Genome size variation in the pine fusiform rust pathogen Cronartium quercuum f.sp. fusiforme as determined by flow cytometry

Abstract

The genome size of the pine fusiform rust pathogen Cronartium quercuum f.sp. fusiforme (Cqf) was determined by flow cytometric analysis of propidium iodide-stained, intact haploid pycniospores with haploid spores of two genetically well characterized fungal species, Sclerotinia sclerotiorum and Puccinia graminis f.sp. tritici, as size standards. The Cqf haploid genome was estimated at ~90 Mb, similar to other Pucciniales species for which reference genome sequences are available. Twenty-three Cqf pycniospore samples were compared that comprised three samples obtained from naturally occurring pine galls and 20 samples obtained after artificial inoculation with parental isolates and their progeny. Significant variation in genome size (>10% of mean) was detected among unrelated as well as sibling Cqf samples. The unexpected plasticity in Cqf genome size observed among sibling samples is likely to be driven by meiosis between parental genomes that differ in size.

• Cronartium quercuum f.sp. fusiforme
• flow cytometry
• fusiform rust disease
• genome size
• propidium iodide
• pycniospore
• spermatia

The authors gratefully acknowledge the contributions of Tania Quesada (School of Forest Resources and Conservation, University of Florida), Charles Barnes and Les Szabo (USDA ARS Cereal Disease Laboratory, University of Minnesota) and Jeffrey Rollins (Department of Plant Pathology, University of Florida) for providing fungal material, without which this project could not have been completed. We also thank Katherine Smith (USDA-Forest Service, School of Forest Resources and Conservation, University of Florida) for excellent technical assistance, Neal Benson (Interdisciplinary Center for Biotechnology Research Flow Cytometry Core Lab (ICBR-FCCL), University of Florida) for providing advice and assistance with flow cytometry and Steve McLellan (ICBR-FCCL, University of Florida) for providing confocal fluorescence microscopy services. The ICBR-FCCL is financially supported by an equipment grant from the Bankhead-Coley Cancer Research Program. This research was supported in part by Cooperative Agreement 09-CA-11330126-058 between the USDA-Forest Service Southern Research Station (Southern Institute of Forest Genetics) and the University of Florida.