Silicon-Induced Systemic Defense Responses in Perennial Ryegrass Against Infection by Magnaporthe oryzae.
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) has previously been identified as a potential inducer or modulator of plant defenses against different fungal pathogens. To this end, perennial ryegrass was inoculated with the causal agent of gray leaf spot, Magnaporthe oryzae, when grown in soil that was nonamended or amended with three different levels of calcium silicate (1, 5, or 10 metric tons [t]/ha). When applied at a rate of 5 t/ha, calcium silicate 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%). Additional studies observed nonpenetrated papillae or cell-wall appositions harboring callose, phenolic autofluorogens, and lignin-associated polyphenolic compounds in grass grown in the Si-amended soil. Regarding defense-associated enzyme levels, only following infection did grass grown in Si-amended soil exhibit greater activities of peroxidase and polyphenol oxidase than equivalent inoculated control plants. Also following infection with M. oryzae, grass levels of several phenolic acids, including chlorogenic acid and flavonoids, and relative expression levels of genes encoding phenylalanine ammonia lyase (PALa and PALb) and lipoxygenase (LOXa) significantly increased in Si-amended plants compared with that of nonamended control plants. These results suggest that Si-mediated increase of host defense responses to fungal pathogens in perennial ryegrass has a great potential to be part of an effective integrated disease management strategy against gray leaf spot development.
First and third authors: Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park 16802; and second author: United States Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier, CA 93648.
Alamgir
A
Rahman
First and third authors: Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park 16802; and second author: United States Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier, CA 93648.
Christopher M
CM
Wallis
First and third authors: Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park 16802; and second author: United States Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier, CA 93648.
Wakar
W
Uddin
D017610:Calcium Compounds / Q000494:pharmacology*; D004156:Catechol Oxidase / Q000235:genetics; D005936:Glucans / Q000378:metabolism; D062385:Hydroxybenzoates / Q000378:metabolism; D008129:Lolium / Q000187:drug effects* / Q000235:genetics / Q000276:immunology; D020082:Magnaporthe / Q000502:physiology*; D010650:Phenylalanine Ammonia-Lyase / Q000235:genetics; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics / Q000276:immunology; D017640:Silicates / Q000494:pharmacology*
D017610:Calcium Compounds; D005936:Glucans; D062385:Hydroxybenzoates; D017640:Silicates; C048306:callose; D004156:Catechol Oxidase; D010650:Phenylalanine Ammonia-Lyase; C017616:phenolic acid; C031293:calcium silicate