-Rhizosphere and phylloplane yeasts are able to produce phytohormones, acting as potential plant growth promoters. The aim of this study was to analyze the production of indole acetic acid (IAA) by yeasts using variations in the culture conditions. The yeasts evaluated were Rhodotorula mucilaginosa and Trichosporon asahii, which were cultivated in a potato broth medium with 20 g/L of glucose or sucrose as the carbon source. The cultivation was carried out at 22°C, 25°C or 30°C, and the initial pH was adjusted to 3.0, 4.5 or 6.0. The cultures were analyzed using a colorimetric technique with Salkowski reagent. The cell count was determined in all of the conditions. The results for T. asahii showed that IAA production with sucrose was superior at pH 6.0, and that with glucose was superior at pH 4.5. These results indicate an association between the carbon source and medium pH. Rh. mucilaginosa (2F32) presented a high IAA production when compared with T. asahii (3S44 and 4C06) or even with other microorganisms referenced in the literature. The highest production (0.655 g/L) was obtained at pH 6.0 with glucose as the carbon source. Variations in the culture conditions did not affect the cell growth of the yeasts.
Yeasts isolated from sugar cane and maize rhizosphere, leaves and stalks were screened against the phytopathogenic molds Colletotrichum sublineolum and Colletotrichum graminicola, both causal agents of the anthracnose disease in sorghum and maize, respectively. Strains identified as Torulaspora globosa and Candida intermedia were able to inhibit the mold growth, with the first species also exhibiting killer activity. No previous report on the application and potentiality of these yeasts as biocontrol agents were found neither the killer phenotype in Torulaspora globosa.
Trichoderma fungi are considered relevant plant growth promoters for increasing the efficiency in the use of nutrients, as well as acting as biological control agents. This study aimed to select Trichoderma spp. isolates with potential for phosphate solubilization and their application as growth promoters in interaction with homeophatic preparations, in cherry tomato. Among 16 Trichoderma spp. isolates obtained from soils of organic tomato growing areas tested in vitro, together with a commercial product (Trichodermil®), two of them showed the ability for indole-3-acetic acid production and phosphate solubilization. The Trichoderma “R” had the highest mycelial growth speed index and presented twice as much spores than the commercial product. An in vivo experiment was also conducted in a greenhouse, in order to observe the potential of Trichoderma spp. isolates and homeophatic preparations on the cherry tomato growth promotion, using a randomized block experimental design, in a 4 x 3 factorial arrangement, with three Trichoderma isolates and two homeopathic preparations (Phosphorus 6CH and Carbo vegetabilis 6CH) + treatment without homeopathic preparation. The leaf area and dry mass of leaves and roots were determined. It was possible to observe that the isolate “R”, identified as Trichoderma asperellum, was effective in the cherry tomato growth promotion, while the homeopathic preparations applied did not show any effect.
Among soil microorganisms, one group stands out as beneficial to agricultural activities: a plant growth-promoting rhizobacteria (PGPM). These microorganisms support plants through phytohormone production, nutrient provision and plant health maintenance. Among these PGPM, yeasts have a high potential, which is still not very well known.This study aimed to evaluate the effect of inoculation with the rhizosphere yeast Torulaspora globosa (strain 5S55) on development of lettuce (cv. Crocantela). The first research consisted of inoculating seeds with yeast (100 cells/seed), and inoculating seeds, 7 and/or 15 days after emergence (DAE) (1x106 cells/plant). The second one consisted of transplanting seedlings from the first experiment to field. Inoculation of seeds and seedlings provided a significant increase of seedling root dry mass; we observed the significant increase of 27% in productivity of lettuce under field conditions, of shoot fresh mass and a raise of number of leaves per plant. However, studies on inoculation methods, inoculum formulation, cell concentration are essential to optimize the results in growth promotion and to establish technology.
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