Formation of Erysiphe necator Chasmothecia in the Pacific Northwest United States

Authors: THIESSEN, LINDSEY - North Carolina State University; Neill, Tara; Mahaffee, Walter - Walt

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2018
Publication Date: 2/25/2019
Citation: Thiessen, L.D., Neill, T.M., Mahaffee, W.F. 2019. Formation of Erysiphe necator Chasmothecia in the Pacific Northwest United States. Plant Disease. 103(5):890-896. https://doi.org/10.1094/PDIS-06-18-1012-RE.
DOI: https://doi.org/10.1094/PDIS-06-18-1012-RE

Interpretive Summary: In the Pacific Northwest, chasmothecia formation is not observed in vineyards until the beginning of véraison despite heavy infestations whereby 100% of leaf tissue is covered by Erysiphe necator. Mating type proximity and distribution were sampled from individual lesions (~70.9 mm2) on leaf tissue in a stratified sampling from three canopy heights at three times during the 2013, 2014 and 2015 growing seasons. Both mating types were observed at every sampling point and within the same lesions at all sampling dates and canopy heights. Effect of temperature and day length were examined by inoculating seedlings with known mating type 1 and 2 isolates and placed in incubators at different temperatures (5, 10, 15, 20, 25, and 30°C) or different day length changes (long day to long day, long day to short day, short day to short day, and short day to long day). Chasmothecia were produced at all temperatures that E. necator was able to colonize tissue, and the greatest number of chasmothecia were produced at 15 and 20°C (P = 0.02). Day length shifts from short day (8 hours) to long day (16 hours) resulted in a significant increase in chasmothecia production (P < 0.001). End of season plant stress observed in the Pacific Northwest, such as water-stress or host senescence, was assessed under naturally-infested field conditions by either girdling canes or applying 150 mg·l-1 abscisic acid solution to vines, respectively and quantifying chasmothecia production. No differences were observed in chasmothecia production in the plant stress assessment, likely due to the high vigor and ability for plants to overcome stress treatments.

Technical Abstract: In the Pacific Northwest, formation of the overwintering fungal structure (chasmothecia) is not observed in vineyards until the beginning of véraison despite heavy infestations whereby 100% of leaf tissue is covered by Erysiphe necator. This research investigated factors that influenced chasmothecia formation in an effort to better understand when the subsequent spring epidemic is likely to be initiated. Results indicate the formation of the overwintering inoculum is dependent on factors other than those examine but is not due to just proximity of mating types currently accepted in the literature.