Pulse Industry

Project Abstract: Controlling White Mould Disease through Microclimate Management

Dry bean (Phaseolus vulgaris L.) is the most profitable pulse crop grown under irrigation in southern Alberta. White mold (WM) caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bary is a major constraint to dry bean production.

Due to the absence of any complete genetic resistance to this pathogen, microclimate within the canopy and prevailing environmental conditions are the most important determinants of white mould progression. Therefore, the proposed research would aim to determine whether microclimate management, provided by changes in irrigation scheduling and dry bean canopy architecture, could decrease the rate of ascospore release during the susceptible flowering period, without negatively affecting bean yield.

Field studies were conducted at AAFC-Lethbridge in 2014, 2015 and 2016 to determine the effect of irrigation and plant architecture on canopy microclimate, white mold disease development and yield. Three levels of irrigation (high, medium and low) and five cultivars  with different canopy architecture (semi-upright bush, upright bush and prostrate) were arranged  in a split-plot design and plots were evaluated for WM incidence and severity, flower infection, yield and thousand seed weight (TSW). Microclimate variables, such as soil water content, leaf wetness, soil temperature, and canopy porosity were monitored using data loggers and sensors.

Statistical analysis indicated that there were significant interactions between cultivars, microclimate and WM. In all 3 years, WM incidence, severity and flower infection were significantly higher in high irrigation plots compared to medium and low irrigation plots. However, plots grown under medium and low irrigation had similar WM levels, but yield and TSW were reduced under low irrigation. Higher water content within the top 5-cm of soil, prolonged leaf wetness and cooler canopy temperatures were maintained in high irrigation plots compared to medium and low irrigation plots. Soil temperatures favourable to apothecia development and ascospore release were only maintained in high irrigation plots. 

In all 3 years, WM development in AAC Burdett and I9365-31, lines with partial field and genetic resistance, respectively, were not affected by irrigation regime. In 2016, ascospore release was also monitored using Burkard 7-day spore samplers, and quantification of airborne inoculum using real-time PCR with S. sclerotiorum specific primers and TaqMan probe, but data analysis and interpretation is ongoing. This trial will be conducted for 1 more year and data from all 4 years will be combined and analyzed.

A preliminary WM prediction model was developed by correlating WM severity with microclimate data. Pearson’s correlation coefficient revealed significant relationship of WM severity with soil moisture, leaf wetness and soil temperature. Lodging was positively correlated with WM severity while the relationship was negative for canopy porosity. Flower infection was highly correlated with WM severity and explained maximum variability.

Results from the trials indicate that irrigation schedule and choice of cultivars can be effective tools for WM management in Alberta.

Project lead: Dr. Syama Chatterton   (403) 317-2226   syama.chatterton@agr.gc.ca 
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