Submitted to: Journal of Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2007
Publication Date: 9/10/2007
Citation: Albrecht, U., Bowman, K.D. 2007. Inducible proteins in citrus rootstocks with different tolerance towards the root rot pathogen Phytophthora palmivora. Journal of Phytopathology. 155:606-615. Interpretive Summary: Fungal diseases caused by Phytophthora can be very damaging to the roots and trunks of citrus trees like orange, grapefruit, and mandarin. Previous research with other plants has identified particular proteins that are often associated with defenses of the plant to disease infection. The relative amounts of some of these defense-related proteins may provide a measure of the relative resistance of a plant to disease. In this study, the particular proteins examined did not appear directly associated with the primary defenses of citrus trees to infection by Phytophthora disease. However, some of these proteins appeared to be involved in moderating the severity of disease development after infection occurs.
Technical Abstract: Activities of defense-related proteins (ß-1,3-glucanases, chitinases and peroxidases) and concentrations of total soluble phenolics were measured in roots and leaves of uninfected and infected plants to investigate the response of different citrus rootstock genotypes to the root rot pathogen Phytophthora palmivora (Butler). Infection with the pathogen increased concentrations of total proteins, total phenolics and ß-1,3-glucanase activity in roots of all genotypes, and increases were associated with the extent of root mass reductions and thus susceptibility of the plants. Root chitinase and root peroxidase levels were slightly reduced or unaltered upon infection. ß-1,3-Glucanase activity was also elevated in leaves of infected plants, but increases did not differ between tolerant and susceptible rootstocks. Effects of root infection on leaves were typically the reverse of effects on roots for total protein-, chitinase- and peroxidase levels. In both tissues effects were most pronounced in susceptible rootstock genotypes. Although differences in enzyme expression were observed between susceptible and tolerant citrus seedlings, effects were usually associated with disease progression, and not with resistance to P. palmivora. The results of this study suggest that increased activities of defense-related proteins and soluble phenolics are not implicated in the primary defense to phytophthora root diseases, but may contribute to the inhibition of the pathogen during infection in tolerant citrus.