|WALENTA, D - Oregon State University|
|HAMM, P - Oregon State University|
|DUNG, J - Oregon State University|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2015
Publication Date: 8/14/2015
Citation: Alderman, S.C., Walenta, D.L., Hamm, P.B., Martin, R.C., Dung, J. 2015. Afternoon ascospore release in Claviceps purpurea optimizes perennial ryegrass infection. Plant Disease. doi: 10.1094/PDIS-09-14-0978-RE.
Interpretive Summary: In spore trapping studies of Claviceps purpurea in perennial ryegrass, the time of day of spore release (afternoon) was found to differ from early morning spore release in other grasses such as Kentucky bluegrass. The afternoon spore release was also observed under controlled laboratory conditions. Molecular analyses suggest this may be a unique strain of C. purpurea. Afternoon spore release coincides with the optimum time of day for infection in perennial ryegrass and this may have implications for timing of fungicide applications.
Technical Abstract: In Kentucky bluegrass, Claviceps purpurea, the causal agent of ergot, typically releases ascospores during the early morning hours, between about midnight and 10:00 a.m., corresponding to time of flowering, when the unfertilized ovaries are most susceptible for infection. During aeromycology studies of C. purpurea in perennial ryegrass in northeastern Oregon during 2008-2010 and 2013, a strain of C. purpurea was found that released ascospores in the afternoon, coinciding with flowering in perennial ryegrass. Under controlled environmental conditions, sclerotia from perennial ryegrass and Kentucky bluegrass released spores in the afternoon and morning, respectively, consistent with timing of spore release under field conditions. Internal transcribed spacer (ITS) sequences of single sclerotial isolates from Kentucky bluegrass and perennial ryegrass were consistent with C. purpurea, although minor variations in ITS sequences among isolates was noted. Differences between Kentucky bluegrass and perennial ryegrass isolates were observed in random amplified polymorphic DNA (RAPDs). Evidence is provided for adaptation of Claviceps purpurea to perennial ryegrass by means of delayed spore release that coincides with afternoon flowering in perennial ryegrass.