|Schnell ii, Raymond|
Submitted to: European Journal of Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/9/2004
Publication Date: 4/15/2005
Citation: Ploetz, R.C., Schnell II, R.J., Ying, Z., Zheng, Q., Olano, C.T., Johnson, E. 2005. Analysis of molecular diversity in Crinipellis perniciosa with AFLP markers. European Journal of Plant Pathology. 111/4, pp. 317-326. Interpretive Summary: The pathogen of cacao that causes the disease known as witches' broom is caused by the fungus Crinipellis perniciosa. This disease has severely limited production of cocoa beans in South America. The USDA-ARS has a breeding program to develop varieties of Theobroma cacao resistant to the disease, based at the Miami station. In order to more effectively develop the breeding program an understanding of the genetic diversity in the pathogen population is essential. To this end molecular markers were used to characterize and compare 41 isolates from nine locations in South America. The 41 isolates contained 15 unique genotypes and most of these were very similar with a similarity coefficient of 72%. The analysis grouped the isolates from Brazil, Bolivia, Trinidad, and Ecuador into a major cluster with high levels of statistical support. The molecular information provided support for field observations of two separate introductions of the pathogen in the state of Bahia in Brazil.
Technical Abstract: Crinipellis perniciosa causes a serious disease of cacao, witches¿ broom. Genetic diversity among 41 isolates of the pathogen was analyzed with arbitrary fragment length polymorphisms (AFLPs). Nine of 64 primer pairs that were tested produced consistent and informative DNA amplification, and were used to screen all accessions. Fifteen haplotypes (AFLP fingerprints) were apparent with the 186 polymorphic loci that were detected. Although cluster and principal component analyses (PCA) grouped isolates of the C biotype from Bolivia, Brazil, Ecuador and Trinidad together in a major cluster that was distinct from an isolate of the S biotype, differentiation was observed among isolates of the C biotype from different countries. High levels of bootstrap support were found for each grouping and 72% of the total variance was accounted for in the PCA. No diversity was observed among basidiospore isolates that were recovered from single basidiocarps, reflecting the pathogen¿s homomictic (primary homothallic) reproduction. A difference at a single locus distinguished mass isolates from a broom from Bolivia, indicating that brooms may be infected with more than a single individual. The results corroborate those of previous RAPD studies that concluded that two different populations of the pathogen exist in the Bahia State of Brazil. The present results suggest that these populations may have been introduced from the States of Para and Rondonia in Brazil.