Bacillus megaterium 501RIF as antidot of herbicide prometryn in crops of oats and corn

The application of the herbicide prometryn (4,6-bis-(isopropylamino)-2-methylthio-1,3,5-triazine) for weed control, makes many agrotechnological and ecological problems due to relatively higher persistence in the environment. It is well known that many microorganisms are capable of decomposing the herbicide. There has been some attempt to use microorganisms for bioremediation of soils. Bacillus megaterium is of particular interest because it produces many physiologically active substances that increase the efficiency of photosynthesis, stimulates growth, and accelerates the formation of plants reproductive organs, as well as decomposes some pesticides. In this article, we present new data on the effect of B. megaterium 501rif inoculation upon plant resistance to the herbicide prometryn. There was shown that the B. megaterium 501rif brings down the phytotoxicity of the herbicide and decomposes it in the rhizospheres of oats and corn. The purposes of the work were to study the survival rate of B. megaterium 501rif in the rhizosphere of oats and maize and to estimate its effect on plant resistance to prometryn, as well as ability to effectively decomposition of this herbicide in the soil. B. megaterium 501rif was cultured on a rotary shaker for 48 hours at 30 °С, 140 rpm. The bacterial titer was 5½108 CFU/ml and included at least 90 % of the alive cells. Seeds of oats ( Avena sativa L.) cultivar Pobeda and maize ( Zeal mays L.) cultivar Ross 199 MV were inoculated with a 2-days liquid culture of B. megaterium 501rif and were sown in vegetative pots. The soil was soddy-podzolic, medium loam, with an organic matter content of 2.3 %, pH 5.8. An aqueous suspension of wetting powder of prometryn (Panama Agrochemical Inc., Panama) was applied in the quantity of 0.12, 0.22, 0.67, and 1.23 mg/kg in the experiment with oats and 3.4, 6.8 and 20.4 mg/kg in the experiment with corn. In last case there was a variant with prometryn (6.5 mg/kg) but without plants. Plants were grown in the light chamber Phytos-4 (PHYTOS, Russia) at a temperature of 22-25 °C. The dry weight of plants, the quantity of prometryn in the soil, and the number of bacteria in the rhizosphere were determined 30 days after the sprouts appeared. The field experiment was conducted in the experimental field of the All Russia Institute for Agricultural Microbiology (Pushkin, Leningrad region). The soil was soddy-podzolic medium loam, with an organic carbon content of 2.3 %, pH 5.6. The herbicide prometryn was applied to the soil at a dose of 500 mg/m2, which approximately corresponded to 1,5 mg/kg. The seeds of corn were not inoculated in the control. The dry weight of plants and the quantity of herbicide in the soil were determined 30 days after the sprouts appeared. B. megaterium 501rif took root well in the rhizospheres of oats and corn. The number of bacteria were 300 to 500 thousand CFU/g soil, and from 58 to 80 % of them were physiologically active cells. The weight of oats increased by 11 %, corn - by 20 %, when seeds were inoculated with B. megaterium 501rif culture. The resistance of plants to herbicide significantly increased and quantity of prometryn decreased 2-3-fold in the soil under oats, and 20-fold under corn. In the field experiment the weight of the corn plant was 11.6 % higher, while the herbicide quantity in the soil was 3 times lower than in the control. We suppose that the higher resistance of plants inoculated with bacteria to the herbicide is due to a positive effect of their metabolites, in particular poly-beta-hidroxibutyrate, produced by bacteria as well as active participation of bacteria in the degradation of the herbicide. Thus, B. megaterium 501rif like an antidote takes off the phytotoxic effect of the herbicide on plants and increases their productivity. Corn, when inoculated with bacteria, decomposes prometryn effectively and can be