Development of optimized Verticillium longisporum inoculation techniques for canola (Brassica napus)

Abstract Verticillium stripe, caused by Verticillium longisporum, is an emerging soilborne disease of canola (Brassica napus) in Canada. Improved inoculation protocols will facilitate study of Verticillium stripe and its management. Two inoculation techniques, a root-dip method at two inoculum concentrations and a grain inoculation method at four inoculum concentrations, were compared under greenhouse conditions with the canola cultivars ‘45H31’, ‘CS2000’ and ‘Westar’. Symptoms of Verticillium stripe appeared at early growth stages following root dip inoculation, resulting in seedling mortalities of up to 19.7%, 39.5% and 33.3% for ‘CS2000’, ‘45H31’ and ‘Westar’, respectively, at 35 days post-inoculation. Plants inoculated by the root-dip method incurred much greater mortality at the high versus low inoculum concentration. In the surviving adult plants, ‘45H31’ was moderately resistant while ‘CS2000’ was more susceptible to V. longisporum. The grain inoculation method did not cause early-stage mortality, although Verticillium stripe severity at the adult stage was significantly different between control and high inoculum concentrations for all cultivars. In addition, plant dry weight and height decreased as inoculum concentration increased. Inoculation of 1-week-old, 2-week-old and 3-week-old seedlings of ‘CS2000’ and ‘Westar’ was also compared by the root-dip method. The impact of host age at inoculation on disease development was not significant, although higher disease severity was observed at later inoculation in ‘CS2000’. The application of grain inoculum may be more suitable for large-scale screening or studies conducted under field conditions.