NPIPM:Root and crown rot
Authors: Byamukama, E., Wegulo, S., Ali, S., and Friskop, A.
Causal Organism
There are three diseases that affect the root, foot and crowns of wheat leading to premature ripening of infected tillers: Common root and foot rot caused by Bipolaris sorokiniana (also called Helminthosporium sativas/Cochliobolis sativus); Fusarium root, crown, and foot rot caused by Fusarium spp (mainly F. culmorum, F. pseudograminearum, and F. graminearum); and Take-all root and crown rot (usually called take-all) caused by Gaumanomyces graminis var. tritici.
Symptoms and Signs
Root, foot and crown rots are mostly noticed after heading, when infected plants ripen prematurely with bleached wheat heads. Additionally, infected plants will have crown and root discoloration and weakened root systems. To differentiate between the three different rots, examine the crown, the sub-crown and the lower nodes.
Common root and foot rot causes dark brown lesions on the subcrown. These lesions will eventually spread to encompass the entire subcrown internode. Severe infection can lead to pre-mature ripening of wheat head. But most of the time this disease goes unnoticed when tillers are not prematurely killed. Mildly infected plants have few tillers and may be stunted.
Fusarium root, crown and foot rot can develop from the roots and progress to lower nodes. This disease can also develop from above ground through leaf sheath and develop on the crown and lower nodes. Spitting the lower nodes and the crown of infected plants reveal a brown internal decay. Peeling off the leaf sheath may show chocolate brown to red discoloration of the lower nodes. Under severe infection, plants are killed and may resemble moisture stressed plants.
Take-all is relatively easy to diagnose, however, infected plants remain symptomless until heading. Infected plants have glassy black discolored roots and under wet conditions, this discoloration may extend to the first few lower nodes. Under severe infection, plants are stunted and ripen prematurely and these usually found in low laying areas of the field or under irrigated wheat production systems.
Disease Impacts
Root, foot and crown rots are usually inconspicuous and yield loss caused by this complex may be underestimated. Impact of these diseases may be great under other stress conditions such as moisture or heat stress. Yield losses of 3-7% are not uncommon, and may be higher for individual fields.
Life Cycle and Epidemiology
The fungi that cause root, foot, and crown rots are primarily soil- and residue-borne. Plants get infected early in the season as roots pass through the soil. Bipolaris sorokiniana infection is more common when seedlings are stressed by drought, high temperatures, freezing or flooding conditions. Fusarium spp. in addition to being residue- and soil-borne, can also survive on seed. The take-all pathogen also survives in the soil and plant debris and infection is favored by neutral to alkaline soil pH conditions.
Management Approaches
Rotating wheat with a non-host broadleaf crop such as soybeans, canola, dry beans or sunflowers can help reduce the inoculum. Seed treatments are effective in preventing seedling infections in the first 2-3 weeks. No resistant cultivars are available but some cultivars are less susceptible to these diseases. Planting in a firm mellow seedbed favors faster strong root growth that may tolerate some level of infection. Maintaining good agronomic practices such as good soil fertility program, drainage, and weed management help establish a healthy wheat crop.
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