Evaluation of Spray and Point Inoculation Methods for the Phenotyping of Puccinia striiformis on Wheat

The fungus Puccinia striiformis causes yellow (stripe) rust on wheat worldwide. In the present article, new methods utilizing an engineered fluid (Novec 7100) as a carrier of urediniospores were compared with commonly used inoculation methods. In general, Novec 7100 facilitated a faster and more flexible application procedure for spray inoculation and it gave highly reproducible results for virulence phenotyping. Six point inoculation methods were compared to find the most suitable for assessment of pathogen aggressiveness. The use of Novec 7100 and dry dilution with Lycopodium spores gave an inoculation success rate of 100% in two independent trials, which was significantly higher and more consistent than for spore suspension in Soltrol 170, water, water + Tween 20, and Noble agar + Tween 20. Both Soltrol 170 and Novec 7100 allowed precise quantification of inoculum, which is important for the assessment of quantitative epidemiological parameters. New protocols for spray and point inoculation of P. striiformis on wheat are presented, along with the prospect for applying these in rust research and resistance breeding activities.