Methods for assessing the resistance of raspberry genotypes to <i>Phytophthora</i> root rot

Abstract

Zoospores and agar discs of the fungus causing raspberry root rot (Phytophthora fragariae) were used as inoculum to assess the resistance of raspberry genotypes in pot experiments. High zoospore concentrations resulted in more severe symptoms than low concentrations. There was a strong correlation between the results obtained with zoospores and with colonized agar discs as inocula. although disease was generally more severe with the former. The severity of root rot was correlated with a number of other symptoms, in particular growth reductions, stem lesions and leaf wilting, and some of these symptoms could possibly be used as measures of resistance. There was no evidence of physiological specialization with the range of isolates and raspberry genotypes used. Pot tests in general gave results which matched reported resistances in the field, and could be used to assess the resistance of breeding lines and selections.