title: Mode of action of acibenzolar-S-methyl against sheath blight of rice, caused by Rhizoctonia solani Kühn.
abstract: The mode of action of acibenzolar-S-methyl (BTH) was investigated against sheath blight of rice and its pathogen, Rhizoctonia solani. BTH exhibited limited fungitoxicity against R solani, in the form of reduced mycelial growth, hyphal browning and sclerotia formation. Parasite fitness of mycelia and sclerotia formed on BTH-amended media was also reduced. When applied as soil drench or foliar spray, BTH inhibited both disease development on inoculated sheaths and its spread to the younger sheaths. The degree of protection against sheath blight increased with increase in duration between BTH application and inoculation. The curative effect of BTH was poor. When applied through roots a protective effect of BTH was visible even with only a 1-h interval between application and inoculation. However, in the case of foliar application, protective effect was recorded only when the gap between application and inoculation was 24 h. BTH reduced the frequency of penetration by R solani, colonization of host tissue and spread of the hyphae from primary lesions to form secondary lesions. BTH induced swelling of hyphal tips on the sheath surface, formation of papillae, browning of penetrated epidermal cells and degeneration of intra-cellular hyphae colonizing epidermal and mesophyll cells. Therefore, the protective effect of BTH against sheath blight was due to combination of its host defence-inducing activity and its adverse effect on growth and vigor (parasite fitness) of the pathogen.
authors.affiliation: Department of Plant Pathology, College of Agriculture, GB Pant University of Agriculture & Technology, Pantnagar 263 145, India.
authors.forename: Rashmi
authors.initials: R
authors.lastname: Rohilla
authors.forename: U S
authors.initials: US
authors.lastname: Singh
authors.forename: R L
authors.initials: RL
authors.lastname: Singh
mesh_terms: D004305:Dose-Response Relationship, Drug; D005659:Fungicides, Industrial / Q000494:pharmacology*; D007113:Immunity, Innate / Q000187:drug effects; D012275:Oryza / Q000187:drug effects* / Q000382:microbiology; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000187:drug effects / Q000382:microbiology; D018517:Plant Roots / Q000187:drug effects / Q000382:microbiology; D012232:Rhizoctonia / Q000187:drug effects* / Q000472:pathogenicity; D013830:Thiadiazoles / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D005659:Fungicides, Industrial; D013830:Thiadiazoles; C099403:S-methyl benzo(1,2,3)thiadiazole-7-carbothioate