White mold of chickpea can occur at either seedling stage or at flowering and pod filling stages depending on the environmental conditions and possible the pathogen species involved. At seedling stage, the disease occurs at the base of the stem causing symptoms like collar rot. Often white mycelial growth around the stem on soil surface is visible Figure 1 (JPEG; 1.44Mb). Affected plants wilt and die Figure 2 (JPEG; 1.38Mb) and Figure 3 (JPEG; 1.38Mb). Black sclerotia in various shape and sizes form on dead or dying chickpea stems right above or below the soil line Figure 4 (JPEG; 1.21Mb). The disease at the seedling stage is common in central California in the early spring, and serious losses due to this disease have been observed there. However, in the Pacific Northwest and the northern Great Plains, the disease is more common at the flowering and pod filling stage (Chen et al. 2006). Infection starts at upper stem or on senescent flowers. Infected stems become pale in colour like bleaching, and the symptom spreading both upward and downward along the stems Figure 5 (JPEG; 633Kb). Under heavy canopy and humid conditions, white puff mycelial growth becomes conspicuous Figure 6 (JPEG; 313Kb) and Figure 7 (JPEG; 403Kb), and black irregular-shaped sclerotia may form and are visible on the stems. The plant parts above the infection wilt and die. Disease infected fields show appearance of chlorotic and dying branches or whole plants scattered in the field.
White mold of chickpea is caused by Sclerotinia sclerotiorum in the Pacific Northwest and the Great Plains. However, both S. sclerotiorum and S. minor are reported to cause white mold of chickpea in Arizona (Matheron and Porchas, 2000). The species of Sclerotinia responsible for the seedling stage disease in Central California could be different based on our preliminary studies and remains to be identified (Njambere et al., 2006). In all cases, the pathogens produce black and irregularly shaped fruiting bodies of sclerotia that survive adverse conditions, and the sclerotia can either germinate directly or produce apothecia and ascospores that can be spread by wind, land on plant parts and initiate new infection.
The disease cycle
All the pathogens survive adverse conditions or between crop seasons as the black sclerotia in soil or from infested seed lots. At appropriate conditions, the sclerotia may germinate by one of two means. Sclerotia can germinate directly by means of mycelium in the soil and infect chickpea stems. After appropriate conditioning like periods of low temperature and moisture, sclerotia could also germinate by means of apothecia bearing ascospores in asci. Ascospores are blown and spread by wind and land on stems or flowers to initiate new infection. Within season spread of the disease may occur directly from infected plant to health plants through direct contact under dense crop canopy conditions. In the case of stem base infection, the pathogen may spread to adjacent plants through mycelial growth under wet soil conditions if plants are close to one another (like 2 to 3 inches apart).
The disease at seedling stage is mainly caused by direct germination of sclerotia in the soil. Therefore management practices that can reduce sclerotial density in the soil will be effective in reducing the disease. Considering the longevity of sclerotia in soil and wide host range of the pathogen. Long-term rotations with cereal crops when possible will reduce the inoculum (sclerotia) density.
Chickpea cultivars in California do show differential reactions to white mold in the field. Some are more resistant or more tolerant than others based on field observations. Therefore, the tolerant cultivars should be chosen when possible especially in fields with history of white mold. However, specific experiments are needed to demonstrate and confirm the resistance/tolerance of the cultivars that seem to perform better in the field.
The disease at the flowering and pod filling stages is favoured by excessive vegetative growth and cool moist conditions. No resistance to this stage of disease has been observed among chickpea cultivars. Fungicide application could be an option used to control white mold, but the economical viability of fungicide application for controlling white mold on chickpea remains to be demonstrated. Rotation and agronomical practices that reduce or delay canopy closure will help reduce the disease.
- Chen, W., Schatz, B, Henson, B., McPhee, K. E., and Muehlbauer, F. J. 2006. First report of Sclerotinia stem rot of chickpea caused by Sclerotinia sclerotiorum in North Dakota and Washington. Plant Disease 90: 114. Link
- Matheron, M. E., and Porchas, M. 2000. First report of stem and crown rot of garbanzo caused by Sclerotinia minor in the United States and by Sclerotinia sclerotiorum in Arizona. Plant Disease 84: 1250. Link
- Njambere, E., Chen, W., Frate, C, Temple, S.R., and Muehlbauer. F.J. 2006. Diversity of Sclerotinia isolates from chickpea from central California. Phytopathology 96: S85. About
Grain Legume Genetics and Physiology Research Unit
Pullman, WA 99164