Application of pesticides suppress foliar proanthocyanidin content in Leucaena species

Pesticides are routinely used to protect plants in agricultural and ecological studies that investigate plant secondary metabolism, although the impact of exposure to agrochemicals on the concentrations of secondary metabolites in plant tissues is largely unknown. To screen potential pesticides for use on Leucaena species, the phytotoxic effects of four foliar applied systemic insecticides and one miticide on growth and proanthocyanidin (PA) status of seedlings of six Leucaena species were evaluated in a glasshouse experiment. All pesticides were applied at recommended rates in deionized water, with a surfactant, until excess spray ran off the leaves. These were compared to a water-only control. Plant dry matter (DM) production and the PA concentration (butanol–HCl) in the youngest fully expanded leaves (YFEL) were recorded. All pesticide treatments reduced DM production (P<0.05) across Leucaena species by 13–28% compared to control plants. Application of methidathion, dicofol and dimethoate suppressed mean extractable PA concentrations across Leucaena species by 59, 40 and 23%, respectively (P<0.05), while pirimicarb and demeton-S-methyl did not affect plant extractable PA status (P>0.05). Bound PA contents were not affected by pesticide application. Results highlight the need to understand the impact that application of non-treatment agrochemicals has on the PA status of plants under investigation, in order to prevent phytotoxic interactions confounding the interpretation of experimental results.