Thais F Stella de Freitas1,2, Michael J Stout2, Josué Sant'Ana1. 1. Insect Ethology and Chemical Ecology Laboratory, Crop Protection Department, Federal University of Rio Grande do Sul, Porto Alegre, Brazil. 2. Department of Entomology, Louisiana State University, Baton Rouge, LA, USA.
Abstract
BACKGROUND: After herbivore attack, plants express inducible resistance-related traits activated by hormones, mainly jasmonic acid (JA) and salicylic acid (SA). Methyl jasmonate (MeJa) is a biologically active methyl ester of JA. Exogenous applications of JA, SA, and MeJa induce responses similar to herbivory by insects. In this study, rice, Oryza sativa L. (Poaceae), plants were treated with two concentrations of MeJa (2 and 5 mmol L-1 ), two concentrations of SA (8 and 16 mmol L-1 ) and herbivory to evaluate effects of elicitation and herbivory on resistance to the rice stink bug (RSB) Oebalus pugnax Fabricius, 1775 (Hemiptera: Pentatomidae), an injurious insect pest of rice in the United States. RESULTS: Nymphs developing on plants treated with SA 16 mmol L-1 took longer to reach adulthood than nymphs developing on check plants. Grains per panicle were higher in plants treated with SA 16 mmol L-1 and MeJa in both concentrations than in check treatment. Plants treated with SA emitted five of six volatile compounds identified in equal or higher amounts than plants subjected to previous herbivory, particularly methyl salicylate, a known defense-related compound. Salicylic acid 16 mmol L-1 was the treatment that elicited the highest amount of all volatiles. In the field assay, plots treated with SA 16 mmol L-1 showed lower spikelet sterility and a tendency for fewer bugs to be found in plots. CONCLUSION: Rice plants possess defense mechanisms that can be elicited using hormones as elicitors, mainly SA 16 mmol L-1 , to induce resistance against RSB.
BACKGROUND: After herbivore attack, plants express inducible resistance-related traits activated by hormones, mainly jasmonic acid (JA) and salicylic acid (SA). Methyl jasmonate (MeJa) is a biologically active methyl ester of JA. Exogenous applications of JA, SA, and MeJa induce responses similar to herbivory by insects. In this study, rice, Oryza sativa L. (Poaceae), plants were treated with two concentrations of MeJa (2 and 5 mmol L-1 ), two concentrations of SA (8 and 16 mmol L-1 ) and herbivory to evaluate effects of elicitation and herbivory on resistance to the ricestink bug (RSB) Oebalus pugnax Fabricius, 1775 (Hemiptera: Pentatomidae), an injurious insect pest of rice in the United States. RESULTS: Nymphs developing on plants treated with SA 16 mmol L-1 took longer to reach adulthood than nymphs developing on check plants. Grains per panicle were higher in plants treated with SA 16 mmol L-1 and MeJa in both concentrations than in check treatment. Plants treated with SA emitted five of six volatile compounds identified in equal or higher amounts than plants subjected to previous herbivory, particularly methyl salicylate, a known defense-related compound. Salicylic acid 16 mmol L-1 was the treatment that elicited the highest amount of all volatiles. In the field assay, plots treated with SA 16 mmol L-1 showed lower spikelet sterility and a tendency for fewer bugs to be found in plots. CONCLUSION:Rice plants possess defense mechanisms that can be elicited using hormones as elicitors, mainly SA 16 mmol L-1 , to induce resistance against RSB.