Dr. Amos Dinoor - Department of Plant Pathology and Microbiology. 

A method for estimating disease induced yield losses by using single wheat tillers as experimental units was evaluated under commercial field conditions. Natural epidemics of Septoria tritici blotch, yellow rust and leaf rust which developed late in the season had no effect on the vegetative growth of the host, but caused only reduced kernels weight. The optimal sample size was determined experimentally to be 300 tillers. Losses were also estimated in the same experiments using field plots as experimental units. Yield loss estimates derved from using single tillers were significantly correlated with those derived from using field plots. The relationship between disease and yield varied significantly among fields, even in a given year, region and cultivar. Thus, it was concluded that this relationship has to be established empirically wherever yield losses are to be estimated, and that under Israeli conditions it may be done by using the single tillers method.