1 - About Sclerotinia
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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
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
Beniwal, S. P. S., Baya's, B., Weigand, S., Makkouk, Kh., Saxena, M. C. 1993. Field Guide to Lentil Disease and Insect Pests.
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,
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,
INFORMATION PROVIDED BY:
Weidong Chen and Fred Muehlbauer
Grain Legume Genetics and Physiology Research Unit
USDA-Agricultural Research Service
303 Johnson Hall,
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