Maria Isabel Balbi-Peña

Em busca de soluções que aumentem a eficiência da água e fertilização na agricultura o uso de sistemas de irrigação por gotejamento vem se destacando. Apesar da alta eficiência, os sistemas por gotejamento possuem o problema do entupimento dos gotejadores o que compromete seu desempenho. Este problema é maior quando se utilizam fertilizantes que ainda não são difundidos na fertirrigação, como o bokashi. Este estudo teve o objetivo de verificar o desempenho de um sistema de irrigação por gotejamento com a utilização de bokashi. O sistema de irrigação por gotejamento foi instalado em condições de campo, realizando 25 ensaios para cada concentração de bokashi (5 g L-1, 10 g L-1 e 15 g L-1) e irrigação (controle). A uniformidade foi determinada pelo Coeficiente de Uniformidade de Distribuição (CUD) e monitorada pelo gráfico de controle de Shewhart. A interpolação espacial das vazões dos gotejadores foi realizada pelo método do Inverso da Distância. Concentrações de 10 e 15 g L-1 apresentaram elevados teores de sedimentos, que ocasionaram entupimentos e diminuíram a uniformidade, com 70.08% e 59.97%, respectivamente. A concentração de 5 g L-1 apesar de alguns parâmetros fisico-químicos com alto risco de entupimento, obteve uma boa uniformidade, com CUD de 88.47%. Maiores variações de vazão foram observadas ao longo das linhas laterais, com aumentos e diminuições para 10 e 15 g L-1. Devido à sua menor sensibilidade, o gráfico de controle de Shewhart não apresentou pontos fora do controle para as concentrações de 5 e 10 g L-1, e apenas alguns pontos finais para 15 g L-1, apesar da alta variabilidade do processo.

We performed genome sequencing and comparative analysis of Pantoea ananatis strains isolated from corn leaves expressing typical bacterial leaf streak (BLS) and maize white spot (MWS) symptoms to confirm bacterial identity and to understand the relationship among these strains and P. ananatis strains isolated from different plant hosts in Brazil. In pathogenicity tests, strains 4.2 and 13.3 isolated from symptomatic BLS leaves were non-pathogenic on corn. In contrast, strain B13 isolated from MWS-diseased leaf tissue caused symptoms typical of MWS. Our comparative analysis revealed that all three strains are very genetically similar. The G+C (%) content of strains 4.2 and 13.3 was 53.5%, while the B13 content was 53.7%. Average nucleotide identity (ANI) analysis showed that strains B13 and 13.3, B13 and 4.2, and 4.2 and 13.3 shared ANIs of 99.17%, 99.15% and 99.99%, respectively. Strains 13.3, B13, and 4.2 shared ~99% ANI with P. ananatis type strain LMG 2665. To the best of our knowledge, these are the first genome sequences of P. ananatis strains isolated from corn in Brazil.

Target spot, caused by Corynespora cassiicola, is a major soybean disease that may lead to early defoliation and yield loss. This study aimed to develop and validate a diagrammatic scale for assessing target spot on soybean cotyledons; compare seed and spray inoculation methods in V4 stage plants under greenhouse conditions; and correlate the severity of artificial inoculations with natural field conditions. Cotyledons with varying severity levels were photographed and analyzed using the Assess® software. The resulting scale included five severity levels based on the Weber-Fechner law: 0.3, 2.9, 20.8, 70.0, and 95.4 %. The use of this scale improved the precision and accuracy, even for inexperienced evaluators. Thirty-five genotypes (26 lines and nine cultivars) were tested under controlled conditions and later in field trials carried out in Lucas do Rio Verde and Campo Novo do Parecis (Mato Grosso state, Brazil). Both inoculation methods differentiated the genotype responses, with seed inoculation showing a higher repeatability. The trial in Lucas do Rio Verde was more informative because of the greater disease severity and showed a positive correlation with the greenhouse results.

The main objective of this study was to investigate the antimicrobial activity of three putative antagonist bacterial strains of Bacillus spp. against Xanthomonas vasicola pv. vasculorum (Xvv) and their potential to control bacterial leaf streak (BLS) of corn. Additionally, the study included investigations on the genome of one of these antagonist bacteria, such as genome sequencing and mining of genes involved in biofilm formation, swarming motility, and synthesis of secondary metabolites. The growth of Xvv was inhibited by both cell suspensions and cell-free supernatants of the bacterial strains LAFUEL 01, LAFUEL 02, and LAFUEL 03 in agar diffusion tests. All three antagonist strains significantly reduced the severity of BLS in the 3rd and 4th leaves of corn plants that were artificially inoculated at the V3 growth stage under greenhouse conditions. The 16S rRNA sequencing confirmed that the antagonistic bacterial strains belong to the genus Bacillus, with LAFUEL 03 having approximately 97% similarity to B. velezensis. B. velezensis LAFUEL 03 harbors genes related to the biosynthesis of secondary metabolites, biofilm formation/regulation, and swarming motility that enhances its potential for controlling BLS in corn and suggests a promising candidate for the development of a commercial biocontrol agent.

Bacterial leaf streak caused by Xanthomonas vasicola pv. vasculorum (Xvv) is an emerging disease in several corn-producing regions around the world. In Brazil, there is a lack of information on the survival of this bacterium in soil and crop residues. Thus, the objective of this study was to determine the survival of Xvv in soil and also in infected corn crop residues under the humid subtropical climate of southern Brazil. The survival of Xvv in soil was initially investigated in sandy and clayey soils maintained at 20, 25 and 30 °C under controlled conditions. The survival of the bacterium under field conditions was studied in artificially infested clayey soil. The survival of Xvv in corn crop residues was investigated in infected residues maintained on the soil surface or buried in the soil at 20 cm deep. Under controlled conditions, regardless of the type of soil, the bacterium survived longer at 20 °C than at higher temperatures. The bacterium survived for 40 days in clayey soil kept at 20 °C and four days in sandy soil maintained at 30 °C. Under field conditions, the survival of Xvv in the soil was only for 48 h and in infected corn crop residues for up to 15 days in the samples maintained on the soil surface. In samples of infected corn residues buried in the soil, the bacterium was only detected at the time the experiment was set up. In general, the results obtained in this study revealed that Xvv survives for a short period of time in soil and in infected corn crop residues under humid subtropical conditions. Therefore, soil and corn residues may not be highly important sources of primary inoculum for the development of bacterial leaf streak on corn crops under these conditions.

O feijão tem uma grande importância alimentar e socioeconômica para a população mundial. No entanto, a produção de feijão sofre reduções por causa de doenças causadas por patógenos de solo. O uso intensivo de produtos químicos para o controle destes tem várias desvantagens, incluindo danos à saúde humana e ao meio ambiente além de provocar desequilíbrios na dinâmica de doenças e pragas da cultura. Alguns produtos comerciais, registrados como biofertilizantes ou aditivos de compostagem têm apresentado controle de fitopatógenos. Este trabalho teve como objetivo a avaliação do desempenho de biofertilizantes e aditivo de compostagem e suas misturas no controle da podridão radicular seca (causada por Fusarium solani f. sp. phaseoli) e da murcha de Fusarium (causada por Fusarium oxysporum f. sp. phaseoli) em plantas de feijoeiro em casa-de-vegetação. Adicionalmente, este estudo investigou o efeito desses produtos e suas misturas no desenvolvimento do feijoeiro. O delineamento experimental foi inteiramente casualizado com seis repetições. Foram testados os produtos Soil-Plex Trust®, Soil-Plex Ready®, Soil-Plex Active® e Nem-Out® e suas misturas, fungicida químico Captan® (controle positivo), água (controle negativo) e um controle constituído por plantas não inoculadas com o patógeno. O produto Soil-Plex Trust® reduziu a severidade da podridão radicular seca. Os produtos Soil-Plex Trust®, Soil-Plex Active® e a mistura (Soil-Plex Ready® + Soil-Plex Active®) promoveram um peso seco da raiz igual ao de plantas sem inocular. Considerando ambos os métodos de inoculação, a aplicação de Soil-Plex Trust® sozinho no sulco de plantio reduziu a severidade da murcha de Fusarium em feijoeiro. Plantas tratadas com Soil-Plex Trust® + Soil-Plex Active® e Soil-Plex Ready® + Soil-Plex Active® e inoculadas com F. oxysporum f. sp. phaseoli pelo método do disco micelial, também apresentaram menor severidade de murcha de Fusarium. As misturas Soil-Plex Trust® + Soil-Plex Active®, Soil-Plex Ready® + Soil-Plex Active®e Nem-Out® Soil-Plex Active®, determinaram um comprimento de raiz igual ao de plantas sem inóculo. Os resultados indicam que biofertilizantes e aditivos de compostagem à base de Bacillus e Trichoderma podem ser utilizados na estratégia de controle de doenças causadas por Fusarium spp. e ainda contrarrestar as reduções de crescimento do feijoeiro ocasionadas por esses fungos.

O antagonismo do Bacillus velezensis LABIM40 (cepa CMRP 4489) foi avaliado in vitro contra Alternaria linariae, Botryotinia squamosa, Colletotrichum lindemuthianum, Gibberella zeae e Rhizoctonia solani. Com o objetivo de avaliar o efeito de diferentes formulações de LABIM40 no crescimento de mudas de tomateiro e no biocontrole do tombamento causado por R. solani, foi conduzido um experimento com sementes tratadas em condições de câmara de crescimento. Os tratamentos foram suspensão de células de LABIM40, LABIM40 SLC, SLC 10 vezes concentrado (10xSLC), produtos comerciais à base de Bacillus amyloliquefaciens (PC_1) e Bacillus subtilis (PC_2) e água. Os efeitos do produto foram avaliados em mudas de tomate cultivadas em substrato estéril e em substrato inoculado com R. solani. No teste de cultura dupla, B. velezensis LABIM40 inibiu em 46,6, 67,4, 64,7, 49,0 e 54,4% o crescimento micelial desses fungos fitopatogênicos, respectivamente. A concentração inibitória mínima para cada fungo foi determinada por diferentes concentrações de sobrenadante livre de células (SLC) em meio de batata dextrose ágar (PDA), seguido de análise de regressão da inibição do crescimento micelial. Com exceção de A. linariae, em todos os casos o modelo com melhor ajuste foi o logarítmico. A sobrevivência de mudas de tomate de sementes tratadas com 10xSLC em substrato inoculado foi 57% maior do que o tratamento controle. Não foi observada promoção de crescimento em plantas de tomate oriundas de sementes tratadas com células de LABIM40 ou metabólitos de seu SLC. Coletivamente, esses resultados destacam a atividade antagonista de B. velezensis LABIM40 contra A. linariae, B. squamosa, C. lindemuthianum, G. zeae e R. solani verificada por cultura dupla e testes de difusão de sobrenadante livre de células e seu potencial como agente de biocontrole do tombamento do tomateiro.

Bacterial pustule caused by Xanthomonas citri pv. glycines (syn. X. axonopodis pv. glycines) is an important bacterial disease for soybean production worldwide. Currently, the planting of resistant soybean cultivars is the main measure for control of the disease. Therefore, the objectives of this study were to determine the aggressiveness of different X. citri pv. glycines isolates and to establish a new protocol to evaluate the reaction of soybean cultivars to bacterial pustule under greenhouse conditions. The molecular analysis based on the entire 16S rRNA gene sequence revealed that the isolates GDM 01, GDM 02, 333 and 87-2 belong to the X. citri pv. glycines pathovar with 100% identity with the pathotype strain K29 of this bacterium. Differences in aggressiveness were observed among the X. citri pv. glycines isolates. There were differences in the reaction of the soybean cultivars to bacterial pustule, depending on the inoculation method. The isolates 333, GDM 01 and GDM 02 were the most aggressive, while 87-2 and GDM 03 were the least aggressive ones. The best conditions for inoculation of the soybean plants were in the V3 vegetative growth stage with the inoculum concentration of 10⁸ CFU mL⁻¹, and moist chamber for 24 h before and after inoculation. Spraying without injury was the quickest and most practical inoculation method to screen soybean genotypes for resistance to bacterial pustule in breeding programs. Further, this method of inoculation closely simulates the natural bacterial infection under field conditions and produces typical symptoms of the disease. The standard brush inoculation method overestimated disease severity, so we do not recommend this method for the evaluation of bacterial pustule resistance in soybean breeding programs.

Bacterial leaf streak (BLS) of maize (Zea mays), caused by the bacterium Xanthomonas vasicola pv. vasculorum (Xvv), was first reported in Brazil in 2018. In this study, we evaluated 52 species of cultivated plants, cover crops, forage, and grasses that are used in succession or crop rotation with maize, and weeds with natural occurrence in maize-producing regions, to determine their potentials as alternative hosts for Xvv. We investigated (i) the pathogenicity of Xvv based on symptom development, (ii) epiphytic colonization of the bacterium in asymptomatic plants, and (iii) bacterial colonization in plant tissues using scanning electron microscopy (SEM) in symptomatic and asymptomatic species. Ten species, all belonging to the Poaceae family, presented symptoms after Xvv infection, including Avena sativa (cvs. IPR Afrodite and IPR Esmeralda), A. strigosa (cv. IPR 161), Hordeum vulgare (cv. BRS Cauê), Oryza sativa (cv. IPR 117), Brachiaria brizantha (Brizantha and cv. Marandu), Digitaria horizontalis, D. insularis, Echinochloa colonum, Eleusine indica, and Sorghum arundinaceum. Furthermore, epiphytic colonization by Xvv was observed in 23 asymptomatic species. Scanning micrographs revealed that Xvv cells and their aggregates were distributed throughout the leaf surface. In addition, bacterial colonization in the intercellular tissues of the substomatal chambers of white oat, black oat, and maize was observed across the tissue fractures. Despite showing typical symptoms of Xvv infection, SEM examination revealed evidence of Xvv colonization only on the leaf surface of rice. In asymptomatic species, such as rye, sorghum, and millet, a low number of bacterial cells were found on the leaf surface. However, no evidence of internal tissue colonization was observed in millet fractures, suggesting that Xvv survives only epiphytically in this species.

Bacterial leaf streak caused by Xanthomonas vasicola pv. vasculorum is an emerging disease for corn production around the world. However, information on management of this disease is still limited. This study aimed to determine the in vitro sensibility of X. vasicola pv. vasculorum to different chemicals and to evaluate the control of bacterial leaf streak on corn under greenhouse conditions. In vitro tests were carried out with kasugamycin, copper sulfate, copper oxychloride, copper hydroxide, cuprous oxide, bioactive copper, mancozeb, chlorothalonil, methyl thiophanate, and tebuconazole at the dosages of 1, 5, 10, 20, 50, 100, 200, and 400 μg mL⁻¹. Four strains of X. vasicola pv. vasculorum were included in the study. The minimal inhibitory concentration for kasugamycin ranged from 50 to 200 μg mL^–1, whereas to the inorganic copper compounds varied from 5 to 50 μg mL^–1 and to the bioactive copper was 100 μg mL^–1. Further, mancozeb and tebuconazole inhibited the bacterial growth at the dosage ranging from 5 to 20 μg mL^–1 and 50 to 400 μg mL^–1, respectively, depending on the X. vasicola pv. vasculorum strain. Chlorothalonil and methyl thiophanate did not inhibit the growth of the bacterium at any tested concentration. The control of bacterial leaf streak under greenhouse conditions was investigated on corn plants of the cultivar IPR 164 at the V3 phenological vegetative stage, sprayed with kasugamycin (3 mL L^–1), copper oxychloride (1.5 mL L^–1), bioactive copper (1 mL L^–1), mancozeb (2 g L^–1), tebuconazole (1 mL L^–1), and chlorothalonil (2 mL L^–1). The corn plants were inoculated with a 10⁸ CFU mL^–1 suspension of the RL1 strain of X. vasicola pv. vasculorum. Only copper oxychloride significantly reduced disease severity. However, this copper compound caused phytotoxicity to the corn plants at the tested concentration.