Isolation and Characterization of Plant Growth-Promotion Diazotrophic Endophytic Bacteria Associated to Sugarcane (Saccharum officinarum L.) Grown in Paraíba, Brazil

Abstract: Sugarcane is an important Brazilian commodity, being usually cultivated in soils with low natural fertility. This study aimed to isolate diazotrophic endophytes from sugarcane tissues and evaluate the morphological and physiological characteristics of their colonies as well as their plant growth-promoting (PGP) traits in select diazotrophic endophytic bacteria. Fifty-six bacterial isolates were identified in the sugarcane tissues, and these isolates presented distinct morphological and physiological traits. A total of thirty-five bacterial isolates were biochemically evaluated. Overall, Bacillus was the dominant genus. Isolates of Methylobacterium spp. and Brevibacillus agri were present only in leaves, while Herbaspirillum seropedicae occurred only in stems. Except to IPA-CF45A, all isolates were nitrogenase positive. All endophytes exhibit production of indol 3-acetic acid. Over 50% of endophytes solubilize phosphate, release N-acyl homoserine lactones, and present the activity of 1-aminocyclopropane-1-carboxylic acid deaminase, catalase, lipase and protease. The network analysis showed that isolates belonged to Burkholderia, Herbaspirillum, and Methylobacterium interact with Bacillus. Bacterial endophytes exhibited distinct morphological, physiological, and PGP traits that are useful for sustainable agriculture, highlighting the isolates IPA-CC33, IPA-CF65, IPA-CC9 and IPA-CF27. Further studies on the effects of these diazotrophic endophytes and their potential for providing microbial inoculants for improving sugarcane fields will provide valuable information to maintain the sustainability and environment quality.

Changes induced by co-inoculation in nitrogen-carbon metabolism in cowpea under salinity stress

ABSTRACT To mitigate the deleterious effects of abiotic stress, the use of plant growth-promoting bacteria along with diazotrophic bacteria has been increasing. The objectives of this study were to investigate the key enzymes related to nitrogen and carbon metabolism in the biological nitrogen fixation process and to elucidate the activities of these enzymes by the synergistic interaction between Bradyrhizobium and plant growth-promoting bacteria in the absence and presence of salt stress. Cowpea plants were cultivated under axenic conditions, inoculated with Bradyrhizobium and co-inoculated with Bradyrhizobium sp. and Actinomadura sp., Bradyrhizobium sp. and Bacillus sp., Bradyrhizobium sp. and Paenibacillus graminis, and Bradyrhizobium sp. and Streptomycessp.; the plants were also maintained in the absence (control) and presence of salt stress (50 mmolL-1 NaCl). Salinity reduced the amino acids, free ammonia, ureides, proteins and total nitrogen content in nodules and increased the levels of sucrose and soluble sugars. The co-inoculations responded differently to the activity of glutamine synthetase enzymes under salt stress, as well as glutamate synthase, glutamate dehydrogenase aminating, and acid invertase in the control and salt stress. Considering the development conditions of this experiment, co-inoculation with Bradyrhizobium sp. and Bacillus sp. in cowpea provided better symbiotic performance, mitigating the deleterious effects of salt stress.

Antioxidant response of cowpea co-inoculated with plant growth-promoting bacteria under salt stress

Abstract Soil salinity is an important abiotic stress worldwide, and salt-induced oxidative stress can have detrimental effects on the biological nitrogen fixation. We hypothesized that co-inoculation of cowpea plants with Bradyrhizobium and plant growth-promoting bacteria would minimize the deleterious effects of salt stress via the induction of enzymatic and non-enzymatic antioxidative protection. To test our hypothesis, cowpea seeds were inoculated with Bradyrhizobium or co-inoculated with Bradyrhizobium and plant growth-promoting bacteria and then submitted to salt stress. Afterward, the cowpea nodules were collected, and the levels of hydrogen peroxide; lipid peroxidation; total, reduced and oxidized forms of ascorbate and glutathione; and superoxide dismutase, catalase and phenol peroxidase activities were evaluated. The sodium and potassium ion concentrations were measured in shoot samples. Cowpea plants did not present significant differences in sodium and potassium levels when grown under non-saline conditions, but sodium content was strongly increased under salt stress conditions. Under non-saline and salt stress conditions, plants co-inoculated with Bradyrhizobium and Actinomadura or co-inoculated with Bradyrhizobium and Paenibacillus graminis showed lower hydrogen peroxide content in their nodules, whereas lipid peroxidation was increased by 31% in plants that were subjected to salt stress. Furthermore, cowpea nodules co-inoculated with Bradyrhizobium and plant growth-promoting bacteria and exposed to salt stress displayed significant alterations in the total, reduced and oxidized forms of ascorbate and glutathione. Inoculation with Bradyrhizobium and plant growth-promoting bacteria induced increased superoxide dismutase, catalase and phenol peroxidase activities in the nodules of cowpea plants exposed to salt stress. The catalase activity in plants co-inoculated with Bradyrhizobium and Streptomyces was 55% greater than in plants inoculated with Bradyrhizobium alone, and this value was remarkably greater than that in the other treatments. These results reinforce the beneficial effects of plant growth-promoting bacteria on the antioxidant system that detoxifies reactive oxygen species. We concluded that the combination of Bradyrhizobium and plant growth-promoting bacteria induces positive responses for coping with salt-induced oxidative stress in cowpea nodules, mainly in plants co-inoculated with Bradyrhizobium and P. graminis or co-inoculated with Bradyrhizobium and Bacillus.

Varieties of lima bean shows different growth responses when inoculated with Bacillus sp. a plant growth-promoting bacteria / Variedades de feijão-fava exibem diferentes respostas de crescimento quando inoculadas com Bacillus sp. uma bactéria promotora de crescimento em plantas

Plant growth-promoting bacteria (PGPB) comprise of soil microorganisms that cause positive effects on plant growth. The hypothesis according to which the inoculation of lima bean with PGPB Bacillus stimulates vegetative growth, which may result in a higher plant productivity, was tested. Thus, this study aimed to evaluate the effects of inoculation of two varieties of lima bean (branca and boca de moça) with Bacillus sp., UFPEDA 472 strain, based on plant growth responses. The experiment was conducted in a greenhouse using a completely randomized design. Three treatments were applied separately to each lima bean variety: the first used inoculation with Bacillus, one was submitted to nitrogen supplementation, and one was the absolute control (non-inoculated plants). The following variables were evaluated: absolute and relative growth rate, root length, stem diameter, fresh and dry mass of shoots and roots, shoot:root ratio and total chlorophyll. The results showed that lima bean displayed better growth responses when inoculated with Bacillus sp. UFPEDA 472 in relation to the treatment with nitrogen and/or non-inoculated plants. When inoculated with PGPB Bacillus, the lima bean var. branca was superior to boca de moça in terms of root length and root dry mass. The lima bean var. boca de moça inoculated with Bacillus sp. UFPEDA 472 was superior to branca in terms of absolute growth rate, stem diameter, fresh and dry mass of shoot, shoot:root ratio and total chlorophyll. In general, the lima bean var. boca de moça inoculated with Bacillus shows a better growth performance. Our results suggest that growth responses of lima bean varieties branca and boca de moça are related with a positive interaction with the PGPB Bacillus.

Bactérias promotoras de crescimento em plantas (BPCP) compreendem microrganismos do solo que causam efeitos positivos no crescimento vegetal. A hipótese de que a inoculação de feijão-fava com BPCP Bacillus estimula o crescimento vegetativo, o qual pode resultar em uma maior produtividade vegetal, foi testado. Assim, este estudo objetivou avaliar o efeito da inoculação de duas variedades de feijão-fava (branca e boca de moça) com Bacillus sp., estirpe UFPEDA 472, baseado em respostas de crescimento vegetal. O experimento foi conduzido em casa de vegetação usando um delineamento completamente ao acaso. Três tratamentos foram aplicados separadamente à cada variedade de feijão-fava: o primeiro utilizou a inoculação com Bacillus sp. UFPEDA 472, um foi submetido à suplementação com nitrogênio e um foi o controle absoluto (plantas não inoculadas). As seguintes variáveis foram avaliadas: taxa de crescimento absoluto e relativo, comprimento das raízes, diâmetro do caule, massa fresca e seca da parte aérea e raízes, relação parte aérea:raiz e clorofila total. Os resultados mostram que o feijão-fava exibiu melhores respostas de crescimento quando inoculadas com Bacillus sp. UFPEDA 472 em relação ao tratamento com nitrogênio e/ou às plantas não inoculadas. Quando inoculado com Bacillus sp. UFPEDA 472, o feijão-fava var. branca foi superior à boca de moça em termos de comprimento e massa seca das raízes. O feijão-fava var. boca de moça inoculado com Bacillus sp. UFPEDA 472 foi superior à branca na taxa de crescimento absoluto, diâmetro do caule, massa fresca e seca da parte aérea, relação

Control of gummy stem blight in watermelon through different management systems / Controle da podridão gomosa em melancia através de diferentes sistemas de manejo

Gummy stem blight, caused by Didymella bryoniae (Auersw.) Rehn, is a disease that affects the productivity of watermelon leading to losses exceeding 40%. This study aimed at evaluating the efficiency of different production systems in the control of watermelon gummy stem blight in order to establish effective methods to combat the disease. The following treatments were applied: conventional management, integrated management and organic production. Mineral fertilizer was applied to conventional and integrated management, whereas in organic production was used the cattle manure. There was application of fungicides and insecticides in commercial doses in conventional and integrated management, and the application was according to monitoring in integrated management. No fungicide or insecticide was applied to organic production. The disease severity was assessed by rating scale. The experimental design was randomized blocks. The severity of gummy stem blight increased substantially during fruit formation. Watermelon plants grown with integrated management showed lower levels of disease severity, while plants in organic production exhibited higher severity levels. We conclude that the management based on judicious monitoring in field is the best way to attain appropriate phytosanitary quality for the watermelon crop in Tocantins State, Brazil.

A podridão gomosa (Didymella bryoniae) é uma doença que afeta a produtividade da melancia levando a perdas superiores a 40%. Objetivou-se avaliar a eficiência de diferentes sistemas de produção no controle da podridão gomosa em melancia visando estabelecer métodos eficientes de combate à doença. Aplicou-se os seguintes tratamentos: manejo convencional, manejo integrado e cultivo orgânico. A adubação mineral foi aplicada em manejo convencional e no manejo integrado, enquanto que no cultivo orgânico foi utilizado o esterco bovino. Houve aplicação de fungicidas e inseticidas em doses comerciais no manejo convencional e manejo integrado, sendo que no manejo integrado a aplicação foi conforme monitoramento. A severidade da doença foi avaliada por escala de notas. O delineamento experimental foi blocos ao acaso. A severidade da podridão gomosa aumentou substancialmente na fase de formação dos frutos. Plantas de melancia cultivadas com o manejo integrado apresentaram menores níveis de severidade da doença, enquanto as plantas em cultivo orgânico exibiram maiores níveis de severidade. Conclui-se que o manejo baseado em acompanhamentos criteriosos em campo representa a melhor maneira de atingir o aspecto fitossanitário adequado para o cultivo de melancia no Estado do Tocantins, Brasil.

Escala diagramática para avaliação da severidade do crestamento gomoso do caule em melancia / Diagrammatic scale for evaluation of gummy stem blight severity in watermelon

O crestamento gomoso do caule, causado pelo fungo Didymella bryoniae, é uma doença comumente encontrada na melancia cultivada em vários países. No Brasil, são inúmeras as pesquisas relacionadas à doença, porém não há métodos padronizados de quantificação da severidade da doença em campo. Assim, foi desenvolvida uma escala diagramática com base em padrões de fotos digitalizadas de folhas de melancia infectadas com D. bryoniae. A escala desenvolvida apresentou níveis de 0; 10; 20; 45; 65 e 90% de severidade. A validação da escala foi dividida em duas partes: inicialmente, 10 avaliadores (metade com experiência e a outra metade sem experiência) estimaram a severidade da doença com base na observação inicial de 100 fotos de folhas de melancia com sintomas da doença em diferentes níveis de severidade. Em seguida, os mesmo avaliadores estimaram a severidade da doença com o auxílio da escala confeccionada a partir do programa Quant. Os dados foram analisados a partir de regressão linear e obtidos os coeficientes angular, linear e de correlação. A partir dos dados obtidos, determinou-se a acurácia e precisão das avaliações. Os coeficientes de determinação (R2) variaram entre 0,88 - 0,97 para os avaliadores experientes e de 0,55 - 0,95 para os avaliadores inexperientes. O coeficiente angular (A) médio para os avaliadores inexperientes foi de 20,42 e 8,61 sem e com o auxílio da escala diagramática, respectivamente. Os avaliadores experientes apresentaram valores de A médios de 5,30 e 1,68 sem e com o uso da escala diagramática, respectivamente. A análise dos erros absolutos indicou que o uso da escala diagramática contribuiu para minimizar as falhas na estimativa dos níveis de severidade. A escala diagramática proposta mostrou-se adequada para avaliação da severidade do crestamento gomoso do caule em melancia.

The gummy stem blight, caused by the fungus D. bryoniae, is a disease commonly found in watermelon cultivated in several countries. In Brazil, there are numerous studies related to the disease, but there are not uniform methods for quantifying of disease severity in the field. Thus, we developed a diagrammatic scale based on scanned photos of watermelon leaves infected with D. bryoniae. The scale developed showed levels of 0; 10; 20; 45; 65 and 90% of severity. The scale validation was divided into two parts: initially, 10 evaluators (half with experienced and other half without experience) estimated the disease severity based on the initial observation of 100 photos of watermelon leaves with symptoms of the disease at different severity levels. Before, the same evaluators estimated the disease severity with the support of the scale prepared from the Quant program. Data were analyzed using linear regression and were obtained angular, linear, and correlation coefficients. Based on these data, we determined the accuracy and precision of the evaluations. The correlation coefficients (R2) ranged from 0.88 - 0.97 for the experienced evaluators and from 0.55 - 0.95 for the inexperienced evaluators. The average angular coefficient (A) for inexperienced evaluators was 20.42 and 8.61 with and without the support of diagrammatic scale, respectively. Experienced evaluators showed values of average linear coefficient of 5.30 and 1.68 with and without the support of diagrammatic scale, respectively. The absolute errors analysis indicated that the use of diagrammatic scale contributed to minimize the flaws in the severity levels estimation. The diagrammatic scale proposed shown adequate for gummy stem blight severity evaluation in watermelon.

Severidade da antracnose e produtividade de sorgo granífero em resposta a doses crescentes de nitrogênio / Anthracnose severity and yield of grain sorghum in response to increasing nitrogen doses

O presente estudo objetivou avaliar a severidade da antracnose e a produtividade de diferentes genótipos de sorgo em resposta a doses crescentes de nitrogênio. Os experimentos foram conduzidos em duas safras agrícolas: safra 2009/2010 (safra I) e safra 2010/2011 (safra II). O preparo do solo na área experimental foi realizado de forma convencional. Na safra I foram utilizados quatro genótipos de sorgo BRS 310, CMSXS 0144015, CMSXS 9920045 e CMSXS 9920044, enquanto que na safra II apenas os genótipos BRS 310 e CMSXS 0144015 foram avaliados. Aos 45 dias após o plantio (DAP) foram aplicados os tratamentos que consistiram de doses de nitrogênio (67; 112; 157; e 202 kg ha-1) em adubação de cobertura. Aos 60 DAP, iniciou-se a avaliação da severidade da antracnose utilizando escala de notas. Na colheita, determinou-se a produtividade de grãos nos tratamentos. Houve variação nos níveis de severidade da antracnose e na produtividade de grãos dos genótipos de sorgo em função das doses de nitrogênio aplicadas. Os genótipos de sorgo CMSXS 9920045 e BRS 310 apresentaram menor e maior suscetibilidade à antracnose, respectivamente. No genótipo BRS 310, a doença progrediu mais rapidamente na safra I que apresentou maior umidade relativa.

The present study aimed to evaluate the severity of anthracnose and yield of different genotypes of sorghum in response to increasing levels of nitrogen. For this, experiments were conducted in two agricultural seasons: crop season 2009/2010 (crop season I) e crop season 2010/2011 (crop season II). The soil preparation in the experimental area was performed in conventional manner. In the crop season I were used four sorghum genotypes BRS 310, CMSXS 0144015, CMSXS 9920045 e CMSXS 9920044, whereas in the crop season II only the genotypes BRS 310 and CMSXS 0144015 were evaluated. At 45 days after planting (DAP) were applied the treatments which consisted of nitrogen doses (67; 112; 157; and 202 kg ha-1) in topdressing. At 60 DAP, was began the evaluation of anthracnose severity using notes scale. At the harvest it was determined the yield for each treatment based on the mass of grain. There was variation in levels of anthracnose severity and grain yield in the sorghum genotypes in response to nitrogen levels applied. The sorghum genotypes CMSXS 9920045 and BRS 310 showed smaller and higher susceptibility to anthracnose, respectively. In genotype BRS 310, the disease progressed more rapidly in the crop season I that showed major relative humidity.