Vanessa de Fátima Jerba

Relação entre a estrutura foliar de feijoeiro e a pré-infecção por Glomerella cingulata f.sp. phaseoli

The objectives of this work were to measure the secondary vein area and to quantify the trichomes of leaf surface in bean cultivar susceptible (Carioca), medium resistant (Perola) and resistant (IAPAR-81) to anthracnose, and to observe relationships between leaf blade characteristics with the preinfectional stages. In order to measure the secondary vein area, sample leaf pieces were fixed in FAA 50 and conserved in 70% alcohol. These leaf samples were infiltrated in glycol metacrylate resin, cut transversally and stained with toluidine blue. The trichomes were quantified in epidermical impressions in projection microscopy. The material for preinfection analysis was fixed in 2.5% glutaraldehyde and processed to study the scanning electron microscopy. The resistant cultivar showed minor secondary vein area and high pilosity than the cultivar medium resistant and susceptible. In the resistant cultivar, due to minor vein area and high pilosity, the pathogen stayed on the vein and involved on the trichomes. In susceptible cultivar, with high vein and minor pilosity, necrosis and fungal structure on the leaf surface were observed. The results show a relation between the minor vein and high leaf trichomes quantity with the resistance to the anthracnose in pathogen preinfection stages.

Nematofauna fitopatogênica de sementes comerciais de forrageiras tropicais

The objective of this work was to identify and quantify the phytopathogenic nematofauna of forage seeds destined for internal and external markets. Seeds of Brachiaria brizantha (cvs. Marandu and Xaraes), B. decumbens cv. Basilisk, Panicum maximum (cvs. Massai, Mombaca and Tanzania), and Stylosanthes capitata and S. macrocephala, components of cv. Estilosantes Campo Grande, were examined. The extractions were made by centrifugal flotation in solution of sucrose with kaolin. Aphelenchoides and Ditylenchus genera were detected in forage grasses. The highest number of Aphelenchoides spp. specimens was observed in seeds of cv. Marandu, followed by seeds of cvs. Xaraes, Basilisk, and Tanzania. Regarding Ditylenchus spp. population density, higher values were detected in seeds of cvs. Marandu, Xaraes, and Basilisk. The results suggest that two or more species of Aphelenchoides and Ditylenchus are associated to forage grass seeds destined for Brazilian market. Phytopathogenic nematodes are not detected in Estilosantes Campo Grande seeds, neither in seeds of cvs. Marandu, Mombaca and Tanzania destined for exportation.

Atividade pectinolítica de Colletotrichum gloeosporioides e a relação com a agressividade ao Stylosanthes spp

Pectinolytic activity of 40 isolates of Colletotrichum gloeosporioides obtained from Stylosanthes spp.lesions, in distinct producing regions, was estimated through the enzymatic diffusion in pectin-medium free of glucose, and measured by pectin degradation. All isolates showed pectinolytic activity, and were divided in five groups. Moderate production of pectic enzymes was evidenced in the majority of the isolates. In general, isolates from Camapua-MS presented low genetic diversity for the production of pectinases. Taking into account the activity of pectinases, isolates of the pathogen were selected and inoculated in S. capitata (GC1081, GC1084, GC1086 and GC1094), S. scabra (GC1496) and S. macrocephala (GC1511). Thus, the enzyme influence on aggressiveness to the host was evaluated. Initially, aggressiveness test was installed with the isolates CG656, CG657, CG687, CG706 and CG707. Differences in aggressiveness were observed only when the isolates were inoculated in S. scabra. The isolates CG657, CG706 and CG707 were the most aggressive, and CG656 was the least aggressive. Another aggressiveness test was established to evaluate the isolates CG768, CG769, CG772, CG775, CG779 and CG781. These isolates showed differences in their aggressiveness when inoculated in S. capitata (GC1081 and GC1094) and S. macrocephala (GC1511). In general, CG768 exhibited the lowest while, CG772, CG775 and CG781 the highest aggressiveness. In both aggressiveness tests, there were no evidences for a direct correlation of anthracnose increase in severity with the of the pectinolytic activity. For the conditions evaluated, the pectic enzymes did not influence the aggressiveness of C. gloeosporioides to the stylo.

Quimio e termoterapia em sementes e aplicação de fungicidas em Brachiaria brizantha como estratégias no manejo do carvão

This work investigated the potentials of the thermal and chemical treatments in seeds of Brachiaria brizantha cv. Piata, which have been described as efficient strategies to overcome the physical dormancy of seeds, in the reduction of smut (Ustilago operta). Samples of seeds were immersed in sulfuric acid for 0 to 10 min, or in hot water (27 to 60 oC) for 5 or 10 min. The effects of the treatments in the number of remaining teliospores of U. operta and in the germination of treated seed have been evaluated. A decrease of inoculum was observed as the time of chemical scarification of seeds was increased. The reduction on the number of teliospores was superior with 10 min of chemotherapy. In general, the exposition to H2SO4 did not result in a decrease of the germinative power of the seeds. The results of the thermotherapy were not as evident as those observed for the chemotherapy. Reductions on the number of teliospores or on the overcoming of the physical dormancy were less apparent, maybe, because the seeds were not immersed in hot water during enough time. In parallel, the efficiency of the application of fungicides on the aerial part of the plants for the control of the smut incidence was verified. The fungicides tested were as follow: 1 - methylic tiofanato + chlorothalonil; 2 - mancozeb; 3 - tebuconazole; 4 - triadimenol; 5 - azoxystrobin + cyproconazole; 6 - pyraclostrobin + epoxyconazole; 7 - trifloxystrobin + cyproconazole; 8 - carboxin + thiram; 9 - methylic tiofanato + flutriafol; 10 - carbendazin, and 11 - difenoconazole. Although the smut incidence observed in the experimental area was low (maximum of 15%), a differentiation among the fungicides was possible. The tebuconazole, pyraclostrobin + epoxyconazole and trifloxystrobin + cyproconazole were the most promising fungicides.

Puccinia levis var. panici-sanguinalis em Brachiaria brizantha cv. Xaraés

que nao apresentou sintomas de ferrugem. Aposanos de estudos, perante o bom desempenho desse genotipo, o mesmo foilancado comercialmente em 2002 como cultivar Xaraes.Recentemente, observaram-se manchas cloroticas e necroticas,pustulas sub-epidermicas irrompentes de coloracao castanho-escura eseca prematura das folhas de ‘Xaraes’, tipicos sintomas/sinais deferrugem (Figura 1A-C). Esporos foram coletados das pustulas eobservados ao microscopio de luz para a identificacao do agenteetiologico. Constatou-se a presenca de teliosporos bicelulares compedicelos longos inseridos na parede divisoria das celulas oulateralmente em uma destas (Figuras 1E-F), e urediniosporosunicelulares marrons escuros (Figura 1D). Em geral, os teliosporosapresentaram comprimento superior a 40 µm e 3 µm de espessura deparede lateral. Foram observados urediniosporos com 3 porosgerminativos. Baseado nessas caracteristicas morfologicas, a ferrugemfoi identificada como