Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2004
Publication Date: 9/20/2004
Citation: Higginbotham, R.W., Paulitz, T.C., Kidwell, K.K. 2004. Evaluation of adapted wheat cultivars for tolerance to pythium root rot. Plant Disease.88:1027-1032 Interpretive Summary: Pythium root rot is an important disease on wheat across all growing regions. In this study, we selected two of the most virulent isolates of Pythium in the Pacific Northwest, and developed a method to test germplasm in the greenhouse for tolerance to this disease. This disease does not produce distinctive symptoms on the root, but destroys feeder roots. Inoculum of the pathogen was mixed into pasteurized soil, along with a food base for the fungus, and pre-germinated seeds were transplanted into the containers. Root scanning software was used to calculate important root parameters such as root length and number of root tips. Thirty lines were obtained from spring wheat breeding programs throughout the U.S. Caledonia, Chinese Spring, MN97695 and OR942504 appear to be highly susceptible to Pythium root rot, whereas genotypes KS93U161, OH708 and Sunco were the most tolerant to this disease.
Technical Abstract: To date, no source of genetic resistance has been identified against Pythium species, a major root fungal pathogen of wheat (Triticum aestivum L.). In addition, no long-term, sustainable options for controlling Pythium root rot are available; therefore, identifying and then incorporating genetic resistance into wheat cultivars would create an ideal, effective and inexpensive method of control for this disease. The objective of this study was to examine, in a controlled growth chamber environment, the level of tolerance to Pythium root rot among a diverse set of wheat germplasm collected from all major wheat production regions in the United States, and to identify potential resistance gene donors for cultivar improvement. Pythium debaryanum isolate 90136 and P. ultimum isolate 90038, previously identified as the most virulent Pythium isolates on wheat, were used to infest pasteurized soil, which was seeded with wheat genotypes and placed in a growth chamber maintained at a constant 16°C, 12 hr photoperiod and ambient humidity. Length of the first leaf and plant height measurements were recorded, and roots were digitally scanned to create computer files that were analyzed using WinRhizo software. Significant (P < 0.05) differences in susceptibility were detected among wheat genotypes in the presence of both Pythium species, and a significant (P < 0.0001) correlation between plant stunting and root loss was detected. Based on both shoot and root measurements, Caledonia, Chinese Spring, MN97695 and OR942504 appear to be highly susceptible to Pythium root rot, whereas genotypes KS93U161, OH708 and Sunco were the most tolerant to this disease. Genetic characterization of these genotypes may prove useful in identifying resistance gene donors for future use in cultivar enhancement efforts.