The objective of this work was to assess the virulence to lettuce cultivars and host specificity and to identify races of Fusarium oxysporum f. sp. lactucae (FOLac) isolates associated with lettuce wilt in Brazil. Thirty-one isolates identified based on morphology were inoculated in a set of lettuce cultivars for race determination. Plantlets of 'Elisa', 'Vera', and 'Red Salad Bowl' cultivars were inoculated with all isolates using a root-dipping method. Isolates were also inoculated in species of Asteraceae and other botanical families. 'Elisa' and 'Vera' were susceptible to 27 isolates while 'Red Salad Bowl' was resistant to all isolates. Plants other than lettuce were not infected by any of the isolates, suggesting their specificity to lettuce. All pathogenic isolates were assigned to race 1 and used to evaluate a PCR protocol with primers targeting race 1. Only amplicons associated with race 1 pattern were observed for all pathogenic isolates but not for one non-pathogenic isolate, thus leading us to conclude that FOLac race 1 is so far the sole causal agent of lettuce wilt in Brazil.

The objective of this study was to estimate the reduction in yield caused by Colletotrichum graminicola in resistant and susceptible maize hybrids inoculated at different stages of development. Two trials were conducted in different environmental conditions in a randomized block design with treatments arranged as a 2 × 5 factorial scheme and three replications. Treatments consisted of two hybrids (H8664, resistant and H8621, susceptible) inoculated at three growing stages (8-leaf, 12-leaf and tasseling stage). Internal lesion length, adjusted yield, and yield components (length, diameter and ear weight) were evaluated 120 days after emergence. Significant differences in yield and ear weight were detected in the susceptible hybrid inoculated at the earliest stage: yield was reduced by 16.1 and 20.2% in the first and second experiment, respectively. Although lesion length in the susceptible hybrid was approximately three times greater than in the resistant, there were no significant differences in lesion length among treatments for each hybrid. However, there were differences in the number of dead plants and ear weight. It is suggested that damage caused by early infection with C. graminicola results mainly from plant death and reduction in ear weigh rather than from the extent of colonization of the stalk.

Isolates of Cercospora species from leaves displaying symptoms of grey leaf spot were collected in maize-producing areas of south-central Brazil in 2001 and 2002. Restriction digests of the internal transcribed spacer region of rDNA detected the presence of the same two Cercospora species described on maize in the United States, namely C. zeae-maydis and the recently described species, C. zeina . Genetic variability among isolates was assessed by analysing 104 amplified fragment length polymorphism loci. Cluster analysis confirmed the genetic separation of isolates into two species with a mean similarity of 35%. Similarity levels within species were high, averaging 93% and 92% among isolates of C. zeae-maydis and C. zeina , respectively. The mean genetic similarity between C. zeae-maydis and C. zeina and two isolates of C. sorghi f. sp. maydis was 45% and 35%, respectively. Results of this study showed that populations of the grey leaf spot pathogens in Brazil are similar to those in the United States regarding species composition and that C. zeina is also present in Brazil.

O sucesso do estabelecimento de uma relação parasitária entre fungos e plantas, em muitos casos, depende de eventos que antecedem à infecção. Neste trabalho, as fases compreendidas entre a germinação e a penetração do fungo Stenocarpella macrospora foram analisadas por meio de microscópio eletrônico de varredura. Para tanto, plantas de milho (Zea mays) híbrido Das-8492, suscetível à mancha foliar de diplodia, foram cultivadas em casa de vegetação e inoculadas com 300 µl de uma suspensão de 10(5) conídios/ml ao atingirem cinco-seis folhas expandidas. As amostras foram obtidas a partir de discos foliares coletados em vários momentos após a inoculação e preparadas para análise ao microscópio eletrônico de varredura. Oitenta e seis por cento dos conídios germinaram entre 12 e 15 h após a inoculação, ao passo que a formação dos apressórios ocorreu 18 h após a inoculação. A presença de uma matriz extracelular também foi observada desde a germinação até a penetração do patógeno, sugerindo a participação da mesma nos processos relacionados à patogênese.

The success of a parasitic relationship between fungal pathogens and their host plants depends on pre-infectional events. In this work scanning electron microscopy was used to study the events that occur between germination and penetration of the fungus Stenocarpella macrospora on maize (Zea mays) leaves. Plants of the hybrid Das-8492 were cultivated in greenhouse, and inoculated at the five-six leaves stage with 300 µl of a conidial suspension of 10(5) conidia/ml. Disk samples of leaf tissue were collected at different times after inoculation and prepared for analysis by scanning electron microscopy. It was verified that 86% of the conidia germinated between 12-15 h whereas apressoria formation occurred 18 h after inoculation. The presence of an extra cellular matrix also was observed during germination and penetration, suggesting that it may have a role in pathogenesis.

Este trabalho objetivou identificar marcadores microssatélites ligados a genes de resistência a Puccinia polysora e verificar o efeito fenotípico destes nas variáveis monocíclicas número e comprimento de lesão. Foram utilizadas duas linhagens (Z-95 e Z-93) contrastantes em níveis de resistência à doença, o híbrido (Z-95 x Z-93) e uma população F2 obtida da autofecundação deste. Esses indivíduos foram fenotipados para resistência à doença em dois ensaios a campo e genotipados para 142 marcadores microssatélites. Para agilizar a genotipagem, o método de análise de segregantes agrupados (ASA) foi utilizado. Marcadores potencialmente ligados a genes de resistência identificados por este método foram utilizados para genotipar 165 indivíduos segregantes e confirmar a existência de ligação. Dois marcadores, Phi 65 e Phi 28, ambos no cromossomo 9, mostraram-se significativamente associados (p<0,000001 e p<0,000078, respectivamente) a um QRL (locos de resistência quantitaviva) a P. polysora. A associação entre QRL e marcadores explicou, respectivamente, 12,9% e 5,10% da variação fenotípica para resistência. Em um terceiro ensaio em casa de vegetação, 94 plantas foram inoculadas com suspensão de uredósporos e avaliadas 15 dias após a inoculação quanto ao número de lesões e o comprimento de dez lesões. Estas plantas foram genotipadas com os marcadores Phi 65 e Phi 28. Somente Phi 65 mostrou-se significativamente associado (P< 0,000032) à redução no número de lesões. Nenhum marcador mostrou associação significativa com a variável comprimento de lesão. Por estarem ligados ao mesmo marcador, sugere-se que o QRL identificado nos ensaios a campo seja o mesmo identificado em casa de vegetação.

The objectives of this study were to identify microsatellite markers linked to resistance gene of resistance to Puccinia polysora and to estimate the phenotypic effect of these genes on two monocyclic variables lesion, number and length. Two inbreed lines with different degrees of resistance (Z-95 and Z-93), the hybrid (Z-95 X Z-93) and F2 plants derived by selfing this hybrid were phenotyped for disease resistance, in two field trials and genotyped for 142 microsatellite markers using bulked segregant analysis (BSA). The molecular markers putatively linked to the disease resistance genes identified by this method were used to genotype 165 segregant individuals and to confirm linkage. Two markers, Phi 65 and Phi 28, both located on chromosome nine, were significantly associated (p<0.000001 and p<0.000078) with a QRL (quantitative resistance loci) to P. polysora. The association explained 12.9 and 5.10% of the phenotypic variance in resistance for Phi 65 and Phi 28, respectively. In a third trial performed in the greenhouse, 94 plants were inoculated with a uredospore suspension and evaluated 15 days after inoculation for the total number of lesions and the length of ten lesions. These plants were genotyped with Phi 65 and Phi 28. Only Phi 65 showed a significant association with lesions number (p<0.000032). No marker showed significant association with lesion length. It is suggested that the QRL identified in the field trials is the same identified in the greenhouse experiment, since they are linked to the same marker.

Em experimento realizado em casa de vegetação com quatro linhagens e dois híbridos de milho (Zea mays), verificou-se variabilidade para resistência a queima foliar causada por Colletotrichum graminicola avaliada por meio das variáveis área total de lesão por planta (ATL), área média de lesão (AML), comprimento total de lesão por planta (CTL), comprimento médio de lesão (CML) e número de lesões por planta (NL). Quando dois isolados de C. graminicola foram inoculados nessas linhagens e em híbridos de milho não foi verificada interação diferencial entre isolados e genótipos do hospedeiro. Em estudos de herança da resistência, as linhagens genitoras L186 e L64 comportaram-se como suscetível e resistente, respectivamente, ao passo que o híbrido L186 x L64 apresentou resistência. A análise das freqüências observadas de plantas resistentes e suscetíveis na população F2 resultantes da autofecundação do híbrido, indicou ocorrência de herança monogênica com dominância completa para o alelo que confere resistência à doença.

Variability in resistance to corn (Zea mays) leaf anthracnose caused by Colletotrichum graminicola was detected among four lines and two hybrids for the variables: total area of lesion (ATL), average lesion area (AML), total lesion length (CTL), average lesion length (CML) and lesion number (NL). No differential interaction was detected among isolates of C. graminicola and inbred lines and hybrids. In studies about the mode of resistance to foliar anthracnose, the inbred lines L186 and L64 were susceptible and resistant, respectively, whereas the hybrid L184 x L64 were resistant. The observed frequency of susceptible and resistant F2 plants derived from selfing of F1 plants from the cross L186 x L64 indicated monogenic and dominant control of resistance