Submitted to: International Journal of Fruit Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2013
Publication Date: 6/4/2013
Citation: Gigot, J., Walters, T., Zasada, I.A. 2013. Impact and occurrence of Phytophthora rubi and Pratylenchus penetrans in commercial red raspberry (Rubus idaeus) fields in northwestern Washington. International Journal of Fruit Science. 13:357-372. Interpretive Summary: Soilborne pathogens, including microscopic plant-parasitic nematodes and the water mold Phytophthora, cause significant loss in yield to raspberry annually. Raspberry farmers lack effective and long-term ways of reducing numbers of these organisms in production fields. This research was conducted to determine the distribution of these pathogens in raspberries grown in Washington state, to understand environmental factors that may relate to the occurrence of the pathogens, and to better understand the effect of these pathogens on raspberry productivity. Soil and root samples were collected from raspberry farmer fields and numbers and occurrence of soilborne pathogens were determined. Both soilborne pathogens were found in all sampled fields; however, numbers and occurrence varied between locations. In controlled experiments, it was discovered that the water mold was very harmful to raspberry, and disease severity increased with numbers of the pathogen. Combined, the soilborne pathogens did not increase the severity of disease. These results are significant because they document the widespread occurrence of these soilborne pathogens in raspberry and demonstrate that disease severity is related to initial numbers of Phytophthora. This research will be used by scientists and farms to manage plant-parasitic nematodes and Phytophthora in commercial raspberry fields.
Technical Abstract: Red raspberry (Rubus idaeus) production is a vital component of northwestern Washington’s agriculture. The main objectives of this study were to document the occurrence of soilborne pathogens Phytophthora rubi and Pratylenchus penetrans in early stage production fields, relate this information to soil properties, and better understand the individual and combined effect of P. rubi and P. penetrans on raspberry root health. P. rubi was found at each field and P. penetrans population densities were variable (0 to ~8,000 nematodes/g dry root) across locations. In controlled greenhouse studies, P. rubi was very pathogenic to red raspberry ‘Meeker’ at densities > 10 oospore/gram soil and there was no interaction between P. rubi and P. penetrans. P. rubi is endemic to raspberry production in this region, and is an aggressive pathogen on raspberry. However, the chronic damage to roots caused by P. penetrans should not be ignored.