Identification of Environmental Factors Related to Claviceps purpurea Ascospore Production in Perennial Ryegrass Seed Fields and Development of Predictive Models

Abstract

Claviceps purpurea, the causal agent of ergot of perennial ryegrass seed crops, overwinters as sclerotia in the soil and releases airborne ascospores in the spring that infect flower ovaries and replace seed with sclerotia. Burkard spore traps were used to quantify the dispersal phenology and concentration of ascospores in perennial ryegrass seed fields in the Columbia Basin of Oregon. Weather factors were measured concurrently with spore trapping. Nonparametric regression, box-and-whisker plots, and univariate analysis were used to visualize and identify trends between ascospore concentrations and weather variables. Most ascospores (75.4%) were trapped when minimum soil temperatures were between 16.2 and 20.4°C. Over 67% of the total ascospores trapped were observed when minimum air temperatures were between 6.8 and 12.4°C and 64% of ascospores were trapped when daily mean dew point was between 3.7 and 8.2°C. Environmental favorability index (EFI) models were developed and validated based on their ability to predict ascospore occurrence. The EFI models were able to predict ascospore occurrence with an accuracy of 71.7 to 87.5% depending on the year. The models were up to 79.8% accurate when validated using three years of historical spore trap data not used in the EFI model development. Ninety-four percent of ascospores were trapped when cumulative air degree days, using lower and upper thresholds of 10 and 25°C, respectively, were between 230 and 403. These results suggest that weather parameters can be used to model C. purpurea ascospore occurrence and potentially improve the timing and efficacy of fungicide applications by identifying when plant protection is most needed.

Has Selection for Grain Yield Altered Intermediate Wheatgrass?

“…While the mean for ergot occurrence was higher in 2014 (Table 1), the highest individual value was found in 2013, where nearly all recovered material was ergot (95%). Precipitation was higher and temperatures cooler in 2014, most likely enhancing the disease [44].…”

Ergot in Pacific Northwest Grass Seed Crops

“…Air and soil temperatures in the spring can affect the timing, duration, and quantity of capitula production during host anthesis (Markhasseva, 1936). Research in the lower Columbia Basin of Oregon revealed that most ascospores were observed when minimum soil temperatures were between 61.2 and 68.7°F and maximum soil temperatures were between 67.3 and 79.0°F (Dung et al., 2017). Air temperature, which is often easier to measure than soil temperature, was also strongly correlated with ascospore production events.…”

“…A degree‐day model that predicted ergot ascospore presence in the lower Columbia Basin of Oregon was developed using such data from perennial ryegrass seed crops in the lower Columbia Basin of Oregon (Dung et al., 2017). On average, the degree‐day model accounted for 93% of ascospores produced during the grass seed production season in the region.…”

Complete Issue

“…Air and soil temperatures in the spring can affect the timing, duration, and quantity of capitula production during host anthesis (Markhasseva, 1936). Research in the lower Columbia Basin of Oregon revealed that most ascospores were observed when minimum soil temperatures were between 61.2 and 68.7°F and maximum soil temperatures were between 67.3 and 79.0°F (Dung et al, 2017). Air temperature, which is often easier to measure than soil temperature, was also strongly correlated with ascospore production events.…”

“…A degree-day model that predicted ergot ascospore presence in the lower Columbia Basin of Oregon was developed using such data from perennial ryegrass seed crops in the lower Columbia Basin of Oregon (Dung et al, 2017). On average, the degree-day model accounted for 93% of ascospores produced during the grass seed production season in the region.…”