Scientists from Embrapa Environment (SP) evaluated the potential of functional bacterial isolates to promote the growth of
tomato plants cultivated under soil saline stress conditions. From 154 strains of bacilli initially studied, four were selected and showed increase in height, root and shoot weight, chlorophyll content and stem diameter. In addition, they managed to reduce the severity of Fusarium wilt in tomatoes by more than 50%. Second the researcher Wagner Bettiol, the rate of salinization of soils has expanded globally, causing food safety problems in several countries. Furthermore, salt stress occurs naturally in arid and semiarid regions. The salinization of soils negatively affects photosynthesis, nutrient absorption, transpiration , protein synthesis and hormonal regulation, resulting in reduced plant growth. Carlos Medeiros, that at the time of the study he was a Master’s student at Unesp/Botucatu under the supervision of Bettiol , explains that the research was divided into three phases. In the first, biochemical tests were carried out, which evaluated the production of plant hormones, phosphorus solubilization, nitrogen fixation and the production of some important compounds for plant development. These tests were carried out at the “Raquel Ghini” Environmental Microbiology Laboratory of Embrapa Meio Ambiente, exposing 154 bacilli isolates to conditions of increased salt content. “We used six biochemical tests to make this first selection. Several bacilli isolates showed positive responses, but those that showed at least four positive responses to the six tests for the following phases of the studies were selected”, informs Medeiros. Then, these four isolates selected in the laboratory were evaluated in plants from tomato grown in a greenhouse. “We started testing the isolates directly on plants developed under conditions with and without salt stress to assess several characteristics related to plant growth”, he explains. The studies analyzed the increase in height, weight of roots and shoots of the plants, as well as the chlorophyll content of the leaves and the stem diameter of tomato plants, important parameters in this case. After this phase, the isolates were evaluated in the control of wilt Tomato Fusarium. “In addition to the efficiency in controlling wilt, we analyzed three enzymes that are directly related to the induction of plant resistance to the pathogen and also to proline, an amino acid specifically aimed at protecting against salt stress”, says Medeiros. Details of the results, which were part of Carlos Medeiros’ master’s thesis, are published in
Biological product in sight
Among the selected strains, the most efficient was one of Bacillus velezensis, a species that has stood out in studies related to the biological control of diseases of plants, explains Bettiol. “This isolate reduced the severity of Fusarium wilt by more than 50%”, he highlights. After All the experimentation and data analysis, Medeiros emphasizes: “We came to the conclusion that the isolates established an interaction with the plants, which triggered different defense mechanisms”. According to him, this association with the plant is essential for the bacilli isolates to have controlled the disease caused by Fusarium, increased plant growth and tolerance to salt stress, suggesting that they can be used beneficially in biological control in agriculture. “But it is important to note that these results vary from isolated to isolated, which demonstrates that such characteristics are intrinsic to certain microorganisms. Not all microorganisms of the same genus or species will show the same behavior in plants or in any other situation where you want to use them, which shows the importance of testing and experimenting to understand the specificity of each one and select the most suitable”, highlights the researcher. “For the development of a biological product based on microorganisms, whether for disease control, growth promotion or to alleviate the salt stress of plants, the first step is the isolation and selection of microorganisms”, says Bettiol. In the study, part of the nearly 500 bacilli isolates obtained during his doctorate in 1984 were used in Esalq/USP, with the assistance of the Foundation for Research Support of the State of São Paulo ( FAPESP) and Finep.
The multiplication of bacilli, under different fermentation conditions, is already being carried out in the laboratory, in parallel with new growth promotion tests. The goal is to develop a biological product based on these functional bacteria.
In the case of fusariosis control, the method used was the application of bacteria directly to the soil. “We cultivated the bacillus in a culture medium, diluted it and applied it via irrigation on the plant’s neck”, explains Medeiros. For saline stress, the form of application was the same, via irrigation.
The Fusarium Wither The wilt of Fusarium of the tomato occurs in most regions of the world where the fruit is grown. It is one of the worst diseases of this crop and can result in productivity losses of up to 80% in susceptible varieties. It occurs at any time or stage of development, most often in adult plants, and can make cultivation unfeasible in certain regions or times of the year.
The first symptoms are the yellowing of the older leaves, which gradually wither and present marginal or total limb necrosis, accompanied by wilting of the upper leaves in the hottest hours of the day.
With the progress of the disease, the yellowing increases until reaching the younger leaves as well. In this condition, the fruits do not develop, ripen still small or fall prematurely and the diseased plants show reduced growth and may die after having their vascular system completely compromised by the pathogen. Source: Embrapa
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