The microbial community plays an essential role in maintaining the ecological balance of soils. Interactions between microorganisms and plants have a major influence on the nutrition and health of the latter, and growth-promoting rhizobacteria can be used to improve plant development through a wide range of mechanisms. Therefore, the objective of the present study was to evaluate bacteria as growth-promoting agents for citrus rootstocks. A total of 30 bacterial isolates (11 of Bacillus spp., 11 actinobacteria, and 8 lactic acid bacteria) were evaluated in vitro for indoleacetic acid production, phosphate solubilization, and nitrogen (N) fixation. In vivo testing consisted of growth promotion trials of the bacterial isolates that yielded the best results on in vitro tests with three rootstocks: Swingle citrumelo [Citrus×paradisi Macfad cv. Duncan×Poncirus trifoliata (L.) Raf.], Sunki mandarin (Citrus sunki Hort. ex Tan), and rangpur (Citrus×limonia Osbeck). The parameters of interest were height, number of leaves, stem diameter, shoot and root dry mass, and total dry mass at 150days after germination. The results showed that most bacterial isolates were capable of IAA production. Only one lactic acid bacterium isolate (BL06) solubilized phosphate, with a high solubilization index (PSI>3). In the actinobacteria group, isolates ACT01 (PSI=2.09) and ACT07 (PSI=2.01) exhibited moderate phosphate-solubilizing properties. Of the Bacillus spp. isolates, only CPMO6 and BM17 solubilized phosphate. The bacterial isolates that most fixated nitrogen were BM17, ACT11, and BL24. In the present study, some bacteria were able to promote growth of citrus rootstocks; however, this response was dependent on plant genotype and isolate. Bacillus spp. BM16 and CPMO4 were able to promote growth of Swingle citrumelo. In Sunki mandarin plants, the best treatment results were obtained with BM17 (Bacillus sp.) and ACT11 (actinobacteria). For Rangpur lime rootstock, only BM05 (Bacillus sp.) was able to promote increase in two parameters assessed, height and number of leaves. When the bacterial isolates were used in mixture there was not promoted growth of plants on rootstocks. This fact may be associated with the different mechanisms of action of each bacteria involved or with the presence of competition among the microorganisms of the mixture.
R E S U M OObjetivou-se indicar, neste trabalho, dentre alguns fungicidas químicos recomendados para o controle das doenças em feijoeiro, quais seriam mais adequados considerando-se os fungos micorrízicos arbusculares nativos como bioindicadores. O experimento foi conduzido em casa de vegetação sob condições controladas com sete tratamentos e cinco repetições, sendo água, azoxistrobina, piraclostrobina, tebuconazol + trifloxistrobina, trifloxistrobina, óxido cuproso e mancozebe. Os parâmetros avaliados foram colonização micorrízica, número de esporos viáveis, teores foliares de N, P e K, massa seca da raiz e da parte aérea e massa fresca de vagem. Azoxistrobina, tebuconazol + trifloxistrobina e trifloxistrobina não causaram diferença significativa na colonização de fungos micorrízicos arbusculares nativos na quantidade de esporos no solo nem nos teores de N, P e K foliar em relação ao controle. Piraclostrobina, óxido cuproso e mancozebe inibiram a colonização micorrízica em referência ao controle. Os fungicidas à base de azoxistrobina, tebuconazol + trifloxistrobina ou trifloxistrobina podem ser usados para o controle das principais doenças do feijoeiro sem inibir a atividade dos fungos micorrízicos arbusculares nativos. Selection of fungicides aiming preservation of the indigenous arbuscular mycorrhizal fungi in the common bean cultivation A B S T R A C TThe aim of this study was to point out which chemical fungicides, from the usually recommended ones, would be more suitable to control common beans diseases, considering indigenous arbuscular mycorrhizal fungi (AMF) as bio-indicator. The experiment was conducted under controlled greenhouse conditions and was comprised by seven treatments and five plots of repetition each one. The treatments were: water, azoxystrobin, pyraclostrobin, tebuconazol + trifloxystrobin, trifloxystrobin, cuprous oxide and mancozebe. AMF root colonization index, amount of viable spore, leaf NPK content, shoot and root dry weight and pod fresh weight were assessed. Azoxystrobin, tebuconazol + trifloxystrobin and trifloxystrobin did not affect significantly the AMF root colonization, amount of spore and leaf NPK content, when compared with control. Pyraclostrobin, cuprous oxide and mancozeb inhibited the AMF root colonization. Using the azoxystrobin, tebuconazol + trifloxystrobin and trifloxystrobin are the best options to control the common bean main diseases without inhibiting AMF activities and its benefits. Palavras-chave:Phaseolus vulgaris fungos simbiontes controle químico
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