Impact of Gall Midge, Orseolia Oryzae (Wood-Mason) Infestation on Total Phenols, Proline and Indole Acetic Acid in Paddy (Oryza Sativa Linn.) Genotypes

Abstract

The impact of gall midge infestation on total phenols, proline and indole acetic acid (IAA) contents in rice genotypes was investigated under laboratory conditions. The resistant rice genotypes showed an increased phenol and decreased proline and IAA contents in the growing apical meristem due to infestation. Significant and rapid accumulation of total phenols (0.24–0.59 mg/g) was observed at the third, seventh, and the ninth day after midge infestation in resistant genotypes compared to susceptible ones. The rapid accumulation of phenols in resistant genotypes following gall midge infestation highlights the inducible biochemical pathways involving synthesis of phenolic precursors and further oxidation into toxic quinones. Even in the susceptible genotypes, a slight increase (0.22–0.31 mg/g) was observed initially. It may be associated with gall initiation process because phenols act as IAA-oxidase inhibitors resulting in hyper-auxinity in gall tissue that leads to formation of nutritive tissue on which the gall midge feed. Significant and rapid accumulation of proline (2.96−13.50 µg/g) from the third, seventh and ninth day after infestation was recorded only in susceptible genotypes indicating their role under stress conditions. Likewise, the higher accumulation of IAA (3.16−8.18 µg/g) was observed in all the susceptible genotypes. Thus, rapid accumulation of IAA in relation to insect infestation in susceptible genotypes clearly indicated their role in gall formation because IAA acts as a growth regulator.