Herbicidal action of root -applied glufosinate -ammonium
Glufosinate-ammonium (GLA) is a post-emergence herbicide that inhibits glutamine synthetase (GS), synthesis of glutamine from glutamate. This inhibition results in NH4+ accumulation and ultimate plant death. GLA is usually effective as foliar spray at concentrations over 200 mg/L. Research on root applied GLA is lacking. The current research studied the effects of root-application of GLA on tomato plant growth, foliar NH 4+ accumulation, and ethylene evolution.
In a dose-response experiment under hydroponics, phytotoxicity symptoms appeared on tomato seedling with 25 or 50 mg GLA X at 6 days after treatment (DAT). Under soil conditions, GLA higher than 7.5 mg/pot caused toxicity symptoms in 2 days. With 3 and 5 mg/pot symptoms appeared at 4 DAT. 1.5 mg GLA/pot at 5 DAT. With an increase of GLA rate, shoot NH4+ concentration increased in hydroponics or soil experiments. In a time course experiment, at 4 DAT, GLA at 25 mg/L caused foliar toxicity symptoms and overall stunting, and ethylene evolution increased dramatically. At 9 DAT, plants died. Accumulation of NH4+ caused by GLA was mainly in the foliage and increased with time; that caused by exogenously supplied NH4+ was in roots and non-phytotoxic during the duration of the experiments.
If AOA or STS was added into nutrient solution with GLA at 25 mg/L, AOA delayed the appearance of toxicity and NH4+ accumulation but STS had no suppressive effects on their presence. AOA completely inhibited ethylene evolution during the experiment but STS did not low ethylene evolution by plant receiving GLA.
Effects of foliarly applied GLA and soil-applied GLA were compared. At 3 DAT, tomato plants sprayed with 1.5 or 3 mg GLA/kg soil started showing symptoms on top leaves. At 5 DAT, all foliarly treated plants became poisoned by GLA, and those receiving 1.5 or 3 mg GLA from soil started showing poisoning. Tomato plant growth was retarded slightly by GLA applied at more than 1.5 mg/plant during 5 days of growth.
Effect of degradation time of efficacy on GLA in soil was studied. At 4 days after transplanting, GLA induced toxicity symptoms and reduced biomass. GLA after 5-days degradation in soil caused higher shoot NH4 + accumulation than 10–20 days degradation.
Root-applied GLA under hydrophonics or soil conditions can cause foliar toxicity symptoms, foliar accumulation of NH4+, and ethylene evolution on tomato plants.