Giovanni Ribeiro de Souza

Mecanismos de controle da murcha-de-esclerócio e promoção de crescimento em tomateiro mediados por rizobactérias

This study was conducted to elucidate the possible mechanisms responsible for the biocontrol of southern blight and the elements involved in tomato growth promotion by selected rhizobacteria. The rhizobacteria were characterized by carbon source utilization, fatty acid profiles, and 16S rDNA sequencing, while biocontrol mechanisms were investigated using biochemical indicators and bioassays. The rhizobacteria clustered within Agrobacterium and Kluyvera. The results indicated that iron competition and antibiosis are mechanisms that explain the biocontrol capability of southern blight by rhizobacteria. In the same way, auxin production and biological nitrogen fixation can explain growth promotion. Limitations of biological control were demonstrated because the competition capability is strain-specific for Sclerotium rolfsii, and antibiosis depends on the nutritional composition of growth media.

Ocorrência da mancha-bacteriana do feijão-caupi em Roraima e reação de cultivares

ABSTRACT Bacterial blight, caused by Xanthomonas axonopodis pv. vignicola ,is a disease that has the potential to cause damage to cowpea crops.The aims of this work were to report the occurrence of such apathogen in Roraima State, Brazil, and provide information aboutthe reaction of cowpea cultivars to that disease. The used cultivarswere BRS-Amapa, BR02-Braganca, BRS Guariba, BR17-Gurgueia, BRSMazagao, BRS Milenio, BRS Patativa, Pitiuba, BR03-Tracuateua andVita-7. The study was carried out in a greenhouse in a completelyrandomized experimental design, with four replicates, each onerepresented by two plants per pot. Incubation period and disease Halfeld-Vieira, B.A.; Nechet, K.L.; Souza, G.R. Report of cowpea bacterial blight in Roraima and reaction of cultivars. Summa Phytopathologica, v.37, n.3, p.127-130, 2011. severity were evaluated at 25 days post-inoculation. The fieldexperiment was carried out in an experimental design of randomizedblocks with four blocks, each one represented by 10 plots, and eachplot was sown with one cultivar. Inoculations were performed at 35days after sowing, at the beginning of flower bud emission. Evaluationparameters consisted of incubation period, disease severity at 12, 18,22, 27 and 29 days post-inoculation and bacterial transmissibilitythrough seeds. The cultivars BRS Mazagao, BR 17- Gurgueia and Vita-7 presented resistance reaction to bacterial blight. No bacterialtransmissibility was detected under these experimental conditions.

Reação de cultivares comerciais de tomateiro à mancha-fuliginosa

This work was performed to evaluate the reaction of commercial tomato cultivars to Pseudocercospora fuligena, the causal agent of black leaf mold of tomato, an uncommon disease of tomato fields in Brazil. Studies were conducted under protected cultivation and greenhouse conditions. Disease severity, under protected cultivation, was evaluated through the area under the disease progress curve (AUDPC). Plants in the greenhouse were evaluated for disease severity, and incubation and latent periods. Pattern of symptoms was variable according to the tomato cultivar evaluated, and disease severity ranged from 16 to 22%, in the experiment under protected cultivation. Disease severity was highest in Debora plus whereas Duradoro and San Vito were the most resistant cultivars.

Uso de pioverdina no controle da mancha bacteriana do maracujazeiro

The objective of this work was to evaluate the effect of a bacterial filtrate containing pyoverdine on the population dynamics of Xanthomonas axonopodis pv. passiflorae, and the severity of passion fruit bacterial blight. The treatments were: King’s B medium solution; King’s B medium solution with 2 μmol L-1 Fe2+ supplementation; and King’s B medium filtrate containing two concentrations of the siderophore pyoverdine produced by Pseudomonas sp. The filtrate containing pyoverdine at Abs363 = 0.231 (highest concentration) reduces the number of cells of X. axonopodis pv. passiflorae, and at Abs363 = 0.115 and Abs = 0.231 significantly reduces the severity of bacterial blight.

Influência de diferentes períodos de molhamento foliar na germinação de conídios de Pseudocercospora fuligena

Tomato leaf mold caused by Pseudocercospora fuligena is an uncommon disease in Brazil; however, it presents high damage potential to the culture. The objective of this paper was to study the influence of different leaf wetness periods on conidial germination of P. fuligena. Conidia of the pathogen were collected from infected leaflets and inoculated on the abaxial side of healthy leaflets using a brush. Treatments were represented by leaves maintained in a humid chamber for 0, 4, 8, 12, 16, 20 e 24 h periods evaluating the percentage of germinated conidia after 24 h. The experimental observations demonstrate that leaf wetness periods higher than 16 h proportionate the maximum percentage of conidial germination.