Rice defense responses to Bipolaris oryzae mediated by a strobilurin fungicide

Abstract

Strobilurins, also known as quinone outside inhibitors (QoIs), are one of the most important fungicide groups for controlling plant diseases. In addition, they can prime plants for enhanced defense against pathogen attack. Here, detailed biochemical and microscopic analyses were performed to investigate whether azoxystrobin (Az) could enhance defense responses to Bipolaris oryzae, the cause of brown spot of rice. Fungal infection increased the activity of all defense enzymes regardless of fungicide treatment. Az-sprayed plants displayed higher activities of β-1,3-glucanase, peroxidase, polyphenol oxidase (PPO) and lipoxygenase (LOX) in the absence of B. oryzae inoculation and of phenylalanine ammonia-lyase, PPO and LOX at 24 h after inoculation (hai) with B. oryzae compared to the control plants. Concentrations of total soluble phenols at 144 hai were higher in the Az-sprayed plants relative to their non-treated counterparts. Concentrations of lignin-thioglycolic acid derivatives were increased following fungal infection in the control plants. Hyphae from B. oryzae colonized bulliform, bundle sheath, epidermal, guard, mesophyll and vascular bundle cells besides intercellular spaces, but fewer and smaller fungal cells were noticed in the Azsprayed than in the control plants. Therefore, although Az transiently reprogrammed activities of some defense enzymes, its fungicidal activity appears to have played a major role in reducing B. oryzae infection.

Performance of a selected Trichoderma strain as plant pathogen inhibitor and biofertilizer

“…Their DNA sequences were uploaded to the GenBank database with accession 1; Figure 1). Bipolaris oryzae has been reported as a causal agent of brown spot disease in rice plants (Debona et al, 2018), which further supports this finding. As far as we are aware, this would be the first record of B. oryzae in Brunei Darussalam.…”

Evaluation of Pyraclostrobin as an Ingredient for Soybean Seed Treatment by Analyzing its Accumulation–Dissipation Kinetics, Plant-Growth Activation, and Protection Against Phytophthora sojae

“…46 Therefore, PAL activity can be used as a physiological index of plant immunity. 47 Our results showed that pyraclostrobin increased the PAL activity, which enhanced the plant defense against soybean diseases. A similar effect occurred in rice plants, in which azoxystrobin (a strobilurin fungicide) significantly enhanced the PAL activity.…”

“…PAL is also the key synthesis enzyme for lignin, which can increase the thickness of the cell wall, the degree of woody tissue, and form a mechanical barrier against pathogen invasion . Therefore, PAL activity can be used as a physiological index of plant immunity . Our results showed that pyraclostrobin increased the PAL activity, which enhanced the plant defense against soybean diseases.…”

Efficacy of Azoxystrobin on Mycotoxins and Related Fungi in Italian Paddy Rice

“…species but not in A. versicolor which was unchanged (Table 1). The effect of strobilurins against fungi is well documented, they appear able to enhance rice plant defenses against pathogen attacks [19,24], shown also in wheat against mycotoxigenic Fusarium species like F. graminearum [20]. The incidence of A. versicolor was too low to obtain a significant reduction in treatment with azoxystrobin, although a reduction of 5% was observed.…”

“…There are few fungicides allowed by Italian Regulations for rice; of these, azoxystrobin is an active ingredient belonging to the strobilurin chemical group and it is one of the most used on Italian rice because of its demonstrated efficacy on several crops and its major role in reducing Pyricularia grisea [18] and Bipolaris oryzae infections in rice [19] and Fusarium Head Blight (FHB) in wheat [20]. However, its possible effect on mycotoxins is still uncertain since in some studies the use of azoxystrobin in wheat could result in an increase in DON content up to 42% [21,22]; for this reason, this possible effect needs to be evaluated also in rice in order to assist farmers in their selection of fungicides.…”