Resumo em Inglês:

The temporal progress of anthracnose (Colletotrichum gloeosporioides) epidemics was studied in mango (Mangifera indica) orchards treated with fungicides from different chemical groups, mode of action, and application sequences in two regions of contrasting climates (sub-humid and dry tropics) in Guerrero, Mexico. Full flowering, initial setting, and 8-15mm Ø fruits were identified as critical stages for infection. Epidemics started 20-26 days after swollen buds, and maximum severity was attained at 40-42 days after the first symptoms were detected. The Weibull model described (r²>0.89) anthracnose epidemics in both floral and vegetative flushes. Active ingredients of different fungicide groups, mode of action, and residuality such as myclobutanil, azoxystrobin, cyprodinil+fludioxonil, quinoxyfen, and chlorotalonil + sulfur led to significantly low values (LSD<0.05%) in the Yf, AUDPC and b-1 parameters. The best strategy was to initiate a preventive treatment with a systemic ingredient, independently of its chemical group. Severity of the disease in floral (Fl) and vegetative flushing (Veg) in the sub-humid tropic was related with temperature >30ºC (rFl=0.79-0.86; rVeg=0.80-0.95) and relative humidity > 90% (rFl=0.66-0.86; rVeg=0.67-0.94). In both regions, conidial sporulation was related to temperature >30ºC (r=0.72-0.74), relative humidity <60% (r=0.66), severity (rFl=0.62-0.98; rVeg=0.75-0.97) and dew point <25ºC (r=0.68-0.69).

Resumo em Inglês:

Field trials were conducted in 2008/2009 and 2009/2010 growing seasons at Giza Agricultural Research Station to evaluate powdery mildew (PM) severity on nine flax cultivars. Tested cultivars could be classified into five distinct groups, i.e., highly susceptible (Corland and C.I. 2008), susceptible (Giza 7 and Marshall), moderately susceptible (Cass), moderately resistant (Dakota, Koto and Wilden) and resistant (Ottowa 770B). They showed considerable variation in PM severity ranging from 8.1 on Ottowa 770B to 97.0% infected leaves/plant on Cortland. Total soluble proteins, total phenols, peroxidase, polyphenoloxidase, ascorbic acid, tocopherol and malondialdehyde were determined in infected leaves of the tested cultivars. Pearson's correlation coefficient was calculated to measure the degree of association between PM severity and each biochemical component. All components showed significant (P<0.05) or highly significant (P<0.01) negative correlation with PM severity except MDA, which showed positive correlation (P<0.01). The results of the present study suggest that phenols and MDA in infected leaves could be used to assist the screening of resistant plants at early stages of powdery mildew development.

Resumo em Inglês:

Fusarium root rot (FRR) is a distributed disease of common beans in Brazil. Our main aim was to verify if there are genotypes, mainly advanced lines from the common bean breeding program with levels of resistance to FRR similar to those of the line A-300. We also compared three developmental stages for FRR assessment. Genotypes of six classes were evaluated in greenhouse and field experiments. In greenhouse, substrate was infested with chlamydospores. In field, genotypes were screened in area infested with Fusarium solani f. sp. phaseoli. Plants were rated for disease at V3, R5 and R7 stages. Correlation among area under the disease progress curve (AUDPC) in greenhouse and in the field experiments was significant. Genotypes were ranked into four groups based on AUDPC. Sixteen advanced lines were as resistant to FRR as A-300. Correlation between the disease rating at R5 stages and AUDPC was higher than those among AUDPC and either disease rating at V3 or R7 in all experiments. Our results indicate that there are advanced lines with levels of FRR resistance similar to those of A-300 and that the FRR assessment at the R5 stage is more appropriated than at either V3 or R7.

Resumo em Inglês:

The objective of this study was to characterize isolates of biovar 2 of Ralstonia solanacearum pathogenic to eucalyptus "urograndis" hybrid by means of biochemical tests, as well as evaluation of host range and identification by PCR with primers for species, biovar and phylotype. Carbohydrate utilization assays revealed that the eucalyptus isolates belong to phenotype Tropical of biovar 2 (2T). From artificial inoculations it was possible to reproduce symptoms or recover the bacterium from: eucalyptus, potato, tomato, eggplant, datura, geranium, turnip, mustard, nasturtium, beetroot, sunflower, bean, French marigold, horseradish tree, and cashew. The PCR assays confirmed that the isolates belong to biovar 2, phylotype II of the bacterium. The confirmation of new biovar naturally infecting eucalyptus indicates that R. solanacearum easily adapts to new hosts.

Resumo em Inglês:

This study aimed to investigate the effect of silicon (Si) on the reduction of brown spot severity (BSS), caused by Bipolaris oryzae, and grain discoloration in several rice genotypes. An experiment was conducted in a greenhouse where eight genotypes were evaluated for their response to Si rates and decrease on BSS. The relationship between Si rates and BSS was linear negative. Additionally, a field experiment was conducted including forty-eight genotypes which were grown in upland conditions and evaluated for their response to Si rates and reduction on grain discoloration. The relationship between Si rates and grain discoloration was quadratic negative. Weight of filled grains per panicle increased as the Si rates in the soil increased. Genotypic differences for Si concentration in husk were evident for both non-amended and Si-amended plots. While the Si concentration in husk increased to all genotypes, there was no relationship between grain discoloration and Si concentration in husk for plants from non-amended and Si-amended plots. The genotype CAN-7024 with the highest resistance to leaf brown spot also showed the lowest grain discoloration in comparison to the genotypes Casado and Caqui.

Resumo em Inglês:

The fungus Corynespora cassiicola is an important pathogen that causes necrotic lesions in several plant species. Saprophytism and parasitism habits of plants are common survival strategies for this pathogen. Few studies referred to the formation of chlamydospores by C. cassiicola. The objective of this study was to test the formation of chlamydospores by several C. cassiicola isolates from different agronomic crops and weeds. Fifteen isolates were analysed by in vivo and in vitro tests. Six isolates from four host plants (Cucumis sativus, Lantana camara, Malpighia glabra and Vernonia cinerea) were able to produce chlamydospores, both in vitro and in vivo. In vitro, chlamydospore production was highest for the Malpighia glabra isolate and one Cucumis sativus isolate, intermediate for two other C. sativus isolates, and lowest for the Vernonia cinerea and Lantana camara isolates. However, no difference in the relative number of chlamydospores produced among isolates was observed in vivo.

Resumo em Inglês:

Fusarium head blight (FHB) of wheat, is caused by fungal populations belonging to the Fusarium graminearum species complex. Although triazole fungicides are widely used in FHB management, information about the sensitivity of F. graminearum populations to such fungicides is scarce, particularly in Brazil. This work aimed at determining the sensitivity of pathogenic populations of F. graminearum to metconazole and tebuconazole. Fungal isolates were obtained from diseased wheat heads collected in commercial fields at the northern region of Rio Grande do Sul state, Brazil, along the 2009 and 2010 growing seasons. Fifty isolates obtained from eleven locations were grown in media amended with increasing fungicide dosages and the effective concentration reducing mycelial growth to 50% (EC50) was determined. The median of the EC50 values was 0.001 mg/L (<0.001-0.152 mg/L) and 0.037 mg/L (<0.001-0.324), for tebuconazole and metconazole, respectively. Cross-resistance was detected based on significance of correlation analysis (r s = 0.46; P < 0.0001) between the log-transformed EC50 of the two triazoles. The mean EC50 for a group of ten isolates classified as "more sensitive" differed statistically from the ten isolates representing the "less sensitive" group. Nevertheless, these groups did not differ in terms of mycelial growth on PDA in the absence of fungicides. It was concluded that pathogenic populations of F. graminearum are sensitive to the triazoles at various levels due to the intrinsic characteristics of the isolates or to selection pressure by the increasing fungicide use.

Resumo em Inglês:

Coffee leaf rust (CLR), caused by the fungus Hemileia vastatrix, is among the most important diseases affecting coffee all over the world. In Kenya, it is currently the second most important disease, and breeding coffee to obtain new resistant cultivars has been a priority. Over time, new rust pathogenic races able to infect hitherto resistant coffee genotypes have been registered. To date, 49 races of the pathogen have been characterized all over the world. The most recent races to be characterized are able to infect derivatives of Timor Hybrid (HDT), which is a major source of resistance in breeding programs. This work aimed to identify new races of the pathogen in Kenya, emphasizing infected leaves sampled from CLR resistant varieties and breeding lines collected from two sites (Ruiru and Koru). Twenty-four samples were characterized, out of which 22 samples corresponded to new races of the pathogen. A total of six new races (III, XVII, XXIII, XXXVI, XLI and XLII) were characterized, revealing three new virulence genes (v1, v7, v8) and possibly a fourth virulence gene, the v9. This finding represents a serious threat to coffee production and also a challenge to coffee breeding programs that are in progress in Kenya.

Resumo em Inglês:

A severe leaf and stem necrosis disease of Alternanthera philoxeroides (alligatorweed) was examined in the summer of 2011. Symptoms on leaves and stems of A. philoxeroides consisted of round to oval straw colored spots with maroon margins resulting in chlorosis, severe defoliation and withering of stems. The causal pathogen isolated on V-8 agar medium was morphologically identified as Nimbya alternantherae. Pathogenicity of N. alternantherae was proven on healthy A. philoxeroides plants. This is the first report of A. philoxeroides necrosis caused by N. alternantherae in Pakistan.

Resumo em Português:

O polissacarídeo algal ulvana induz resistência em macieira à mancha foliar de Glomerella. Porém, modificações no processo pré-infeccioso de Colletotrichum gloeosporioides vêm sendo relatadas em plantas previamente tratadas com ulvana. Assim, este trabalho objetivou verificar se o polissacarídeo interfere diretamente no desenvolvimento de estruturas pré-infectivas. Para tanto, depositou-se gotas de 10 µL de suspensão de 2x10(5) conídios.mL-1 em segmentos de papel celofane, assentados sobre lâminas de vidro. A suspensão conidial foi preparada com solução aquosa contendo ou não ulvana (10 mg.mL-1). As amostras foram incubadas a 25ºC e 100% de humidade relativa. A cada duas horas, 100 conídios por gota foram examinados microscopicamente (200x), por um período de 16h. As taxas de germinação de conídios, formação e melanização de apressórios foram quantificadas. A germinação dos conídios não foi afetada. Ulvana estimulou o alongamento do tubo germinativo, mas retardou a diferenciação do primeiro apressório (séssil). O polissacarídeo acelerou a formação do segundo apressório, mas inibiu a sua melanização.

Resumo em Inglês:

The algal polysaccharide ulvan induces resistance in apple to Glomerella leaf spot. However, changes in the pre-infectious process of Colletotrichum gloeosporioides have been reported in apple plants previously treated with ulvan. Thus, this study aimed to verify if the polysaccharide interferes directly in the development of pre-infective structures. For this, 10 µL drops of spore suspension (2x10(5) conidia.m L-1) were distributed on cellophane paper segments settled on glass slides. The conidial suspension was prepared with aqueous solution with (10 mg.mL-1) or without ulvan. Samples were incubated at 25ºC and 100% relative humidity. At every two hours of incubation and over a period of 16 hours, 100 conidia per drop were microscopically (200x) examined. The rates of conidia germination, apressoria formation and melanization were quantified. Germination of conidia was not affected. Ulvan stimulated the elongation of the germ tube but retarded the differentiation of the first apressorium (sessile). The polysaccharide accelerated the formation of second apressorium, but inhibited its melanization.