Rosa de Lima Ramos Mariano

Plant Growth Promoting Rhizobacteria: Fundamentals and Applications

Plant growth promoting rhizobacteria (PGPR) have gained worldwide importance and acceptance for agricultural benefits. This is due to the emerging demand for dependence diminishing of synthetic chemical products, to the growing necessity of sustainable agriculture within a holistic vision of development and to focalize environmental protection. Scientific researches involve multidisciplinary approaches to understand adaptation of PGPR, effects on plant physiology and growth, induced systemic resistance, biocontrol of plant pathogens, biofertilization, and potential green alternative for plant productivity, viability of coinoculating, plant microorganism interactions, and mechanisms of root colonization. By virtue of their rapid rhizosphere colonization and stimulation of plant growth, there is currently considerable interest in exploiting these rhizosphere bacteria to improve crop production. The main groups of PGPR can be found along with the phyla Cyanobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Therefore, the examples coming up next are related to these microorganisms. Although taxonomic affiliation of validated genera containing PGPR strains described in literature is vast, phenotypic and genotypic approaches are now available to characterize these different rhizobacteria. The progress to date in using PGPR in a variety of applications is summarized and discussed here.

Antimicrobial action of the essential oil of Lippia gracilis Schauer

Avaliou-se a atividade antimicrobiana do oleo essencial (OE) de Lippia gracilis Schauer sobre fungos contaminantes de laboratorios de cultura de tecidos vegetais e bacterias endofiticas de heliconias. Discos de micelio dos fungos Geotrichum candidum; Trichoderma viride; Torula herbarum; Paecillomyces sp.; Aspergillus nidulans; Fusicoccum sp.; A. flavus; P. aeruginens; Curvularia lunata e A. niger, foram inoculados em meio BDA com oleo (0; 420; 440; 460; 480 e 500 µL L-1). O percentual de inibicao em 420 µL L-1 foi de 100% para todos os fungos exceto paraC. lunata and A. niger, o qual foi de 95.58% and 89.40% respectivamente. Em outro experimento, suspensao das especies Salmonela choleraceuis-diarizonae, Enterobacter asburiae, Bacillus thuringiensis, B. pumilus, Klebsiella pneumoniae, E. hormaechei, Bacillus pumilus, B. cereus, B. pumilus foi individualmente adicionada ao meio NYDA, que foi vertido em placas de Petri e, apos solidificado, perfurado e preenchido com agua ou oleo (420 µL L-1). Avaliou-se o diâmetro do halo de inibicao. Avaliou-se tambem, a inibicao em meio liquido. K. pneumoniae foi a especie bacteriana menos sensivel e E. hormaechei foi a mais sensivel.

Antagonism of Bacillus spp. against Xanthomonas campestris pv. campestris

The antagonism of eight Bacillus isolates was investigated against nine strains of Xanthomonas campestris pv. campestris (causal agent of crucifers black rot) to assess the role of lipopeptides in this process. Antimicrobial and hemolytic (surfactant) activity tests were performed in vitro using agar diffusion methods. Antibiosis and hemolysis were positive for four Bacillus isolates against all X. campestris pv. campestris strains. The correlation observed between antimicrobial and hemolytic activities indicated that lipopeptides were involved in the antibiosis mechanism of the studied antagonists. Fermentation studies were carried out with the isolates that showed highest antimicrobial and hemolytic activities, to follow up growth and production of bioactive and surfactant compounds. Production of bioactive and surfactant compounds was observed during the late growth phase of the Bacillus isolates.

Antagonism of Trichoderma species on Cladosporium herbarum and their enzimatic characterization

The verrucose caused by Cladosporium herbarum reduces production and quality of Passion fruit (Passiflora edulis Sims.), a largely consumed tropical fruit. This work aimed to investigate the antagonism of Trichoderma species (T. polysporum, T. koningii, T. viride and T. harzianum) against Cladosporium herbarum, and to study the production of extracellular hydrolytic enzymes by the pathogen and the antagonists. The results showed considerable antagonistic potential for the biocontrol of C. herbarum isolates by all Trichoderma species, except T. koningii. The most distinguished effect was observed for T. polysporum. In relation to the pattern of esterase obtained by electrophoresis in poliacrylamyde gel, the major activity presented by the isolates was observed after five days of incubation. The C. herbarum isolates produced extracellular enzymes, lipase, pectinase, cellulase, and protease, all possibly related to the infection process. Amylase excretion, not known to be associated with phytopathogens, was detected in Trichoderma species, but not in C. herbarum. In addition to amylase, all Trichoderma species tested produced also extracellular cellulase and pectinase, except T. koningii in relation to the latter enzyme. The demonstration of various esterase isoenzymes in zymograms of the Trichoderma species and C. herbarum isolates was markedly improved by washing the mycelia with detergents or EDTA. This fact suggested that a major fraction of extracelular enzymes may remain attached to outside fungal cell wall after being excreted.

Epiphytic bacteria antagonistic to Curvularia leaf spot of yam

Curvularia eragrostidis yam leaf spot is a serious concern among the northeast Brazilian yam growing areas. In order to study its biocontrol, bacterial isolates from the yam phylloplane were tested against the pathogen. They were evaluated with respect to the following parameters: (1) inhibition of C. eragrostidis mycelial growth by using paired culture and cellophane membrane methods, (2) inhibition of conidium germination by using a paired suspension test, (3) reduction of disease severity and, (4) persistence of antagonistic action, on plants under greenhouse conditions. From a total of 162 bacterial isolates, 39 showed antagonism to the pathogen in paired culture. The bacteria produced extracellular, nonvolatile, and diffusible metabolites in the membrane cellophane test. Seventeen isolates resulted in more than 75% inhibition of C. eragrostidis mycelial growth. Among them, IF-26 showed the greatest antagonism. The isolates IF-82, IF-88, and IF-109 inhibited pathogen conidial germination, with average inhibition levels of 99.2, 98.2 and 96.2%, respectively. Under greenhouse conditions the antagonists were applied at three different time intervals relative to C. eragrostidis inoculation: 3 days before, at the same time, and 3 days after. IF-82 and IF-88 applied at the same time as pathogen inoculation both reduced disease severity 75%. IF-82 showed the best persistence of antagonistic action, with an average of 96.3%. IF-82, identified as Bacillus subtilis, was the best biocontrol agent for the yam leaf spot disease in this study.

Greenhouse screening ofTrichoderma isolates for control ofCurvularia leaf spot of yam

TenTrichoderma isolates were studied under greenhouse conditions as potential agents for biocontrol of yam leaf spot, caused byCurvularia eragrostidis. TheTrichoderma isolates demonstrated high efficiency of disease control. Application of the antagonists on the same day asC. eragrostidis inoculation showed the best results. One isolate achieved 75 percent disease severity reduction. The survival of theTrichoderma isolates decreased after its application on the phylloplane with values of 57 and 41 percent at the 49th day, in the absence and presence of the phytopathogen respectively. The antagonism persisted well againstC. eragrostidis, the TN1 isolate praises 89 percent.

Management of melon bacterial blotch by plant beneficial bacteria

Plant beneficial bacteria (PBB) have shown potential for disease control and are particularly important in the management of bacterial diseases, which are poorly controlled by conventional methods. In melon, bacterial fruit blotch caused by Acidovorax citrulli is a seedborne disease that is particularly destructive under certain conditions. PBB strains were screened for their ability to protect seeds and leaves from bacterial fruit blotch, and their antibiosis activity and plant colonization were studied. When Bacillus sp. RAB9 was applied to infected seeds, it reduced the area under the disease progress curve (AUDPC) by 47% and increased the incubation period (the time between inoculation and the first visible symptoms) by 35%. Three of the selected strains (JM339, MEN2 and PEP91) displayed antibiosis against A. citrulli. The RAB9Rif-Nal mutant colonized seeds epiphytically and roots and stems endophytically. Paenibacillus lentimorbus MEN2 sprayed on melon seedlings protected leaves, and when challenged with A. citrulli, it reduced the AUDPC (by 88%), disease index (by 81%) and incidence (by 77%). Given that the production of both melon seedlings and commercially grown greenhouse melons is increasing, biocontrol strategies may well be integrated into bacterial blotch management programs.

Moko Disease-Causing Strains of Ralstonia solanacearum from Brazil Extend Known Diversity in Paraphyletic Phylotype II

The epidemic situation of Moko disease-causing strains in Latin America and Brazil is unclear. Thirty-seven Ralstonia solanacearum strains from Brazil that cause the Moko disease on banana and heliconia plants were sampled and phylogenetically typed using the endoglucanase (egl) and DNA repair (mutS) genes according to the phylotype and sequevar classification. All of the strains belonged to phylotype II and a portion of the strains was typed as the Moko disease-related sequevars IIA-6 and IIA-24. Nevertheless, two unsuspected sequevars also harbored the Moko disease-causing strains IIA-41 and IIB-25, and a new sequevar was described and named IIA-53. All of the strains were pathogenic to banana and some of the strains of sequevars IIA-6, IIA-24, and IIA-41 were also pathogenic to tomato. The Moko disease-causing strains from sequevar IIB-25 were pathogenic to potato but not to tomato. These results highlight the high diversity of strains of Moko in Brazil, reinforce the efficiency of the egl gene to reveal relationships among these strains, and contribute to a better understanding of the diversity of paraphyletic Moko disease-causing strains of the R. solanacearum species complex, where the following seven distinct genetic clusters have been described: IIA-6, IIA-24, IIA-41, IIA-53, IIB-3, IIB-4, and IIB-25.

Bacterização de sementes e desenvolvimento de mudas de pepino

Epiphytic and endophytic bacteria were isolated from healthy cucumber plants, collected in several counties of Pernambuco State, Brazil, and evaluated for seedling growth promotion under greenhouse conditions. Three bioassays were performed. In the first, 93 strains were tested; in the second, 32, and, in the third, eight from cucumber plus 10 bacterial epiphytic strains from other crops were used. The cucumber seeds were bacterized by immersion in the bacterial suspension adjusted to A580 = 0.7, sown in polystyrene trays filled with organic substrate and analyzed ten days after sowing in relation to shoot (MSPA), root (MSR), and total (MST) dry matter. In the third bioassay the epiphytes PEP52, PEP8, PEP82, PEP91, and C22 were selected because they significantly (P=0.05) elevated MSR and MST in relation to the control reaching higher values than 70 and 40%, respectively. After compatibility tests the five isolates applied separately and in mixtures efficiently increased the index of MSPA, MSR, and MST in cucumber seedlings, without differing among them. It is worth noticing that PEP81 (Bacillus amyloliquefaciens) and PEP91 (Enterobacter cloacae) increased 55.5 and 34.5% (MSPA), 42.9 and 37.2% (MSR), and 41.6 and 34.0% (MST), respectively. The production of indolacetic acid, hydrogen cyanide, phosphate solubilization and changes in foliar levels of N, P, K, Ca, and Mg were evaluated as putative mechanisms of action for theses isolates, but they showed negative results. Seed bacterization with B. amyloliquefaciens PEP81 and E. cloacae PEP91 could improve quality of cucumber seedlings.

Isolamento, seleção de bactérias e efeito de Bacillus spp. na produção de mudas orgânicas de alface

ABSTRACT Isolation, selection of bacteria, and effect of Bacillus spp. inthe production of organic lettuce seedlings Epiphytic and endophytic bacterial strains isolated from healthylettuce plants were evaluated for growth promotion of seedlings andplants respectively under greenhouse and field conditions of organicproduction of lettuce, in Brazil. The cultivar Veronica was utilized inthe greenhouse experiments and cvs. Veronica and Verdinha wereevaluated in the field. The strains were applied by simultaneousbacterization of seed and substrate. In the field the most efficient strainsC25 ( Bacillus thuringiensis subvar. kenyae ) and C116 ( Bacilluspumilus ) were utilized separated and in mixture after the compatibilityassay. In greenhouse root fresh weight (MFR), shoot fresh weight(MFPA) and total fresh weight (MFT) were evaluated 21 days afterbacterization. In field the total fresh weight of commercial plants wasdetermined 21 and 28 days after transplant, respectively for cvs.Verdinha and Veronica. The mechanisms of BPCP studied wereproduction of indolacetic acid, cyanidric acid, phosphate solubilizationand alterations of N, P, K, Ca and Mg foliar levels. In the greenhouse,seedlings treated with C116 showed significant increase in relation tocontrols for MFR, MFPA and MFT as well as those treated with C25for MFR and MFT. In the field cvs. Verdinha and Veronica treatedwith C25, C116 or mixture did not significantly differ from control.None of the analyzed mechanisms were positive but strain C25significantly increased the level of foliar N.