Ana Cristina Fermino Soares

Characterization of streptomycetes with potential to promote plant growth and biocontrol

Studies with streptomycetes in biocontrol programs and plant growth promotion are presented as technological alternatives for environmental sustainable production. This work has the objective of characterizing six isolates of streptomycetes aiming the production of extracellular enzymes, indole acetic acid, capacity for phosphate solubilization, root colonization and growth under different pH and salinity levels. For detection of enzyme activity the isolates were grown in culture media with the enzyme substrates as sole carbon source. The root colonization assay was performed on tomato seedlings grown on 0.6% water-agar medium. Growth under different pH and salinity levels was evaluated in AGS medium with 1%, 1.5%, 2%, 2.5%, and 3% NaCl, and pH levels adjusted to 5.0, 5.5, 6.0, 6.5, and 7.0. All isolates produced the enzymes amylase, catalase, and lipase, as well as indole acetic acid. With one exception (AC-92), all isolates presented cellulolytic and chitinolytic activity, and only AC-26 did not show xylanolytic activity. The isolates AC-147, AC-95, and AC-29 were the highest producers of siderophores. The isolates AC-26 and AC-29 did not show capacity for phosphate solubilization. All isolates colonized tomato roots in vitro, and AC-92 grew under all pH and salinity levels tested. The streptomycetes tested were considered as potential biocontrol and plant growth promotion agents.

Soil streptomycetes with in vitro activity against the yam pathogens Curvularia eragrostides and Colletotrichum gloeosporioides

Yam (Dioscorea cayennensis Lam), an important crop in the Northeastern region of Brazil, is susceptible to the attack of several phytopathogenic fungi, such as Curvularia eragrostides (Henn.) Meyer and Colletotrichum gloeosporioides (Penz.), which cause leaf spot diseases. This work aimed to evaluate the effect of six actinomycete isolates (S. thermotolerans, S. griseus subsp. griseus, Streptomyces sp. N0035, S. purpurascens, and two isolates identified as Streptomyces sp.), as well as the effect of their secondary metabolites, on mycelium growth and spore germination of C. eragrostides and C. gloeosporioides, from yam plants, cultivar da Costa. Additionally, the chitinolytic activity of these actinomycete strains was determined in a minimum salt growth medium with chitin as the sole carbon source. There was significant interaction between the actinomycete isolates and the phytopathogenic fungi for spore germination and mycelium growth inhibition. Streptomyces sp. codified as AC 26 was more efficient in inhibiting spore germination of C. eragrostides, while S. thermotolerans and Streptomyces sp. N0035 were more efficient for C. gloeosporioides. Streptomyces sp. (AC 26) was the most efficient in inhibiting mycelium growth of both fungi, and the inhibitory effect was positively correlated to metabolite concentration. S. griseus subsp. griseus did not show chitinolytic activity and did not control mycelium growth of both fungi. The actinomycete strains evaluated in this study can be considered potential biological agents for controlling yam phytopathogenic fungi associated with leaf spot diseases.

Estreptomicetos no controle da meloidoginose em mudas de tomateiro

This work aimed to evaluate the effect of six streptomycete isolates on mortality, hatching, and control of Meloidogyne incognita on tomato seedlings. An assay was conducted in Elisa plates, with the addition of 200 µL of the streptomycete metabolites, along with 20 µL of suspension containing 25 second stage juveniles (J2) of M. incognita. The metabolites produced by Streptomyces griseus subsp. griseus caused mortality of 98.2% on M. incognita. A second assay was conducted with 3 mL of streptomycete metabolites and 25 eggs of M. incognita. The isolate N0035 of Streptomyces caused inhibition of 98.8% on hatching. In a third assay, potting mix was infested with suspension of the streptomycetes isolates and incubated for 30 days. Fifteen days after germination, tomato seedlings were inoculated with a suspension containing 2,000 J2 of M. incognita. Reductions of 68% in the number of galls per gram of roots and of 76.8% in the egg mass per gram of roots were observed on tomato seedlings grown in the potting mix inoculated with Streptomyces griseus subsp. griseus, compared to the control.

Production of streptomycete inoculum in sterilized rice

Actinomycetes are important plant disease control and growth promotion agents, which makes it necessary to develop technology to produce large quantities of inoculum for green-house and field work. The present study had the objective of evaluating the growth of several isolates of Streptomyces in sterile rice for inoculum production. The sterile rice was inoculated with isolates of S. thermotolerans, S. griseus subsp. griseus, Streptomyces sp. N0035, S. purpurascens, and Streptomyces sp., and incubated at 28 ± 2oC. Five days after its inoculation, mycelial growth and sporulation was observed for all Streptomyces isolates on the rice grains. Twelve days after incubation, the colonized rice was transferred to envelopes of dark brown paper and let to dry in an incubator at 30oC for three days. After drying, 1g of colonized rice was added to 200 mL of sterile distilled water and the number of spores was counted under a microscope with a Newbauer counting chamber. Spore production varied from 0.14 × 109 to 1.47 × 109 spores per gram of rice and differed among the Streptomyces species. Sterile rice can be an alternative substrate for low cost mass production of Streptomyces inoculum.

Control of tomato bacterial wilt through the incorporation of aerial part of pigeon pea and crotalaria to soil

The use of organic matter that improves the physical, chemical and biological soil properties has been studied as an inducer of suppressiveness to soilborne plant pathogens. The objective of this work was to evaluate the effect of different sources and concentrations of organic matter on tomato bacterial wilt control. Two commercially available organic composts and freshly cut aerial parts of pigeon pea (Cajanus cajan) and crotalaria (Crotalaria juncea) were incorporated, in concentrations of 10, 20 and 30 % (v/v), into soil infested with Ralstonia solanacearum. The soil with the fresh organic matter of pigeon pea and crotalaria was incubated for 30 and 60 days before planting. Tomato seedlings of cv. Santa Clara were transplanted into polyethylene bags with 3 kg of the planting substrate (infested soil + organic matter). The wilting symptoms and percentage of flowering plants were evaluated for 45 days. All evaluated concentrations with incorporation and incubation for 30 days of aerial parts of pigeon pea and crotalaria controlled 100% tomato bacterial wilt. With 60 days of incubation, only the 10 % concentration of pigeon pea and crotalaria did not control the disease. These results suggest that soil incorporation of fresh aerial parts of pigeon pea and crotalaria is an effective method for bacterial wilt control.

Diazotrophic bacteria associated with sisal (Agave sisalana Perrine ex Engelm): potential for plant growth promotion

AimsIn the semi-arid region of Bahia State, Brazil, sisal (Agave sisalana Perrine ex Engelm) has been cultivated for fibre production for several decades without the use of chemical fertilizers. The contribution of biological nitrogen fixation (BNF) to this crop and the occurrence of diazotrophic rhizosphere, epiphytic or endophytic bacteria have not been investigated. The aims of this work were to study the occurrence and diversity of diazotrophic bacteria in rhizosphere soil, root and leaf tissues of sisal plants from this region, as well as to test their potential for plant growth promotion.MethodsBurk’s nitrogen free semi-solid medium was used for isolation and the MPN method was used for quantification of diazotrophic bacteria. BOX-A1R PCR and 16S rRNA sequence analyses were performed to study the diversity of bacterial isolates harboring the nifH-gene. Six isolates were selected for growth promotion of cucumber plants.ResultsA high diversity of BNF bacterial isolates was observed in sisal plants and rhizosphere soil. Bacterial populations were higher in roots, followed by soil and sisal leaves. Burkholderia, Leifsonia and Paenibacillus were the predominant genera. All isolates tested were able to promote cucumber growth.ConclusionsThis study showed that sisal-associated diazotrophic bacteria are diverse and may be further exploited to promote plant growth.

Ocorrência e atividade de fungos micorrízicos arbusculares em plantios de eucalipto (eucalyptus sp.) no litoral norte da Bahia, Brasil

In recent decades, alternative technologies have been studied in order to make the cultivation of eucalyptus more economical and sustainable. Among these, the mycorrhizal associations deserve mention because of the many benefits they provide to host plants. Mycorrhizal fungi (AMF) form mutualistic association with plant roots, promoting greater uptake of nutrients to the host, which in turn yields products of photosynthesis to the fungus. With the establishment of the association, the plants become more resistant to adverse conditions such as nutrient-poor soil, low pH, high temperature, water stress, decreased microbial activity, among other biotic and abiotic stresses. This study aimed to evaluate the occurrence and activity of mycorrhizal fungi in eucalypt plantations used commercially by Copener Florestal Ltda. northern coast of Bahia. A high variability in the density of spores (36.2 to 203.2 spores in 50 g of soil), mycorrhizal colonization (10.6 to 57.8%) and levels of easily extractable glomalin and total (0.34 to 1.92 mg g-1 soil and 0.48 to 3.88 mg g soil-1) in plantations. The results of this study showed that although the clones showing susceptibility to mycorrhizal infection in field conditions, variations in soil characteristics affect the ecological aspects of mycorrhizal fungi in plantations of eucalyptus Copener Florestal Ltda. northern coast of Bahia.

Five egg-laying queens in a single colony of brazilian stingless bees (Melipona scutellaris Latreille

Polygyny, characterized by the presence of several egg-laying queens, is considered as a temporary colony status. In stingless bees it is rarely observed. This paper reports the first case of natural polygyny in Melipona scutellaris colony, with five egg-laying queens.

Fungos micorrízicos arbusculares no crescimento e nutrição de mudas de jenipapeiro

Alguns trabalhos tem demonstrado que a inoculacao de fungos micorrizicos arbusculares (FMA) na producao de mudas apresenta grande potencial para o desenvolvimento de um cultivo racional e eficiente de mudas de fruteiras. O objetivo neste trabalho foi avaliar a inoculacao de fungos micorrizicos arbusculares no crescimento e nutricao de mudas de jenipapeiro (Genipa americana L.). O experimento foi conduzido em blocos casualizados, avaliando-se seis especies fungicas: Glomus clarum, Glomus etunicatum, Glomus manihots, Gigaspora albida, Acaulospora scrobiculata e Scutellospora heterogama, com dez repeticoes. As especies A. scrobiculata, G. clarum e G. etunicatum colonizaram mais intensamente o sistema radicular e promoveram melhor desenvolvimento das mudas de jenipapeiro quando comparados a G. manihots e G. albida. O fungo G. etunicatum destacou-se, promovendo incrementos na altura (44,4%); no diâmetro do caule (63,6%); na producao de biomassa seca na parte aerea (288,8%), nas raizes (248,7%) e na area foliar (315,7%) em comparacao as mudas controle. Com excecao de Mn e Fe, mudas inoculadas apresentaram teores de nutrientes superior as mudas controle. As mudas que receberam inoculo de S. heterogama apresentaram crescimento e teor de nutrientes similares aos das mudas controle. A colonizacao micorrizica correlacionou-se positivamente com os teores de N, P, K, Mg e Cu e negativamente com os teores de Fe e Mn nas folhas das mudas de jenipapeiro. O jenipapeiro e uma planta responsiva aos FMA e a inoculacao beneficiou o crescimento e a nutricao das mudas.

Produção de biomassa de erva-cidreira [Lippia alba (Mill.) N.E.Br.] sob adubação com composto de capim elefante inoculado e sem inoculação de actinomicetos

L. alba is a species of the family Verbenaceae widely used by the Brazilian population, because of the soothing, gentle antispasmodic, analgesic, expectorant, sedative, anxiolytic and smoothly. For the implementation of the experiment produced organic compound of elephant grass (Pennisetum purpureum Shum.) + manure at 70% plant material and 30% manure, uninoculated and inoculated with the actinomycete Streptomyces genus, AC16, AC26, AC92 and AC103. The compounds were placed in polyethylene bags containing 10.0 kg of soil added in a proportion equivalent to 20 t ha-1 and re-apply after the first harvest. The harvests of the shoots were taken at 75 and 165 days after transplantation. The roots were harvested after the second harvest. Dealing with organic fertilization promoted the average increase in biomass production of lemon grass 184, 83, 125, 115 and 122% for the dry stem biomass (MSPA) in the first harvest, second harvest of MSPA, total shoot biomass (MSTPA), dry biomass of the root (MSR) and the total crop biomass (MST), respectively, compared with the control, but no effect of inoculation of actinomycetes in compost. Under the conditions of this study was conducted, it was concluded that the organic compound fertilizer with elephant grass positively influenced the production of dry biomass of L. alba, but the injection of the compounds of the actinomycetes, without influence.