Bacteria as growth-promoting agents for citrus rootstocks

Abstract

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.

Endophytic bacteria associated with endangered plant Ferula sinkiangensis K. M. Shen in an arid land: diversity and plant growth-promoting traits

“…Among these positive strains, four strains showed strong antagonistic activities against all the three pathogenic fungi. Similar results were also reported in halophytes from Xinjiang (Wang, 2015), Allium sativum from Shanxi (Cui et al, 2008), and citrus rootstocks from Brazil (Giassi et al, 2016).…”

“…Equimolar concentration of Salkowski reagent (1 mL 0.5M FeCl 3 dissolved in 50 mL 35% HClO 4 ) was added to 1.5 mL of supernatant. The mixture was incubated for 30 min and the absorbance was measured in a spectrophotometer at 530 nm (Giassi et al, 2016). Medium without bacterial suspension was used as a control.…”

Phyllospheric Microbiomes: Diversity, Ecological Significance, and Biotechnological Applications

“…A cold-tolerant bacterial strain Exiguobacterium acetylicum 1P promotes wheat seedlings growth (Selvakumar et al 2010), Brevibacillus brevis improve the growth of cotton crop (Nehra et al 2016) and Bacillus spp. induce phosphate solubilization more efficiently when present as endophytes in citrus (Giassi et al 2016). The diazotrophic bacteria associated with phyllosphere gives benefits to the plant by fixing atmospheric nitrogen, solubilization of phosphorus (P), and utilization of available nutrients through its organic end product-mediated solubilization of rock phosphates (Mohammadi 2012;Kembel et al 2014;Mwajita et al 2013;Batool et al 2016;Lambais et al 2017).…”

Wine Lactic Acid Bacteria with Antimicrobial Activity as Potential Biocontrol Agents against Fusarium oxysporum f. sp. lycopersici

“…Taking all the results together would indicate that the bio protection exerted by the bacteria on the infected plants could be due to a combination of their antagonistic action on the pathogen and its phytostimulatory effect on the plant. The ability to stimulate plant growth has been studied in various bacteria, mostly in those that form the rhizosphere microbiota [39,42,43]. Microorganisms that enhance the growth and suppress diseases of the host plants are known as plant probiotics [44].…”