Location: Horticultural Crops ResearchTitle: Root traits associated with Phytophthora root rot resistance in red raspberry Author
Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 1/17/2012
Publication Date: 4/30/2012
Citation: Valenzuela-Estrada, L.R., Bryla, D.R., Hoashi-Erhardt, W.K., Moore, P.P., Forge, T.A. 2012. Root traits associated with Phytophthora root rot resistance in red raspberry. Acta Horticulturae. 946:283-287. Interpretive Summary: Root rot is a common disease in raspberry in the northwestern United States. The disease is caused by a fungal-like soil organism called Phytophthora. Infected plants wilt rapidly under warm, dry conditions and often collapse and die. Raspberry cultivars vary in resistance to the disease, but the mechanism for resistance is unknown. The objectives of this study were to investigate root traits in red raspberry associated with increased resistance to root rot. The work is ongoing, but so far, it appears that root rot resistance may be related to both rapid root production and deposition of suberin in the roots, a waxy substance that inhibits Phytophthora infection. If this is the case, the traits could be selected during breeding to increase raspberry resistance to root rot.
Technical Abstract: Phytophthora root rot is a serious problem for commercial production of red raspberry. A study was initiated in 2009 to identify root traits in raspberry associated with little or no Phytophthora infection so that the traits can be selected and incorporated into breeding material to develop new cultivars with high resistance to root rot. The trial is located at the Washington State University Puyallup Research Center at a site with a long history of problems with the disease. The cultivars include ‘Summit’, which is highly resistant to root rot, ‘Cascade Bounty’ and ‘Cascade Delight’, also found to have high resistance, ‘Meeker’, the industry standard in the region with moderate resistance to root rot, ‘Tulameen’, which is similar to ‘Meeker’ in resistance, and ‘Malahat’ and ‘Saanich’, two cultivars highly susceptible to root rot. Our first year results indicate that cultivars with the highest resistance to root rot produced the most roots and the deepest root system. Resistant cultivars also had considerably less infection, according to qPCR analysis, by P. rubi, which is the species most often associated with root rot in raspberry. We began to examine the roots for evidence of suberin deposition, a physiological trait in some plants that inhibits hyphal penetration by soil pathogens such as Phytophthora. Preliminary histochemical observations on first- and second-order roots revealed that the most resistant cultivar, ‘Summit’, had less suberin in the root exodermis than blackberry, considered completely resistant to Phytophthora, but significantly more suberin than the least resistant cultivar, ‘Malahat’. The work is ongoing, but so far, it appears that root rot resistance may be related to both rapid root production and deposition of suberin in the exodermal layer of the root cortex. If this is the case, the traits could be selected during breeding to increase raspberry resistance to root rot.