Association between chronic root herbivory and changes in plant biomass, phytohormone levels, and nutrient content in rice

Abstract Root herbivory by insects can significantly impact plant performance and yield, particularly in crop production. Our understanding of the impact of chronic root herbivory by the rice water weevil, Lissorhoptrus oryzophilus , remains limited. Using an insecticidal seed treatment to manipulate levels of herbivory in small plots under natural field conditions, this study investigated the differences in rice water weevil infestation, plant growth, nutrient uptake, and phytohormone production in two rice cultivars. Two separate trials were established at different planting dates. For each trial, field plots were laid out following a randomized block design with six blocks and each block contained a factorial arrangement of cultivar (a hybrid and an inbred) and insecticidal seed treatment (seed-treated and nontreated). Rice water weevil densities were measured through root-soil core sampling at various time points after permanent flood establishment. Additionally, plant samples were collected at several timepoints for analyses of plant biomass, nutrient concentration, and phytohormones. Results showed that weevil densities varied over time with peak densities occurring around four weeks after permanent flood. The hybrid cultivar supported higher weevil densities but exhibited greater root and shoot biomass compared to the inbred cultivar. Weevil infestations negatively affected shoot biomass and nutrient concentrations, with significant reductions in several macronutrients and micronutrients over time. In addition, OPDA levels, a precursor of JA biosynthesis, were higher in the shoots of weevil-infested rice plants. Yield losses due to weevil infestations ranged from 8 to 35% with inbred cultivar experiencing greater yield losses than hybrid cultivar. Overall, our findings indicate that chronic root herbivory in rice was associated with reduced plant growth, yields, and nutrient uptake.