Phylogeny of Pseudocercospora griseola from Puerto Rico, Central America and Tanzania confirms the existence of an Afro-Andean clade

Authors: SERRATO-DIAZ, LUZ - University Of Puerto Rico; NAVARRO-MONSERRAT, E. - University Of Puerto Rico; ROSAS, J. - Zamorano, Panamerican School Of Agriculture; CHILAGANE, L. - Sokoine University Of Agriculture; BAYMAN-GUPTA, P. - University Of Puerto Rico; Porch, Timothy - Tim

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2020
Publication Date: 5/29/2020
Citation: Serrato-Diaz, L.M., Navarro-Monserrat, E.D., Rosas, J.C., Chilagane, L.A., Bayman-Gupta, P., Porch, T.G. 2020. Phylogeny of Pseudocercospora griseola from Puerto Rico, Central America and Tanzania confirms the existence of an Afro-Andean clade. European Journal of Plant Pathology. 157:533-547. https://doi.org/10.1007/s10658-020-02015-8.
DOI: https://doi.org/10.1007/s10658-020-02015-8

Interpretive Summary: Angular Leaf Spot (ALS) is an important fungal disease of common bean. Previous studies have demonstrated that ALS and bean have co-evolved, resulting in the classification of the fungus into Middle American and Andean groups that reflect the evolutionary history of the host. However, an unusual group of ALS isolates found in Africa, termed Afro-Andean, was previously found to be pathogenic on Middle American cultivars. This study evaluated the diversity of ALS isolates from four countries and confirms the existence of an Afro-Andean clade. A total of 171 ALS isolates from Puerto Rico, Honduras, Guatemala and Tanzania were evaluated. Four nuclear genes were sequenced and used to construct a phylogenetic tree to look at evolutionary history. Phylogenetic inference grouped all isolates from Puerto Rico, Honduras and Guatemala in the Middle American clade. For Tanzanian isolates, 34 were Middle American and 40 Andean, and a third population was discovered with 12 hybrid isolates. This unusual group of 12 isolates from Tanzania were subsequently confirmed to be a separate Afro-Andean clade. These molecular findings provide definitive proof to previous findings indicating the existence of a novel Afro-Andean clade. Isolation with migration models showed that the divergence between Middle American and Andean P. griseola populations occurred approx. 100,000 years ago, and that the Afro-Andean clade is a sister clade of the Andean population that diverged approx. 40,000 years ago. These results are important in understanding the co-evolution of beans and pathogens, and for informing current and future bean breeding efforts.

Technical Abstract: Angular Leaf Spot (ALS), caused by the fungus Pseudocercospora griseola, is an important disease of common bean (Phaseolus vulgaris L.). Previous studies have demonstrated that P. griseola and Phaseolus vulgaris have co-evolved, resulting in the classification of the fungus into Middle American and Andean groups that reflect the evolutionary history of the host. However, an unusual group of ALS isolates found in Africa, termed Afro-Andean, was previously found to be pathogenic on Middle American cultivars. This study evaluated the diversity of P. griseola isolates from four countries and confirms the existence of an Afro-Andean clade. A total of 171 ALS isolates from Puerto Rico, Honduras, Guatemala and Tanzania were evaluated. Four nuclear genes (ß-tubulin, actin, the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA, and the nuclear small subunit rRNA gene) were sequenced and used to construct a phylogenetic tree using a coalescence model. Phylogenetic inference grouped all isolates from Puerto Rico, Honduras and Guatemala in the Middle American clade. For Tanzanian isolates, 34 were Middle American and 40 Andean, and a third population was discovered with 12 hybrid isolates. This unusual group of 12 isolates from Tanzania were subsequently confirmed to be a separate Afro-Andean clade. These molecular findings provide definitive proof to previous findings indicating the existence of a novel Afro-Andean clade. Isolation with migration models showed that the divergence between Middle American and Andean P. griseola populations occurred approx. 100,000 years ago, and that the Afro-Andean clade is a sister clade of the Andean population that diverged approx. 40,000 years ago. These results are important in understanding the co-evolution of beans and pathogens, and for informing current and future bean breeding efforts.