown Rust Isolates

Abstract

Crown rust (Puccinia coronata Corda f.sp. avenae) can devastate oats (Avena sativa). Oxidative stress is part of the resistance mechanism in several pathosystems, but in the oat–crown rust system, it is unclear, especially regarding partial resistance. We evaluated the effects of P. coronata on oxidative stress in oat cultivars: URS 21 (partially resistant), Leggett (race‐specific resistant), URS22 and Clintland 64 (susceptibles). Seedlings and plants were inoculated with P. coronata uredospores. Cultivars were assessed for antioxidant enzyme activity and the reactive oxygen species (ROS) hydrogen peroxide and superoxide. Due to the importance of the partial resistance of URS21, this cultivar and URS 22 were also appraised for total phenolics and the relative expression of oxidative stress genes. Postinoculation, Leggett and URS 21 showed no increased peroxide levels. The susceptible cultivars increased ROS and ascorbate peroxidase activity. Clintland 64 increased also catalase activity, whereas URS 22 increased glutathione reductase and the expression of genes encoding antioxidant enzymes. URS 21 showed almost no antioxidant enzyme induction. Shortly after inoculation, URS 21 showed increased expression of genes encoding lipoxygenase and peroxidase. Cultivars URS 21 and Leggett accumulated cell wall fluorescent compounds, phenolics being detected in the former. Oxidative stress appears not to cause the hypersensitive response in this pathosystem, but late ROS accumulation did occur in the susceptible cultivars. Cultivar URS 21 may, differently from other known mechanism to date, reduce ROS accumulation by increasing the level of phenolics, resulting in later pathogen and cell death, showing non‐specific resistance to races of the pathogen also at seedling stage.

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“…It seems that in the partial resistance mechanism, observed in URS 21, the death of the fungus occurs first than the death of the cells, differing from the hypersensitive response, in which the cell is killed first (Graichen et al 2011). Another particularity observed in URS 21 is that the production of phenolic compounds was more pronounced than in a cultivar that presented hypersensitive response (Figueiró et al 2015).…”

Discriminating Important Agronomic and Industrial Parameters of White Oat Cultivars Treated with Fungicide Based on SIMCA Algorithm

“…In Southern Brazil, due to the highly complex and diverse pathogen populations, severe epidemics occur every year [11]. Crown rust is a major oat disease, occurring yearly in all oat-producing regions in Brazil [11], and yield losses caused by the disease can reach 50% [11,12].…”

“…Crown rust is a major oat disease, occurring yearly in all oat-producing regions in Brazil [11], and yield losses caused by the disease can reach 50% [11,12]. In addition, crown rust can reduce the grain quality, which negatively affects the industrialization and commercialization of oat grain [12].…”

RNAseq analysis reveals the role of secondary metabolism in the response of URS 21, a race‐nonspecific resistant cultivar, to crown rust

“…A similar mechanism has been described earlier for P. striiformis in wheat (Jiang & Kang, ). Cultivar URS 21 appears to limit reactive oxygen species (ROS) accumulation by inducing synthesis of phenolic compounds that might cause later pathogen and cell death, consequently limiting disease progression (Figueiró et al ., ).…”

“…This resistance, different from others, is expressed in both seedlings and adult plants. The genetic inheritance of URS 21 race‐nonspecific resistance (Zambonato et al ., ), the histopathological mechanisms (Graichen et al ., ) and the oxidative metabolism (Figueiró et al ., ) associated with it have been studied. The resistance seems to be defined by two major‐effect loci and three minor‐effect loci.…”