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Temporal dispersal patterns of Sclerotinia sclerotiorum ascospores during canola flowering

Qandah, Issa S., del Río Mendoza, L. E.
Canadian journal of plant pathology 2011 v.33 no.2 pp. 159-167
Sclerotinia sclerotiorum, air temperature, ascospores, canola, canopy, flowering, relative humidity, samplers, soil temperature, soil water, temporal variation, North Dakota
The temporal patterns of Sclerotinia sclerotiorum ascospore dispersal in canola fields were studied at two North Dakota locations between 2005 and 2007. Seven-day volumetric spore samplers were used to monitor airborne ascospore populations while electronic data loggers recorded hourly information on air temperature, relative humidity, soil moisture and soil temperature under the canola canopy. Ascospore dispersal occurred during single periods that lasted 4 to 6 hours. In 2005 and 2007, most ascospores were collected between 10 am and 1 pm; however, in 2006, a drier than normal year, most were collected between 2 am and 7 am. In 2005 and 2007, the first sharp increase in ascospore dispersal was preceded by a 10-unit drop in relative humidity from close to saturation, and an increase in air temperature of 5 °C. In 2006, however, no significant changes in relative humidity, which remained around 90%, or air temperature, which hovered around 15 °C, were recorded prior to the start of the discharges. These nighttime discharges lasted 2 hours longer than daytime discharges. Daily discharges, daytime and nighttime, started when relative humidity was ≥ 90% and air temperature was around 15–16 °C. Multiple peak-days, days with mean ≥ 20 ascospores m⁻³, were recorded in 2005 and 2007, but none were recorded in 2006. Peak-days were associated with preceding periods of seven consecutive days with mean relative humidity ≥ 85% in the canola canopy.