Witches' broom disease of cocoa: genome organization, genetic variability and anlysis of the identity and expression of pathogenicity genes of the fungal pathogen Crinipellis perniciosa

Author(s)

Johana Rincones

• Document type: Doctoral Thesis
• Press: Campinas, SP. , ilustrações.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2006-04-03

Examining board members

Gonçalo Amarante Guimarães Pereira; Maria Sueli Soares Filipe; Nilce Maria Martinez Rossi; Marcelo Menossi; Michel Georges Albert Vincentz; Jose Camillo Novello

• Advisor: Gonçalo Amarante Guimarães Pereira
• Field of knowledge: Biological Sciences - Biochemistry
• Indexed in: Base Acervus-UNICAMP; Biblioteca Digital da UNICAMP
• Location: Universidade Estadual de Campinas. Biblioteca Central Cesar Lattes; T/UNICAMP; R471v; Universidade Estadual de Campinas. Biblioteca do Instituto de Biologia; T/UNICAMP; R471v

Abstract

Witches' broom disease of cocoa is a complex pathosystem that has evaded an efficient control program in the cacao-producing region of Bahia, Brazil. The main goal of this work was to acquire a better understanding of the C. perniciosa-Cacao interaction by providing new data regarding: 1) the size and organization of the fungal genome through molecular karyotyping; 2) the genetic variability of this phytopathogen at the chromosomal level in the cacao-producing region of Bahia; and 3) the gene expression of the fungus in the presence of host extracts. The molecular karyotype was obtained through pulsed-field gel electrophoresis. This same technique was applied in combination with microsatellite PCR analysis of 38 isolates from different biotypes and geographic regions in order to study the chromosomal-level genetic variability of this pathogen. For the gene expression analysis, four cDNA libraries of the fungus grown under different culture conditions and developmental stages, including a subtractive library using SSH, were sequenced and searched for similarities in the public databases. As results, we present the molecular karyotype of C. perniciosa and the existence of chromosome-length polymorphism. The analysis of the 38 isolates showed that the karyotype of the C-biotype is very stable in time and that the variability of the pathogen in Bahia is very low, thus indicating the fragility of the current cacao-breeding program in Bahia, where the resistant cacao clones selected in the field were challenged against only two different genotypes of the pathogen. With regards to the gene expression analysis, we obtained 1427 unigenes and the similarity searches allowed the identification of various mechanisms through which the fungus might be manipulating the metabolism of the plant for its own benefit and in detriment of cocoa production. Therefore, we consider that this work allowed us to acquire a better understanding of the molecular mechanisms used by C. perniciosa during witches' broom development in cacao and more detailed studies, based on the results presented here, might aid in the development of novel control strategies for this important disease (AU)