Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2008
Publication Date: 8/27/2008
Citation: Porter, L., Hoheisel, G., Coffman, V.A. 2008. Resistance of Peas to Sclerotinia sclerotiorum in the Pisum Core Collection. Plant Pathology. 58:52-60. Interpretive Summary: White mold, caused by the fungus Sclerotinia sclerotiorum, can be a major foliar disease of both irrigated and dryland peas in the Pacific Northwest and Midwest of the United States of America. The disease is favored by cool, wet and humid conditions following row closure, especially when vine growth is heavy, overhead sprinkler irrigation is used, or rainfall is excessive. White mold of peas is currently managed through an integrated approach which includes: use of fungicides applied during flowering; planting disease-free seed; using three to five year rotations with non-host crops; deep plowing of sclerotia in infested soils; and promoting open-vine habits to limit humidity within the canopy Several of these measures such as long-term rotation and deep plowing are not practical in many growing areas, and due to poor economic returns to pea growers, foliar fungicides are cost prohibiting for many growers. Since cultural and chemical management tools are either less effective or expensive, the development of resistant pea cultivars to effectively manage white mold is a potentially advantageous but currently unavailable management practice. The present study developed a technique to rapidly screen pea lines for resistance to white mold. Twenty-two pea lines with resistance to S. sclerotiorum were identified that can be used by pea breeders to develop resistant pea cultivars to this pathogen. Pea lines with large stem diameters were found in this study to be more resistant to the white mold pathogen than lines with smaller diameters.
Technical Abstract: White mold, caused by Sclerotinia sclerotiorum, can be a major disease of irrigated and dryland peas. Management of white mold in peas is challenging because foliar fungicides are cost prohibiting to many pea growers, sclerotia survive for long periods of time limiting the effectiveness of crop rotations, and resistant or tolerant pea lines are not available. Therefore, identifying resistant lines is essential to improving disease management. In this study, 498 pea accessions from the Pisum core collection located at the USDA-ARS, Western Regional Plant Introduction Station (WRPIS), Pullman, WA and seven woody-stem pea lines from a private collection in the United Kingdom, were screened for resistance to white mold. Twenty-two pea accessions and one woody-stem line were identified with partial resistance to white mold. Pea accessions, 103709, 166084, 169603, 240515 and 270536 from the core collection demonstrated the greatest partial resistance to S. sclerotiorum based on nodal resistance and plant survival in replicated greenhouse and laboratory tests. Mean lesion length of only 5 of the 504 lines screened was between 0 to 1 cm when assessed three days post-inoculation. Not a single Pisum line was immune to infection and 237 of the 504 lines screened were highly susceptible and did not survive two weeks post-inoculation. Pea stem diameter was significantly (P ' 0.03) negatively correlated with stem lesion length in replicated greenhouse and laboratory experiments and was determined to be the best predictor of partial resistance to S. sclerotiorum based on lesion length.