|RODRIGUEZ-SALAMANCA, LINA - Iowa State University|
|QUESADA-OCAMPO, LINA - North Carolina State University|
|HAUSBECK, MARY - Michigan State University|
Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2018
Publication Date: 3/20/2018
Citation: Rodriguez-Salamanca, L., Naegele, R.P., Quesada-Ocampo, L.M., Hausbeck, M.K. 2018. Inoculation method, temperature and relative humidity affects leaf and neck anthracnose, a new onion disease in Michigan. Plant Health Progress. 19(1):64-68. https://doi.org/10.1094/PHP-10-17-0063-RS.
Interpretive Summary: A new disease of onion was identified in Michigan caused by the plant pathogen Colletotrichum coccodes. Inoculation methods, humidity, and temperature requirements for disease were compared on onion seedlings grown in the greenhouse. Of the two inocula tested, conidial suspensions had higher disease severity than infested millet seed. Extended periods (24 hours) of high relative humidity (95%) and temperature (25ºC) were found to increase disease severity. Results from this study suggest that onion leaf and neck anthracnose symptoms are likely to be more severe under warm and humid environmental conditions.
Technical Abstract: Leaf and neck anthracnose caused by Colletotrichum coccodes is a new disease of onion in Michigan. To test the effect of inoculation method, ‘Prince’ onion seedlings were grown in the greenhouse and inoculated with either a conidial suspension of C. coccodes (alone or with an abrasive agent) or infested millet seed (dry or wet, 2 or 5 g). Final foliar disease severity was greater when a conidial suspension (>39%) was used compared to infested millet seed (24.3%). Growth chamber studies were conducted using ‘Infinity’ onion seedlings that were inoculated with a conidial suspension spray to determine the effects of temperature (15, 20, 25 or 30°C) and duration (0, 12, 24, 48 or 72 h) of high (95 ± 5%) relative humidity (RH) on disease severity (percentage of leaf area with C. coccodes lesions). Significant differences and interactions among temperature and RH were observed. The combination of high temperature (25°C) and extended (24 h) high RH resulted in >20% disease severity 28 days post inoculation. Results suggest that onion leaf and neck anthracnose symptoms are likely to be more severe when the environmental conditions are 25ºC with 24 h of high RH.