A Comparison of Immediate and Short-Term Defensive Responses to Phytophthora Species Infection in Both Susceptible and Resistant Walnut Rootstocks

Clonal rootstocks are one alternative used by the walnut industry to control damage caused by species, traditionally using plants grafted on susceptible rootstock. Vlach, VX211, and RX1 are clonal rootstocks with a degree of resistance to species. The resistance to pathogens in these rootstocks depends on the resistance mechanisms activated by the presence of the pathogen and subsequent development of responses in the host. In this work, we analyzed how plants of , Vlach, VX211, and RX1 responded to inoculation with or isolates obtained from diseased English walnut plants from Chilean orchards. After inoculation, plants of Vlach, VX211, and RX1 showed canopy and root damage indexes that did not differ from noninoculated control plants. In contrast, plants of , which is susceptible to and , died after inoculation. Vlach, VX211, and RX1 plants inoculated with or showed greater root weight and volume and greater root growth rates than their respective controls. These results suggest that short-term carbohydrate dynamics may be related to the defense mechanisms of plants; they are immediately activated after inoculation through the production of phenolic compounds, which support the further growth and development of roots in walnut clonal rootstocks. To our knowledge, this is the first study that comprehensively characterizes vegetative and radicular growth and the dynamics of sugars and phenols in response to infection with or in walnut rootstocks.