Nuclear DNA content of the hybrid plant pathogen Phytophthora andina determined by flow cytometry

Abstract

Phytophthora andina is a heterothallic plant pathogen of Andean solanaceous hosts and is an interspecific hybrid of P. infestans and an unknown Phytophthora species. The objective of this study was to estimate the nuclear DNA content of isolates in three clonal lineages of P. andina relative to P. infestans. Twelve isolates of P. andina and six isolates of P. infestans were measured for nuclear DNA content by propidium iodide-stained flow cytometry. We found that the DNA content of P. andina was similar but slightly smaller, on average, than that of our sample of P. infestans isolates. This is consistent with P. andina being a homoploid hybrid rather than allopolyploid hybrid. Nuclear DNA content was more variable among a smaller sample of P. infestans isolates, including a putative triploid isolate from Mexico, but small differences in nuclear DNA content were also observed among P. andina isolates. Both species appear to be able to tolerate significant variation in genome size.

• flow cytometry
• interspecific hybrid
• Phytophthora infestans
• ploidy

Acknowledgments

We thank Gregory Forbes, Ricardo Oliva, Sylvia Fernândez-Pavía, and Niklaus Grünwald for sharing isolates, Claude Husson for advice on preparing Phytophthora nuclei for flow cytometry, Neal Benson and the UF ICBR cytometry core lab for training and support and anonymous reviewers for comments that improved this manuscript. This research was supported by the University of Florida Emerging Pathogens Institute and the Institute of Food and Agricultural Sciences Department of Plant Pathology.