Our lab is studying the population biology of the grape powdery mildew fungus, Erysiphe necator (syn. Uncinula necator). Research is focused on genotypic and phenotypic variation of E. necator in the eastern US, where this fungus is native. Our initial efforts have used multilocus sequencing based on three gene regions. These data have been analyzed in a phylogeographic context in comparison to introduced populations in the western US, Europe and Australia. To complement molecular population genetics, we are studying variation in pathogenicity and aggressiveness, particularly in populations sampled from wild Vitis species in the eastern US. With samples from several different species we are exploring whether the extent of host specialization in E. necator. As part of a transcriptome sequencing project in collaboration with Dr. Lance Cadle-Davidson at the USDA-ARS Grape Genetics Research Unit in Geneva, NY, we are developing additional molecular markers for more in-depth population genetic analyses. These new markers include microsatellites (or SSRs), single-nucleotide polymorphisms (SNPs), and a PCR-based marker for mating type. Finally, we are collaborating with Dr. Wayne Wilcox, Dept. of Plant Pathology and Plant-Microbe Biology, Cornell University, Geneva, NY on correlating gene expression with resistance to demethylation-inhibiting fungicides (DMIs).
Current and recent projects on E. necator:
- Phylogeography of native and introduced populations
- Variation in pathogenicity and aggressiveness
- Transcriptome sequencing and marker development
- Mating-type genes in E. necator and other powdery mildews
- Population structure in the eastern US assessed by microsatellites
- Gene expression correlated to DMI resistance
The main activity of our lab from the early 1990s until 2005 was to understand the genetic and biological constraints on biological control of chestnut blight, in a phenomenon known as hypovirulence. Some viruses found in C. parasitica have been responsible for the biological control and almost complete recovery of chestnut trees from blight in southern Europe and a few places in North America. Our research has addressed questions about the spread of viruses—or the lack of spread in the U.S.—for biological control. We conducted extensive research in three main areas relating to this question:
1) Genetics and population genetics of vegetative incompatibility, which restricts the transmission of viruses from one fungal individual to another;
2) The mating system of C. parasitica, because recombination generates greater diversity of vegetative compatibility types, and hence restricts virus spread. We have studied the mating system both in the field and in laboratory, e.g., cloning mating-type genes;
3) Transmission and population genetics of the viruses responsible for hypovirulence.
- Cloning of vegetative incompatibility genes;
- The formation of mating-type heterokaryons in clonal populations of C. parasitica;
- Genome sequencing of C. parasitica.
Aflatoxins are among the most carcinogenic compounds known and contaminate a variety of grains and nuts, particularly in the tropics. They are produced by Aspergillus species, particularly A. flavus and A. parasiticus. We have recently begun a project to study the determinants of aflatoxin accumulation in maize in east Africa. Factors we are focusing on include: stresses during the growing season (e.g., drought, pests, etc.), cultivar resistance to A. flavus, drying techniques before storage, and post-harvest storage conditions. This project is being done in collaboration with researchers in plant breeding, agronomy and applied economics.