Abstract
Pink stem borer (PSB) causes considerable yield losses to maize. Plant–insect interactions have significant implications for sustainable pest management. The present study demonstrated that PSB feeding, mechanical wounding, a combination of mechanical wounding and PSB regurgitation and exogenous application of methyl jasmonate have induced phenolic compound mediated defense responses both at short term (within 2 days of treatment) and long term (in 15 days of treatment) in leaf and stalk tissues of maize. The quantification of two major defense related phenolic compounds namely p-Coumaric acid (p-CA) and ferulic acid (FA) was carried out through ultra-fast liquid chromatography (UFLC) at 2 and 15 days after imposing the above treatments. The p-CA content induced in leaf tissues of maize genotypes were intrinsically higher when challenged by PSB attack at V3 and V6 stages in short- and long-term responses. Higher p-CA content was observed in stalk tissues upon wounding and regurgitation in short- and long-term responses at V3 and V6 stages. Significant accumulation of FA content was also observed in leaf tissues in response to PSB feeding at V3 stage in long-term response while at V6 stage it was observed both in short- and long-term responses. In stalk tissues, methyl jasmonate induced higher FA content in short-term response at V3 stage. However, at V6 stage PSB feeding induced FA accumulation in the short-term while, wounding and regurgitation treatment-induced defense responses in the long-term. In general, the resistant (DMRE 63, CM 500) and moderately resistant genotypes (WNZ ExoticPool) accumulated significantly higher contents of p-CA and FA content than susceptible ones (CM 202, BML 6) in most of the cases. The study indicates that phenolic mediated defense responses in maize are induced by PSB attack followed by wounding and regurgitation compared to the other induced treatments. Furthermore, the study confirmed that induced defense responses vary with plant genotype, stage of crop growth, plant tissue and short and long-term responses. The results of the study suggested that the Phenolic acids i.e. p-CA and FA may contribute to maize resistance mechanisms in the maize-PSB interaction system.
Highlights
The pink stem borer (PSB), Sesamia inferens Walker is one of the major insect pests in the winter maize which results 25.7–78.9 percent yield losses[1].The larvae feed inside the leaf sheath in groups and subsequently bore into the central shoot resulting in the formation of dead hearts
The present study tested the following hypotheses (i) Pink stem borer (PSB) feeding, mechanical wounding, a combination of mechanical wounding and PSB regurgitation, and exogenous application of methyl jasmonate (MeJA) would induce plants for defense responses; (ii) induced defense responses vary with stages of crop growth, plant tissue, and time; (iii) the maize genotypes respond differently to the induced treatments based on the degree of resistance to PSB
The findings in the present study provided important evidence that insect interaction-PSB feeding, and noninsect interactions including a combination of wounding and regurgitation, mechanical wounding, and exposure to methyl Jasmonate may induce defense responses in maize
Summary
The pink stem borer (PSB), Sesamia inferens Walker is one of the major insect pests in the winter maize which results 25.7–78.9 percent yield losses[1].The larvae feed inside the leaf sheath in groups and subsequently bore into the central shoot resulting in the formation of dead hearts. Results in a change in the biochemical constituents of plants[2,3] Plants recognize such external stimuli as herbivore attack and induces defense responses against h erbivores[4]. The direct defense responses include the change in morphological traits, production of secondary metabolites that either kills or slows the development of h erbivores[6,7], while indirect defenses include the release of volatile organic compounds that attract natural enemies of insect-pest(s). The present study tested the following hypotheses (i) PSB feeding, mechanical wounding, a combination of mechanical wounding and PSB regurgitation, and exogenous application of methyl jasmonate (MeJA) would induce plants for defense responses; (ii) induced defense responses vary with stages of crop growth, plant tissue, and time (short and long-term); (iii) the maize genotypes respond differently to the induced treatments based on the degree of resistance to PSB
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