Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2011
Publication Date: 5/20/2011
Citation: Okubara, P.A., Jones, S.S. 2011. Seedling tolerance to Rhizoctonia and Pythium in wheat chromosome group 4 addition lines from Thinopyrum spp. Canadian Journal of Plant Pathology. 33(3): 415-422. Interpretive Summary: Soilborne pathogens, including Rhizoctonia solani and R. oryzae, are important biotic factors that reduce crop health and yield in dryland cereal production systems of the U.S. Pacific Northwest (PNW) of the United States and worldwide. Both pathogens cause Rhizoctonia root rot and bare patch, seedling diseases of wheat that result in chronic yield losses of 10 to 15% and up to 50% in direct seed production systems in the PNW. These diseases continue to pose challenges to growers due to a lack of adequate control measures. Genetic resistance is an effective and sustainable means of disease control, constitutively protecting the plant from damage and reducing the need for seed treatment, fungicide application and/or tillage. Here, we developed a combination of visual and quantitative assessments of disease severity to demonstrate enhanced tolerance to R. solani and R. oryzae in the bread wheat cultivar ‘Chinese Spring’ that harbors additional copies of chromosome 4 from the grass relative Thinopyrum.
Technical Abstract: Chromosome 4 from Thinopyrum spp. confers regrowth after a sexual cycle and senescence in hexaploid wheat (Triticum aestivum), and is associated with resistance to the necrotrophic eyespot pathogen, Tapesia yallundae. We sought to determine whether robust root growth or other traits expressed in chromosome 4 addition lines enhanced tolerance to necrotrophic root pathogens. To this end, we tested seedlings of wheat cultivar ‘Chinese Spring’ (CS) carrying chromosome 4E from Th. elongatum or 4J from Th. bessarabicum for response to Rhizctonia solani AG-8, Pythium ultimum, or P. irregulare. Seedling response was evaluated on the basis of disease severity, first leaf length, root weight and total root length after 14 days of growth in infested soil. The CS4E addition line displayed the best Rhizoctonia tolerance, with disease severity ratings of 2.2 to 3.0, no significant decrease in root weight, and 5 to 41% decrease in root length after pathogen challenge. In contrast, wild type CS showed disease severity ratings of 3.5 to 4.1, a 13% decrease in root fresh weight, and 55% decrease in root length. CS4E also exhibited the best tolerance to P. ultimum. Addition line CS4J and amphidiploid CS-Th. elongatum displayed moderate tolerance to R. solani AG-8 and P. ultimum. None of the lines were tolerant to P. irregulare. Our findings indicate that chromosomes 4E and 4J encode genetic sources of seedling tolerance to two soil-borne pathogens. Although Thinopyrum chromosomes do not recombine freely with wheat chromosomes, these novel sources of resistance should prove valuable to wheat improvement programs.