Melatonin mitigation of herbicide-induced injury to guar crop improves nodulation

Abstract

The guar plant, or cluster bean, forms a weak symbiosis with rhizobia, and it is sensitive to herbicides. We hypothesized that application of melatonin to guar seeds, leaves, or both protect against metabolic injury from eight herbicides, and strengthening the symbiosis. Imazethapyr and 2,4-DB did not injure guar and its rhizobium partner. Root nodulation was severely damaged with pendimethalin and less with bentazon. A reduction in guar's total dry weight, which ranged from 14% with bentazon to 28% with bromoxynil, was observed, indicating metabolic stress. When no herbicide was applied, seeds coated with melatonin had no effect. When herbicides were applied, it partially mitigated herbicide-induced injury. Foliar application of melatonin protected guar completely against bentazon, bromoxynil, and oxyfluorfen, protected nodulation.