Rizobactérias multifuncionais na mitigação do déficit hídrico e da brusone foliar em arroz de terras altas
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2021-02-26
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Universidade Federal de Goiás
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Rice is a staple food for more than half of the world population and is the main source of carbohydrate. Its cultivation is constantly challenged by biotic and abiotic stresses, among which the water deficit and the blast (Magnaporthe oryzae) stand out. The use of plant growth promoting rhizobacteria (RPCP), proves to be a more sustainable alternative aiming at an ecologically healthy control. The objective of the research was to characterize 9 rhizobacteria isolates, select them for their resistance to high osmotic potentials, test their effects on germination and initial development of rice seedling roots in vitro and evaluate them for mitigation of leaf blast and water deficit. They were divided into five trials. 1. The nine rhizobacteria isolates divided into Burkholderia pyrrocinia (BRM 32113) two isolates from Serratia sp. (BRM 32114 and BRM 63522) and two from Serratia marcescens (BRM 63521 and BRM 63523); Bacillus thuringiensis (BRM 32110), Bacillus cereus (BRM 32109), Pseudomonas fluorescens (BRM 32111) and Pseudomonas sp. (BRM 32112) were characterized for the production of extracellular enzymes, siderophores, biofilm, ACC deaminase enzyme, indolacetic acid (AIA) and phosphatase, in a completely randomized design, and three replications. 2. The rhizobacteria isolates were grown in liquid culture medium supplemented with seven different concentrations of PEG-6000 in a completely randomized design, and twelve replications. The growth rate was determined and viable cells were quantified. 3. Three isolates were selected and used to treat the seeds of the cultivar BRS Esmeralda of upland rice. The seeds were sown in a solid culture medium containing the seven concentrations of PEG-6000 in a completely randomized design, with six replications. Initial seedling root development was evaluated with the aid of a scanner and the WinRhizo Pro 2012b program. 4. The same three isolates previously selected were tested for antagonistic ability to M. oryzae, in Petri dishes containing culture medium enriched with seven different concentrations of PEG-6000 in a completely randomized design, in three replications. The effect of the bacteria was determined through the colony diameter of each treatment. 5. In greenhouse conditions, seeds of the cultivar BRS Esmeralda, treated with the isolate BRM 32111, were sown in plastic trays containing 3 kg of soil with necessary fertilization. At 15 days after planting, the leaves were sprayed with the same isolate and at 21 days they were subjected to four days of water deficit. Gas exchanges were evaluated at the end of this period. At 26 days, the plants were inoculated with a conidia suspension of M. oryzae and it was possible to evaluate the Area Below the Disease Progress Curve (AACPD). The isolates BRM 32110, BRM 32111 and BRM 63523 demonstrated greater resistance to high osmotic pressures and showed production of extracellular enzymes, siderophores, biofilm, AIA, ACC deaminase enzyme and phosphate solubilization. The three rhizobacteria tested continued to demonstrate antagonistic effects to M. oryzae. For initial seedling development in vitro, the three isolates were promising at high osmotic pressures. The use of rhizobacteria stimulated the increase in length and root area, and also stimulated the greater development of lateral roots, mitigating the effects of water deficit, expanding the contact area even further. For length and total root surface area (CTR and AST) there is an increase of, 107 and 157% (BRM 32111), 58 and 55% (BRM 32110) and 68 and 70% for (BRM 63523). In length and area of very thin roots (CRMF and ASRMF) showed greater increase when conditioned to stress by PEG, with T3 being the biggest increase in relation to the control, 150 and 302% (BRM 32111), 65 and 112% (BRM 32110) and 99 and 116% (BRM 63523). In the greenhouse, the use of BRM 32111 showed an increase in relation to photosynthesis (A), transpiration (E), stomatal conductance (gs) and internal concentration of (Ci) carbon for both water conditions (irrigated and stressed), for efficiency in water use (A / E) and rubisco carboxylation rate (A / Ci) the bacteria showed a greater effect on unstressed rice. The same isolate still suppressed leaf blast severity. The 9 isolates used showed potential in mitigating water deficit and suppression of leaf blast, highlighting BRM 32111 as an alternative in biological control aiming at a more sustainable agriculture.
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MENDONÇA, S. M. Rizobactérias multifuncionais na mitigação do déficit hídrico e da brusone foliar em arroz de terras altas. 2021. 89 f. Dissertação (Mestrado em Agronomia) - Universidade Federal de Goiás, Goiânia, 2021.