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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #343536
Title: Identification of environmental factors related to Claviceps purpurea ascospore production in perennial ryegrass seed fields and development of predictive models

Author
item DUNG, JEREMIAH - Oregon State University
item Alderman, Stephen
item KAUR, NAVNETT - Oregon State University
item WALENTA, DARRIN - Oregon State University
item FROST, KENNETH - Oregon State University
item HAMM, PHILIP - Oregon State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2017
Publication Date: 7/17/2017
Citation: Dung, J.K., Alderman, S.C., Kaur, N., Walenta, D.L., Frost, K.E., Hamm, P.B. 2017. Identification of environmental factors related to Claviceps purpurea ascospore production in perennial ryegrass seed fields and development of predictive models. Plant Disease. 101:895-906.

Interpretive Summary: Claviceps purpurea is a fungus that causes the disease ergot in perennial ryegrass seed crops. The fungus overwinters as hard dark resting bodies called sclerotia in the soil and releases airborne spores in the spring that infect flowers and replaces the seed with new sclerotia. Traps to collect spore were used to quantify the dispersal timing and concentration in perennial ryegrass seed fields in the Columbia Basin of Oregon. Weather factors were measured concurrently with spore trapping. Most spores (75.4%) were trapped when minimum soil temperatures were between 16.2 and 20.4°C. Over 67% of the total spores trapped were observed when minimum air temperatures were between 6.8 and 12.4°C and 64% of spores were trapped when daily mean dew point was between 3.7 and 8.2°C. Models that describe the environmental favorability were developed and determined to have the ability to predict the occurrence of spore release. The models were up to 79.8% accurate when validated using three years of historical spore trap data. These results suggest that weather parameters can be used to model C. purpurea spore occurrence and potentially improve the timing and efficacy of fungicide applications by identifying when plant protection is most needed.

Technical 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.