White mold of lentil occurs from early flowering to pod setting, usually in highly productive fields with tall, dense stands of lentils. The disease is favored by wet and cool conditions especially on lower ground where dense canopies usually develop. Because winter lentils are exposed to the prolonged wet and cool spring weather, white mold is likely to be more common and more severe in winter lentils than in spring-sown lentils.
Lentil plants infected by white mold first appear bleached near infection site on stems, leaves and stems turn brown to tan, die prematurely. Infected areas are covered with white fluffy mold on infected area Figure 1 (JPEG; 17.5Kb). Dark brown to black sclerotia develop inside and often outside of the infected plants Figure 2 (JPEG; 16.8Kb).
The pathogen that causes white mold is the fungus Sclerotinia sclerotiorum. It produces sclerotia that survive adverse conditions Figure 3 (JPEG; 5.48Kb). Sclerotia are hard and black bodies of mycelium, irregular in shape and like mouse droppings in appearance. Inside the sclerotia is white to pink mycelium which can re-grow under favorable conditions. Under cool and moist soil conditions usually provided by dense canopy, sclerotia germinate either directly by means of mycelium which can infect adjacent lentil plants or they produce small mushroom-like structure called apotheria, which eject ascospores into the air through wind or rain splash. The ascospores will land on lentil plants and start new infection. This pathogen is known to infect more than 400 plant species. A population of the white mold pathogen obtained from a single lentil field from eastern Washington showed considerable genetic diversity as measured by mycelial incompatibility.
The sclerotia survive in the soil. During cool and wet conditions, sclerotia can germinate by means of mycelium and infect plant roots. More often, under dense conopy which provides moist and cool conditions, sclerotia germinate by means of mushroom-like apothecia. Apothecia produce and eject ascospores into the air and ascospores may land on plants and start new infection. Infected plant become brown and tan in the infected area and the plant may wilt. Under dense plant conditions, white fluffy mycelium develop on affected areas, hence the disease name white mold. The fungus develops more sclerotia on infected plants. During harvest the sclerotia can be either shaken to the ground Figure 4 (JPEG; 891Kb) or collected with grains. Seeds contaminated with sclerotia may spread the disease to new production areas.
Although all lentil cultivars are susceptible to infection by S. sclerotiorum, cultivars do show different tolerance levels to this disease. Field and greenhouse evaluations of lentil cultivars have shown that significant differences in response to white mold exist among lentil cultivars. Certain cultivars performed consistently better than others in both field and greenhouse conditions conducted in Washington and Oregon. The cultivars that consistently showed tolerance to white mold include Pennel and CDC Sovereign. In fields where white mold is of a problem in the past, cultivars with tolerance to white mold should be selected for planting as a disease management practice.
- Plant lentils in fields where no white mold is observed previously and plant seeds free of sclerotia.
- Long term (five year or longer) rotation with cereal crops (but not with other legumes) will help reduce inoculum potential. The pathogen does not infect common cereal like wheat, barley, but it infects other legumes and crucifers like peas, and canola.
- Plant lentil cultivars that show some tolerance to white mold. Cultivar Pennel is more tolerant to white mold in our greenhouse and field evaluations.
- For seed production and in areas where the disease is very severe, fungicides may be sprayed. Fungicides Ronilan and Endura showed strong inhibition of white mold growth in our laboratory tests. Check fungicide restrictions before spraying.
Beniwal, S. P. S., Baya’s, B., Weigand, S., Makkouk, Kh., Saxena, M. C. 1993. Field Guide to Lentil Disease and Insect Pests. International Center for Agricultural Research in the Dry Areas, Aleppo, Syria 107 pages.
Chen, W., Grunwald. N., McPhee, K. and Muehlbauer, F. 2003. Field evaluation of lentil cultivars for resistance for Sclerotinia sclerotiorum, 2002. Biological and Cultural Tests for Control of Plant Diseases (online.) Report 18:F010. DOI:10.1094/BC18. The American Phytopathological Society, St. Paul, MN.
Chen, W., Grunwald, N., McPhee, K. and Muehlbauer, F. 2003. Evaluation of lentil cultivars for resistance to white mold. 2003 Sclerotinia Initiative Annual Meeting Abstract Page 17.
Chen, W., Myers, J., McPhee, K. and Muehlbauer, F. 2005. Field Evaluation of Lentil Cultivars for Tolerance to Sclerotinia sclerotiorum, 2004. Biological and Cultural Tests for Control of Plant Diseases (online.) Report 20: Submitted. The American Phytopathological Society, St. Paul, MN.
INFORMATION PROVIDED BY:
Weidong Chen and Fred Muehlbauer
Grain Legume Genetics and Physiology Research Unit
USDA-Agricultural Research Service
303 Johnson Hall, Washington State University
Pullman, WA 99164