AnÃlise da diversidade genÃtica e patogÃmica de Mycosphaerella fijiensis e Mycosphaerelle musicola no Brasil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

Black and yellow Sigatoka diseases, caused by the fungi Mycosphaerella fijiensis and M. musicola, respectively, are responsible for important losses in banana production all over the world. The former disease is distributed over the whole Brazilian territory, with the exception of the Northeast region and the sates of Rio de Janeiro, EspÃrito Santo, GoiÃs and Tocantins, while the latter is found all over the country. The knowledge of the genetic diversity of both fungi is central for the development of suitable control strategies and has been achieved at local, regional, continental and global levels by the use of molecular markers. The detection of pathogenic diversity also contributes to the understanding of their population dynamics and strategies for their occurrence in new regions. In Brazil there is presently no information on these issues. This study was aimed at the evaluation of M. fijiensis genetic and pathogenic diversity in Brazil Northern region and Mato Grosso State at the analysis of the genetic variability of M. musicola isolates from Pernambuco state, the second largest Brazilian banana producer, where the fungus has been prevalent for many decades. To reach this objective there was initially the need to previously optimize a new culture system that could induce and sustain an adequate growth of M. musicola mycelia in vitro, based on the evaluation of different combinations of culture media, nitrogen and carbon sources, pH values and light regimens. DBA/IFB proved to be the best, with its final pH value adjusted to 5.7 and the cultures kept in the dark. The genetic diversity of 28 M. musicola isolates were subsequently analyzed using RAPD, with the generation of 78 bands, 24 of them polymorphic; a high genetic variability was demonstrated among isolates from nine Pernambuco State counties, without an apparent correlation between the observed diversity and the geographic origin of the isolates. When the diversity of M. fijiensis was similarly assessed, 184 bands were obtained, with 158 polymorphic. Cluster analysis points to a high genetic variability among groups, as well as a low diversity within groups. These conclusions were confirmed by the analysis of AFLP haplotypes, following the analysis of 298 bands, 264 being polymorphic, for 42 isolates. M. fijiensis genetic diversity was also evaluated by the analysis of rDNA ITS sequences and confirm most of the conclusions drawn above on the basis of the former techniques, although a much lower polymorphism level was detected (only 4 positions in both ITS sequences). Both analyses were unable o define a clear correlation between a genetic pattern and the geographic origin of the isolate, but the analysis of AFLP markers and, to a lesser extent, of RAPD markers, proved to be a powerful tool for the study of intra-specific genetic diversity of M. fijiensis. Pathogenic diversity among M. fijiensis isolates was also demonstrated by the use of experimental infection of cultivars bearing different susceptibilities to the fungus. The individual reactions of isolate-host genotypes pointed towards the existence of an important pathogenic diversity among Brazilian M. fijiensis isolates. The rapid spread of M. fijiensis in Brazil, associated to the fungus increased genetic recombination rates and the high level of genetic diversity of M. musicola in Pernambuco are worrisome factors for the local farmers, as costs for their control would be hardly covered by the small producers in the state, employing only highly susceptible cultivars for both yellow and black Sigatokas

ASSUNTO(S)

diversidade genÃtica tÃcnicas aflp (amplified fragment length polymorfism) its (internal transcribed spac) rapd (random amplified polymorphic dna) ciencias biologicas mycosphaerella fijiensis (sigatoka negra)

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