Relative phytotoxicity of hydroquinone on rice (Oryza sativa L.) and associated aquatic weed green musk chara (Chara zeylanica Willd.)

Relative toxicity of hydroquinone on rice (Oryza sativa L. var. Kranti) and associated submerged aquatic weed green musk chara (Chara zeylanica Willd.) was investigated for exploring possible use of the phytotoxin as herbicide in management of the weed. The hydroquinone was lethal to rice at and above 5 mM. It was phytotoxic to green musk chara at as low as 0.01 mM and lethal at 0.075-0.10 mM. The toxicity symptoms on the weed were dull green appearance followed by loss of biomass, and bleaching and fragmentation of the plant resulting in death in 3-12 days. The treated plants showed an excessive leakage of cellular constituents reflecting loss of cellular membrane integrity. There was a loss of metabolites like starch, sugars, amino acids, phenolics, protein, phosphorus, potassium, and chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid pigments with the advancement of the treatment and concomitant accumulation of oxidative stress as reflected by initial spurt of activity of some of the enzymes of the oxidative stress. Relatively higher toxicity of hydroquinone, a phytotoxin, to green musk chara than to rice appeared to be due to capability of the latter to withstand excessive accumulation of the chemical in the roots and inability of the chemical to reach the shoots. The phytotoxin appears to have killed the weed by causing massive damage to cellular membrane integrity, loss of metabolic activities and macromolecules, accompanied by associated starvation and accumulation of oxidative stress. Such a differential toxicity of a phytotoxin, which is short lived in the environment, to a crop and associated weed may have potential of weed management under certain circumstances.