L. M. Costamilan

Pathogenicity, molecular characterization, and cercosporin content of Brazilian isolates of Cercospora kikuchii

Cercospora kikuchii esta envolvido na desfolha da soja (Glycine max), normalmente em associacao com Septoria glycines, no final do ciclo da cultura. Setenta e dois isolados, obtidos principalmente de sementes com mancha purpura e oriundas de diferentes regioes do Brasil, mostraram variabilidade fenotipica. O teor de cercosporina e a velocidade de crescimento de colonias foram bastante variaveis entre os isolados. Uma forte correlacao foi identificada entre o teor de cercosporina e virulencia. Diferencas geneticas, entre e dentro da populacao analisada, foram observadas por RAPD com a analise de 86 loci. As analises de RAPD permitiram agrupar os isolados em sete grupos. Nenhuma relacao foi identificada entre os grupos de RAPD e a origem geografica ou teor de cercosporina. A sequencia da regiao espacadora do DNA ribossomal (ITS1-5,8S-ITS2) foi determinada em 13 isolados escolhidos nos diferentes agrupamentos. A similaridade das sequencias obtidas comparadas as sequencias de C. kikuchii depositadas no GenBank (AY266160, AY266262, AY152577 e AF291708) variou de 97 a 100%. Este trabalho demonstrou que os isolados brasileiros de C. kikuchii de diferentes origens sao variaveis quanto a virulencia, aos padroes de RAPD e ao teor de cercosporina. O teor de cercosporina pode ser um bom parâmetro na escolha de um isolado adequado para selecao de cultivares tolerantes ou resistentes a esse patogeno. Considerando que ele e facilmente transmitido por sementes nao e surpresa encontrar os mesmos haplotipos em diferentes regioes. A migracao poderia ser favorecida por sementes infetadas como demonstrado na analise de RAPD.

Variability of the wheat powdery mildew pathogen Blumeria graminis f. sp. tritici in the 2003 crop season

Wheat (Triticum aestivum) powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici, is one of the most severe foliar diseases attacking this crop, reducing grain yields by 10% to 62% in Brazil. The disease can be controlled by genetic resistance of the host, but the pathogen has physiological specialization, which enables it to infect wheat cultivars that have remained resistant for years. The objective of this work was to evaluate the variability of pathogenic strains of B. graminis f. sp. tritici collected in Brazil and the effectiveness of wheat resistance genes to powdery mildew in the 2003 crop season. Plants of a differential series were inoculated with each monopustular isolate. Thirty-one combinations of effective and ineffective resistance genes were identified. Only the gene Pm4a+... remained totally effective to all isolates, and gene Pm6 was highly effective (below 10% of susceptibility), whereas genes Pm3a and Pm8 were totally ineffective (susceptible to all isolates). Genes Pm3c, D1, and D2 showed low effectiveness (above 50% of susceptibility), and genes Pm1, 2, 4a, 1+?, and 2+Mld had mean effective results to most strains (susceptibility between 10% and 49%). The virulence formula Pm1, 3c, 4a, 6, 1+?, 2+Mld, 4a+..., D2 (effective genes) / 2, 3a, 8, D1 (ineffective genes) was most frequently found, accounting for 15% of the occurrences. The most frequent number of ineffective genes was seven, ranging from three to ten.

Ferrugem-asiática da soja no Brasil: passado, presente e futuro

Asian soybean rust, caused by the fungus Phakopsora pachyrhizi , is the most severe disease of the crop and can cause yield losses of up to 90%. The disease was first reported in Brazil in 2001. Epidemics of the disease are common in the country, where the fungus can survive year‑round. Regulatory measures to reduce the inoculum between seasons and avoid late-season soybean have been adopted to manage the disease. Disease control has relied mainly on chemical control, but a lower sensibility of the fungus to fungicides has been reported in Brazil. Major‑resistance genes have been mapped and incorporated into the cultivars. With the reduced efficacy of the fungicides, the adoption of integrated measures to control the disease will be important for the sustainability of the crop. This review presents the main changes in the soybean crop system caused by the introduction of the fungus in Brazil, the current management strategies adopted to avoid losses, and the new trends that, together with biotechnological strategies, can improve management in the future.

First report of Diaporthe phaseolorum var. caulivora infecting soybean plants in Brazil

In March 2006, diseased soybean plants (Glycine max) were found in the municipalities of Passo Fundo and Coxilha, state of Rio Grande do Sul, Brazil, showing withered, brown leaves and light to reddish-brown discoloration and necrosis (canker) of the lower half of the stem. Cultural characteristics in potato dextrose agar showed identical patterns to those described for Diaporthe phaseolorum varcaulivora (Dpc). The rDNA-ITS sequence data from the Brazilian strain CH 40/06 (GenBank accession number EU622854) were compared to homologous sequences from the NCBI GenBank database, and a high similarity with Dpc strains was verified. A phylogenetic reconstruction was performed to compare EU622854 with other related sequences and grouped with Dpc. This group was highly supported by the bootstrap test (99%). Morphology of the Brazilian specimen was also similar to that described in the literature for Dpc, but the ascospores were slightly narrower than the American original material of Dpc. In field surveys performed in the 2006/07 crop season, Dpc was also found in five additional municipalities in RS.

Efetividade de genes de resistência de trigo a oídio

Levantamentos periodicos da frequencia de virulencia do patogeno causador de oidio (Blumeria graminis f. sp. tritici) em trigo (Triticum aestivum)auxiliam na escolha de fontes de resistencia para uso em cruzamentos. Este trabalho relata resultados de cinco anos de verificacao de efetividade de genes de resistencia para populacoes patogenicas de B. graminis f. sp. tritici oriundas do Brasil e do Chile. Amostras de oidio foram recebidas pela Embrapa Trigo, Passo Fundo, RS, em 1995, 1996, 1997, 1999 e 2000. Inoculou-se cada isolado monopustular em plantas de trigo da serie diferencial para racas. Foram identificadas 90 combinacoes diferentes de genes efetivos e inefetivos para resistencia. Em 1995 e 1997, a maioria dos isolados foram virulentos com relacao aos genes Pm3a, Pm3c, Pm8, Pm1+... e PmD1; em 1999, para Pm3a, Pm3c, Pm4b, Pm8, PmD1 e PmD2; e, em 2000, para Pm3a, Pm3c, Pm4b, Pm6, Pm8, PmD1 e PmD2. Em todos os anos analisados, permaneceram efetivos a todos os isolados os genes Pm2 e Pm4a+.... O numero de genes inefetivos por isolado variou entre um e nove, no total de 13 genes ou combinacoes de genes testados. Isolados apresentando virulencia a cinco genes ou combinacoes foram mais frequentes em 1995 e em 1997, a seis em 1999 e a sete em 2000, o que pode significar aumento na complexidade da composicao racial do patogeno a cada ano.

BRS 374 - wheat cultivar

BRS 374 is a wheat cultivar developed by Embrapa. It resulted from a cross between the F1 generation of PF 88618/Coker80.33 and Frontana/Karl. BRS 374 belongs to the soft wheat class, has a low plant height, a high potential grain yield, and white flour.