Biologia e estrutura genética de populações do patógeno da brusone do trigo no centro-sul do Brasil
Carregando...
Data
2016-08-23
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
Na primeira parte de nosso estudo descrevemos a associação de Pyricularia pennisetigena e P. zingibericola a gramíneas invasoras de áreas de trigo no centro-sul do Brasil. Desconhece-se, entretanto, qual o potencial de P. pennisetigena e P. zingibericola como patógenos de poáceas de interesse econômico para a agricultura brasileira. Dessa forma, objetivamos caracterizar o espectro de patogenicidade de P. pennisetigena e P. zingibericola a braquiária, cevada e trigo e compará-lo com P. grisea e com a espécie até recentemente descrita como P. oryzae patotipo Triticum, de ocorrência generalizada no agroecossistema brasileiro. Foram testados 20 isolados de Pyricularia spp. obtidos de amostras de folhas infectadas de plantas invasoras de campos de trigo. A classificação dos isolados em espécies distintas de Pyricularia foi efetuada usando-se filogenia molecular baseada nas sequencias parciais dos genes actina e calmodulina. Pyricularia pennisetigena e P. zingibericola inoculadas em folhas, foram patogênicas a braquiária, cevada e trigo, com diferenças na agressividade entre as espécies. Pyricularia zingibericola foi a espécie mais agressiva a braquiária e cevada, enquanto P. pennisetigena foi a espécie mais agressiva em plantas jovens de trigo. Por outro lado, P. grisea isolada de Digitaria sanguinalis ou de Urochloa spp. não infectou trigo. A análise filogenética das regiões ACT e CAL concatenadas reproduziu as relações filogenéticas e a magnitude das diferenças descritas entre Pyricularia zingibericola, P. pennisetigena, P. oryzae patotipo Triticum e P. grisea. Urochloa spp. provavelmente representam fonte permanente de inóculo inicial dos patógenos da brusone do trigo entre as épocas de cultivo. Na segunda parte desta pesquisa, foi estudado a estrutura genética de populações do patógeno da brusone do trigo, o fungo Ascomiceto Pyricularia graminis-tritici sp. nov., no centro-sul do Brasil. Os objetivos foram responder às seguintes perguntas: As populações geograficamente distintas de P. graminis-tritici do trigo eram geneticamente subdivididas? Como se distribuía a diversidade gênica e genotípica entre as populações regionais de P. graminis-tritici, cerca de 30 anos após as primeiras epidemias de brusone no Brasil? Qual o sistema reprodutivo predominante de P. graminis-tritici no país? Conclui-se que não houve subdivisão na maioria das populações geográficas contemporâneas de P. graminis-tritici do trigo, indicando mecanismo eficiente de fluxo gênico. A magnitude e a extensão do fluxo gênico entre populações geográficas de P. graminis-tritici do trigo, o sistema reprodutivo predominantemente sexual, aliados a alta diversidade genética do fungo, indicam um patógeno com alto potencial evolutivo no agroecossistema brasileiro. Outras espécies de poáceas hospedeiras com ampla distribuição geográfica no Brasil, como por exemplo, o capim-braquiária (Urochloa brizantha), podem ter importante papel no ciclo de vida e na biologia reprodutiva, na sobrevivência e na dispersão do inóculo de P. graministritici a curta e longa distâncias, mantendo as populações geográficas do patógeno conectadas. Os padrões de fluxo gênico e genotípico entre populações hospedeiro-distintas do patógeno reforçam a hipótese de que a brusone do trigo pode ter tido origem de novo a partir de populações endêmicas de P. graminis-tritici que infectam outras espécies de poáceas (nativas ou invasoras de áreas de trigo) no país.
In the first part of our study we described the association of Pyricularia pennisetigena and P. zingibericola with invasive grasses from wheat cropping areas in South-Central Brazil. However, the potential of P. pennisetigena and P. zingibericola as pathogens to poaceous plants of economic interest for Brazilian agriculture is still unknown. Therefore, this study aimed to characterize the pathogenicity spectrum of P. pennisetigena and P. zingibericola to signal grass, barley and wheat and compare with P. grisea and with the species until recently described as P. oryzae pathotype Triticum, of widespread occurrence in the Brazilian agroecosystem. Twenty isolates of Pyricularia spp. obtained from samples of infected leaves of weed species in wheat fields were tested. Classification of isolates into different species of Pyricularia was performed using molecular phylogeny based on the partial actin and calmodulin gene sequences. Pyricularia pennisetigena and P. zingibericola inoculated on leaves were pathogenic to signal grass, barley and wheat, with differences in aggressiveness between species. Pyricularia zingibericola was the most aggressive species to signal grass and barley, while P. pennisetigena was the most aggressive species to young plants of wheat. On the other hand, P. grisea isolated from Digitaria sanguinalis or Urochloa spp. did not infect wheat. Phylogenetic analysis of the concatenated regions ACT and CAL reproduced the phylogenetic relationships and the magnitude of the differences reported between Pyricularia zingibericola, P. pennisetigena, P. oryzae pathotype Triticum and P. grisea. Urochloa spp. probably represents a permanent source of initial inoculum of the wheat blast pathogens between growing seasons. In the second part of this research, we studied the genetic structure of populations of the wheat blast pathogen, the Ascomycete fungus Pyricularia graminis - tritici sp. nov., in the South-Central Brazil. The objectives were to answer the following questions: The geographically distinct populations of P. graminis-triticiwheat were genetically subdivided? How gene and genotypic diversity were distributed among regional populations of P. graminis-tritici about 30 years after the first outbreaks of wheat blast in Brazil? What is the predominant reproductive system of P. graminis-tritici in the country? We concluded that there was no subdivision among most of the contemporary geographical populations of Pyricularia graminis- tritici from wheat fields, indicating an efficient mechanism of gene flow. The magnitude and extent of gene flow among geographical populations of P. graminis-tritici, the predominantly sexual reproductive system, coupled with high genetic diversity of the fungus, indicated a pathogen with high evolutionary potential in the Brazilian agro-ecosystem. Other species of poaceous hosts with wide geographic distribution in Brazil, for example, signal grass (Urochloa brizantha) can play an important role in the life cycle and reproductive biology, survival and spread of inoculum of P. graminis- tritici at short and long distances, keeping the geographical populations of the pathogen connected. The patterns of gene and genotypic flow between host-distinct populations of the pathogen reinforce the hypothesis that the wheat blast may had a de novo origin from endemic populations of P. graminis-tritici infecting other poaceous species (native or invasive WRwheat areas) in the country.
In the first part of our study we described the association of Pyricularia pennisetigena and P. zingibericola with invasive grasses from wheat cropping areas in South-Central Brazil. However, the potential of P. pennisetigena and P. zingibericola as pathogens to poaceous plants of economic interest for Brazilian agriculture is still unknown. Therefore, this study aimed to characterize the pathogenicity spectrum of P. pennisetigena and P. zingibericola to signal grass, barley and wheat and compare with P. grisea and with the species until recently described as P. oryzae pathotype Triticum, of widespread occurrence in the Brazilian agroecosystem. Twenty isolates of Pyricularia spp. obtained from samples of infected leaves of weed species in wheat fields were tested. Classification of isolates into different species of Pyricularia was performed using molecular phylogeny based on the partial actin and calmodulin gene sequences. Pyricularia pennisetigena and P. zingibericola inoculated on leaves were pathogenic to signal grass, barley and wheat, with differences in aggressiveness between species. Pyricularia zingibericola was the most aggressive species to signal grass and barley, while P. pennisetigena was the most aggressive species to young plants of wheat. On the other hand, P. grisea isolated from Digitaria sanguinalis or Urochloa spp. did not infect wheat. Phylogenetic analysis of the concatenated regions ACT and CAL reproduced the phylogenetic relationships and the magnitude of the differences reported between Pyricularia zingibericola, P. pennisetigena, P. oryzae pathotype Triticum and P. grisea. Urochloa spp. probably represents a permanent source of initial inoculum of the wheat blast pathogens between growing seasons. In the second part of this research, we studied the genetic structure of populations of the wheat blast pathogen, the Ascomycete fungus Pyricularia graminis - tritici sp. nov., in the South-Central Brazil. The objectives were to answer the following questions: The geographically distinct populations of P. graminis-triticiwheat were genetically subdivided? How gene and genotypic diversity were distributed among regional populations of P. graminis-tritici about 30 years after the first outbreaks of wheat blast in Brazil? What is the predominant reproductive system of P. graminis-tritici in the country? We concluded that there was no subdivision among most of the contemporary geographical populations of Pyricularia graminis- tritici from wheat fields, indicating an efficient mechanism of gene flow. The magnitude and extent of gene flow among geographical populations of P. graminis-tritici, the predominantly sexual reproductive system, coupled with high genetic diversity of the fungus, indicated a pathogen with high evolutionary potential in the Brazilian agro-ecosystem. Other species of poaceous hosts with wide geographic distribution in Brazil, for example, signal grass (Urochloa brizantha) can play an important role in the life cycle and reproductive biology, survival and spread of inoculum of P. graminis- tritici at short and long distances, keeping the geographical populations of the pathogen connected. The patterns of gene and genotypic flow between host-distinct populations of the pathogen reinforce the hypothesis that the wheat blast may had a de novo origin from endemic populations of P. graminis-tritici infecting other poaceous species (native or invasive WRwheat areas) in the country.
Descrição
Palavras-chave
Triticum aestivum, Pyricularia graminis-tritici, Patogenicidade, Hospedeiros, Estudo genético-populacional, Pathogenicity, Hosts, Population genetic study