Abstract Detail

Poster Session

Stewart, Jane [1], Brewer, Marin [1].

Drivers of divergence and host range expansion in a fungal species complex pathogenic to cucurbits and papaya.

Host specialization and host-plant domestication are factors that can drive speciation in plant-pathogenic fungal taxa. Using a multilocus sequencing approach of 55 isolates, we have discovered that Didymella bryoniae, a pathogen of cucurbits, is composed of three genetic lineages (L1, L2, L3). Unexpectedly, one of the lineages (L3) is genetically and morphologically indistinguishable from a pathogen of papaya, Phoma caricae-papayae. Current research is aimed at determining host specialization among lineages and inferring the ancestral host and divergence times of the lineages using coalescent analyses for four genome regions, internal transcribed spacer region (ITS), beta tubulin (BTUB), calmodulin (CAL), and chitin synthase I (CHS).  Pathogenicity assays showed that L3 is pathogenic to payapa (Carica papaya), whereas all three lineages are pathogenic to Cucurbita, Cucumis, and Citrullus species. A haplotype network of the combined dataset shows no reticulation among the distinct genetic lineages. Species tree estimates provide evidence for the existence of three distinct species, with L3 as the oldest species. Our time estimates for the divergence of L3 and L2 pre-date (70,000 years) domestication of Carica papaya and Cucurbitaceae, but it is possible that L3 host jumped on the newly arrived Cucurbitaceae gourds arriving by sea from Africa. The divergence estimate observed for L1 and L2 (10,900 years) suggests that domestication could have driven the divergence of these lineages as Cucurbita species moved northward out of South and Central America. This work highlights the use of molecular systematics and population genetics to elucidate genetic identity among previously unassociated fungi and to solve practical disease problems in the field.

1 - University of Georgia, Plant Pathology, 2309 Miller Plant Science Bldg, Athens, GA, 30602, USA

Keywords:
speciation
host specificity.

Presentation Type: Offered Paper - Poster
Session: P2
Location: Lincoln Room/Kellogg Hotel and Conference Center
Date: Tuesday, June 10th, 2014
Time: 8:00 PM
Number: P2007
Abstract ID:76
Candidate for Awards:None