|RAHMAN, ALAMGIR - Pennsylvania State University|
|UDDIN, WAKAR - Pennsylvania State University|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2015
Publication Date: 6/1/2015
Citation: Rahman, A., Wallis, C.M., Uddin, W. 2015. Silicon induced systemic defense responses in perennial ryegrass against Magnaporthe oryzae infection. Phytopathology. 105:748-757.
Interpretive Summary: Fungicide-compatible management strategies are needed to control fungal diseases of perennial ryegrass. One possibility is the use of silicon as a soil amendment, which has been shown to induce plant resistance to different pathogens ultimately resulting in reductions in disease. To this end, development of gray leaf spot, caused by the fungal pathogen Magnaporthe oryzae, was compared between inoculated perennial ryegrass grown in non-amended soil and soil amended with three different levels of silicon. Grass grown in soil amended with silicon at a rate of 5 metric tons per hectare (6.48 mg per cm3) had reduced incidence and severity of gray leaf spot compared to controls. Further studies observed possible increased priming of host defenses that resulted in greater defense-associated enzyme and phenolic compound production following infection, which likely decreased pathogen colonization and reduced disease development. These findings suggest that the use of silicon as a soil amendment is a viable, cost-effective way to reduce gray leaf spot disease in perennial ryegrass.
Technical Abstract: Sustainable integrated disease management for gray leaf spot of perennial ryegrass may involve use of plant defense elicitors with compatible traditional fungicides to reduce disease incidence and severity. Silicon (Si) is a potential inducer or modulator of plant defenses against different pathogens. To this end, perennial ryegrass was inoculated with the causal agent of gray leaf spot, Magnaporthe oryzae, when grown in soil that was non-amended or amended with three different levels of silicon (1, 5, or 10 metric ton/ha). When applied at a rate of 1 and 5 metric ton/ha to soil, silicon was found to significantly suppress gray leaf spot in perennial ryegrass including a significant reduction of disease incidence (39.5%) and disease severity (47.3%) when at 5 metric ton/ha. Additional studies observed non-penetrated papillae or cell-wall appositions harboring callose, phenolic autofluorogens, and lignin-associated polyphenolic compounds in grass grown in silicon-amended soil. Regarding defense-associated enzyme levels, only following M. oryzae infection did grass grown in Si-amended soil exhibit greater activities of peroxidase (PRX) and polyphenol oxidase (PPO) than equivalent inoculated control plants. Also following infection with M. oryzae but not before, grass levels of several phenolic acids, including chlorogenic acid and flavonoids, and transcripts encoding the related enzymes phenylalanine ammonia lyase (PALa and PALb) and lipoxygenase (LOXa) were greater in plants grown in Si-amended soil than those grown in non-amended soil. These results suggest that because of Si-mediated increases in ryegrass host defense responses to M. oryzae, the use of silicon as a soil amendment has potential to become part of effective integrated disease management strategy to combat gray leaf spot disease.