We seek to determine the scope of fungicide resistance in Sclerotinia homoeocarpa populations in Pennsylvania and the surrounding region.

Specific Objectives: 1) Identify the scope of fungicide resistance to varying chemical classes in Pennsylvania; 2) track S. homoeocarpa population shifts throughout the growing season and; 3) examine the association between resistant fungal populations, various biological characteristics, and geographic distribution.

Fungicide Resistance. The goal of this study is to gain a better understanding of the scope of fungicide resistance to multiple chemical classes across Pennsylvania and the surrounding regions. After collecting hundreds of samples and isolating S. homoeocarpa from infected leaf tissue, we will subject the isolates to an in vitro fungicide assay. The fungicides used in this assay are boscalid, iprodione, thiophanate-methyl, and propiconazole. While resistance is known and documents in three out of four of these chemistries, we are interested in seeing where exactly resistance is present across PA and the surrounding regions. After screening the isolates to multiple concentrations across the four fungicides we will be able to have a better understanding of where fungicide resistance is occurring.

Seasonal Populations. Many superintendents across PA and surrounding states have expressed a growing concern over the difficulty they are having with controlling late-season or fall dollar spot. We experience a similar trend in our field fungicide trials at our research facility. In the fall, our nontreated control plots tend to recover from dollar spot damage naturally whereas the plots that have received multiple fungicide applications throughout the season and applications have stopped tend to drastically increase in dollar spot severity. It is unclear as to what exactly is causing this phenomenon. We are interested in the seasonality of dollar spot epidemics and what biological characteristics may be at play. We are tracking S. homoeocarpa populations and sampling throughout the growing season. These isolates will then be subjected to multiple studies, such as in vitro fungicides assays and vegetative compatibility group testing, in order to try and elucidate a relationship between seasonality and biological characteristics.

Biological Characteristics. Unique isolates, as it pertains to fungicide resistance, will be selected for further studies pertaining to vegetative compatibility and molecular characteristics. As we are interested in the scope of fungicide resistance across PA, we are also interested in the potential relationship resistant S. homoeocarpa populations may have with different vegetative compatibility groups. We are using VCG analysis to examine intra-species relationships across the broad range of isolates we have collected. These isolates will also be subjected to species level distinction at the molecular level in hopes to determine the genetic diversity of the pathogen populations.

Potential Impact. Dollar spot is the most economically important disease in the United States. Gaining a better understanding of the pathogen biology and population dynamics of S. homoeocarpa as they pertain to genetic factors such as genotype and phenotype variation and fungicide resistance is critical for managing dollar spot through a growing season. We hope to be able to connect these biologically different groups to specific dollar spot epidemics throughout the growing season and potential resistance development across multiple chemical classes.