Field and Greenhouse Response of Red Raspberry Genotypes to Root Rot

Abstract

Red raspberry genotypes (Rubus idaeus L.) were evaluated for resistance to root rot at two field sites in Washington state and in a greenhouse study. Thirteen raspberry genotypes were planted in two field sites naturally infested with Phytophthora fragariae var. rubi Wilcox and Duncan and evaluated over 3 years for growth and symptom expression. In greenhouse pot tests, 14 genotypes were inoculated with an isolate of P. fragariae var. rubi at three inoculum levels and evaluated for growth, root color, and symptom expression using a 1 to 4 rating scale. Eleven of the 14 cultivars were found to be susceptible or very susceptible to root rot in the field and greenhouse. ‘Summit’ and ‘Newburgh’ possessed high levels of resistance to the pathogen. ‘Cascade Bounty’ also showed high resistance to root rot in the greenhouse, but confirmation from a field study is needed. Subjective root ratings of greenhouse-grown plants correlated well with measurements of cane numbers and cane infection in the field. The greenhouse tests were useful in identifying resistant genotypes and very susceptible genotypes but did not always match field results. Observation of at least 3 years in the field was necessary to compare relative reaction with root rot among genotypes.