Growth promoting bacteria are a potential option for sustainable cultivation with lower costs, among them Burkholderia ambifaria, whose importance is mainly due to the endophytic root colonization capacity. The objective of this work was to evaluate the effect of the inoculation of growth promoting bacteria in corn plants, in vitro and in greenhouse, with different levels of nitrogen fertilization. The PIONEER® 30F53 YH maize genotype was inoculated with Burkholderia ambifaria, with 106 CFU per seed, in 12-liter polyethylene pots, filled with commercial substrate, prepared with the different nitrogen contents (N), resulting in treatments with different doses of fertilization, associated or not with bacterial inoculation. After 30 and 45 days, it was evaluated: growth promotion, epiphytic and endophytic population and nitrogen accumulation. In the in vitro experiment, inoculated seeds were cultured in test tubes containing culture medium with absence and presence of nitrogen, evaluated after 7 days. The data were submitted to analysis of variance and the means were compared by the Tukey test at 5% of probability and regression. Increased nitrogen doses in inoculated plants resulted in better morphological parameters at 45 days. In vitro bacterial inoculation, in vitro, influenced the accumulation of fresh weight of shoot, root growth and development of root hair. The endophytic potential and the accumulation of nitrogen were higher in the absence of nitrogen, but lower than the absence of bacteria and the presence of nitrogen.
The objective was to evaluate the incidence and severity of anthracnose on soybean plants and seedlings treated with coco-grass extract and 2,4-D. The samples of Colletotrichum sp. were distributed into petri dishes containing BDA medium. After replicate, the dishes were sealed with a plastic film and placed for growth in the BOD chamber at 27 ºC for one week, then performed a new replication. Ten soybean seeds were put into plastic boxes fully filled with autoclaved sand, using six replicates. Treatments consisted of spraying a solution of coco-grass extract or 2,4-D at concentrations of 0%, 25%, 50%, 75% and 100% on soybean seedlings and plants, under laboratory and greenhouse conditions. An increase in the number of injured plants according to the increase of the concentration of the extract, where a smaller but not insignificant number of plants injured in the treatment 25% of coco-grass and the maximum value of injured plants in the highest concentration (100%) of this treatment. Highlighted Conclusion Auxin derived from coco-grass extract causes a greater susceptibility of soybean to anthracnosis. Soybean is largely cultivated on all regions of the world, it reached a production of 334,894,085 Mg in the crop year of 2016, being United States, Brazil and Argentina the largest producers in the world (FAO 2018). The role of soybeans in the Brazilian industry is also recognized, according to MAPA (2015), about 5.8 million Mg of edible oil are produced per year, 23.5 million Mg of protein meal, out of a total of 30.7 million tons of soybean that the industry transforms in byproducts. The search for alternative methods that may increase productivity in some way, such as investment in soil fertility, use of crop rotation, use of irrigation, control of pathogens and use of plant regulators are essential for the continuity of the agricultural market, however, there are cases where the use of plant regulators makes the plant more susceptible to the action of the pathogen in its cell. The use of auxin in a plant, whether in biological or synthetic form, is an example of this, its use cases a series of effects, such as cell elongation and differentiation, membrane permeability impairment, increase in respiration process, increase in synthesis of messenger RNA and increase in the synthesis of proteins, such factors are responsible for the better development of the plant (Agrios 1997). However, these processes make the cell wall more susceptible, helping the fungus to penetrate the plant cells more efficiently, since it is no longer so hard. Anthracnose is one of the major fungal diseases of economic interest of soybeans, directly attacking the pods, causing them to fall and consequently a fall in production (Kimati 2005). It is known that some pathogens are responsible for increasing the concentrations of auxin in plants, which in turn leads to a greater susceptibility of the cell wall of the plants to the enzymes that the pathogens produce, thus facilitating their contamination (Llorente et al. 2008).
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