Carla da Silva Sousa

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.

Management of crotalaria and pigeon pea for control of yam nematode diseases

Management of plant-parasitic nematodes with the use of nematicides has not been recommended for small farmers that grow yam in the Northeastern region of Brazil, due to its high cost and residue toxicity. The use of plants with antagonistic effect to nematodes and green manure which improves soil chemical, physical and biological characteristics can be a viable and low cost alternative to control parasitic nematodes. This work aimed to evaluate the effect of crotalaria (Crotalaria juncea) and pigeon pea (Cajanus cajan) plants on the control of yam nematodes. Three experiments were carried out. The first was conducted under in vitro conditions to evaluate the nematostatic and nematicide effect of extracts from fresh and dry matter of the above ground parts of crotalaria, pigeon pea, and the combination of both. The second experiment was carried out under greenhouse conditions to evaluate the effect of soil amendment with crotalaria, pigeon pea, and the combination of both in the infectivity of Scutellonema bradys, using tomato plants as the host plant. The third experiment was conducted under field conditions to evaluate the effect of crotalaria, pigeon pea, and the combination of both, cultivated between yam planting rows and incorporated to soil surface, on yam nematodes. The aqueous extract obtained form fresh matter of crotalaria had a nematicide effect of 100% for S. bradys. Extracts from dry matter of both crotalaria and pigeon pea did not have any nematicide effect, but had a nematostatic effect. Incorporation of crotalaria to soil inhibited infectivity of S. bradys in tomato seedlings. These results showed that planting crotalaria alone or in combination with pigeon pea, between the yam planting rows, is an efficient method for controlling S. bradys and Rotylenchulus reniformis associated with yams. Crotalaria can be used for controlling these plant-parasitic nematodes in soil.

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.

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.

Bioconcentração de chumbo e micronutrientes em hortaliças cultivadas em solo contaminado

RESUMO - A crescente poluicao ambiental nas ultimas decadas vem tornando os metais pesados uma ameaca constante aos seres vivos. Entre estes, o chumbo (Pb) e um dos mais importantes, devido a quantidade de areas contaminadas e seus efeitos deleterios para saude humana. Este estudo objetivou avaliar a producao de biomassa e absorcao de micronutrientes por olericolas cultivadas em Espodossolo contaminado por Pb. Adicionalmente, a distribuicao de Pb entre as fracoes do solo e a relacao dessas fracoes com a disponibilidade do Pb para hortalicas foi tambem estudado. O experimento foi conduzido em blocos casualizados no esquema fatorial 5x3x4. Os tratamentos foram constituidos por cinco doses de Pb (0,0; 20; 50; 72 e 180 mg kg -1 de solo), tres especies vegetais (quiabo, cenoura e couve-manteiga) e quatro partes das plantas (raiz, caule, folha e partes comestiveis), sendo a ultima dose equivalente ao valor de investigacao para solos agricolas. De acordo com os resultados, o Pb promoveu reducao da materia seca nas plantas de cenoura e quiabeiro, enquanto nao influenciou a producao de biomassa da couve manteiga. O Pb afetou a concentracao de micronutrientes nos orgaos das hortalicas, sendo observado na cenoura reducao no teor de ferro enquanto na couve manteiga houve aumento do teor de Zn nas raizes. O Pb apresentou-se, preferencialmente, adsorvido a fracao materia orgânica. Plantas cultivadas em solo contaminado com a dose de investigacao estabelecida pelo CONAMA, alem de apresentarem desbalanco nutricional, podem tornar-se inadequadas ao consumo humano, devido ao elevado teor deste metal nas partes comestiveis. Palavras-chave: Hortalicas. Solo-poluicao. Plantas-efeito de metais pesados.

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 mudas de tomateiro em substrato orgânico inoculado e incubado com estreptomicetos

This work had the objective of evaluating the effect of inoculation and incubation of a potting soil with streptomycetes in growth promotion of tomato seedlings. The first experiment was conducted with four streptomycete isolates, with and without incubation for 20 days. The experimental design was entirely randomized with 15 replications, in a factorial squeme (5 x 2). The inoculation and incubation of the potting mix promotted a significant increase in plant height, root and shoot dry weight, and plant nutrient levels. In the second experiment, the inoculation with the two best isolates, in five different incubation periods (0, 15, 30, 45 and 60 days) was evaluated for growth of tomato seedlings in the same potting growth mix, using an entirely randomized experimental design with 8 replications and a factorial scheme 3 x 5. Forty three days was considered to be the best incubation period, suggesting that this may be the time necessary for the streptomycete isolates to colonize and act in the decomposition of the organic matter, improving nutrient uptake by the roots, and promoting plant growth.

ACTINOBACTÉRIAS E ADUBOS ORGÂNICOS NO MANEJO DO NEMATÓIDE Scutellonema bradys EM PLANTAS DE INHAME

This study aimed to evaluate the in vitro nematicidal effect of metabolites produced by actinobacteria strains, aqueous extracts from fresh and dry biomass of leguminous plants (sunn hemp, pigeon pea and Gliricidia sepium), liquid residue from sisal (Agave sisalana Perrine ex Engelm) and cassava (Manihot esculenta) to control Scutellonema bradys. Strains of actinobacteria and leguminous plants (sunn hemp, pigeon pea and gliricidia) were evaluated against S. bradys in yam plants. Strains AC-92, AC-12, AC-50 and AC-52 showed nematicidal effect against S. bradys under in vitro conditions. The aqueous extracts from the fresh biomass of sunn hemp, gliricidia and pigeon pea are more efficient than the aqueous extracts of the dry biomass of these plants for control of S. bradys under in vitro conditions. The liquid residues from sisal and cassava, in concentrations above 20 %, also have nematicidal effect against S. bradys under in vitro conditions. The green manures (sunn hemp, pigeon pea and gliricídia) and actinobacteria strains, singly or in combination, are effective for the management of S. bradys in yam crop.