What is the Fungal Disease in Millets?

Globally, fungal diseases are responsible for approximately 30% of all crop diseases. Various fungal pathogens, such as downy mildew, ergot, and smuts, can significantly impact millets, leading to major yield reductions and economic losses for farmers.

Quick Summary

Millets are affected by several significant fungal pathogens including downy mildew, ergot, and various types of smut, which lead to stunted growth, malformed grains, and reduced yields. Effective management relies on using resistant cultivars, cultural practices, and fungicides to combat these crop threats.

Key Points

• Downy Mildew: Caused by Sclerospora graminicola, this disease leads to stunted growth and the characteristic 'green ear' malformation in millets.

• Ergot: The fungus Claviceps fusiformis produces a sticky 'honeydew' on millet florets, which later develops into toxic, kernel-replacing sclerotia.

• Smut: Fungal pathogens like Moesziomyces penicillariae replace individual millet grains with dark, spore-filled sacs called sori.

• Integrated Management: Effective control relies on a combination of resistant cultivars, good field sanitation, and strategic use of fungicides.

• Economic Impact: Fungal diseases can cause severe yield losses and contaminate grain, posing economic and health risks.

• Environmental Factors: High humidity and moderate temperatures are key conditions favoring the development and spread of many fungal diseases in millets.

Common Fungal Diseases Affecting Millets

Millets are hardy crops known for their resilience in marginal environments, but they are not immune to diseases, particularly those caused by fungi. Among the most damaging are downy mildew, ergot, and smuts, which can cause severe economic losses if not properly managed. The specific fungal disease in millets can vary by the millet type and the prevailing environmental conditions.

Downy Mildew

Downy mildew, also known as 'green ear' disease, is one of the most destructive fungal diseases of pearl millet. The pathogen responsible is Sclerospora graminicola.

• Symptoms: Early infection symptoms typically appear as pale, yellow (chlorotic) streaks on the leaves. A characteristic downy, fungal growth may be visible on the underside of infected leaves, especially in humid conditions. In severe cases, the inflorescence (ear) becomes malformed, transforming into a twisted, green, leafy structure, hence the name 'green ear'.
• Conditions: The disease thrives in high humidity and moderate temperatures, with oospores in the soil acting as the primary source of infection.
• Impact: Systemically infected plants become stunted and may produce little to no grain, leading to substantial yield loss.

Ergot

Ergot is a floral disease, mainly affecting pearl millet during the flowering stage. The causal agent is Claviceps fusiformis.

• Symptoms: The most visible symptom is the excretion of a creamy or light pink, sugary liquid called 'honeydew' from the infected florets. This attracts insects and promotes the growth of other saprophytic fungi, which can turn the panicle black. Over time, the honeydew dries and hardens into dark, sclerotial bodies that replace the grain kernels.
• Conditions: The disease is most prevalent in cool, wet weather during flowering, and the sclerotia can overwinter in the soil to cause future infections.
• Impact: Ergot not only reduces grain yield but also produces toxic alkaloids in the sclerotia, which can be poisonous to humans and animals if consumed.

Smut

Several species of fungi cause smuts in millets, each with slightly different symptoms and host specificity. In pearl millet, the fungal pathogen is Moesziomyces penicillariae.

• Symptoms: The pathogen infects individual ovaries, converting them into larger, oval-shaped sori (spore sacs) that are initially bright green but turn brown to black. The sori eventually rupture, releasing millions of dark spores.
• Conditions: Smut is often more severe in single-cross hybrids than in open-pollinated varieties and is most prevalent during flowering time.
• Impact: Smut directly replaces the grain with fungal sori, leading to significant reductions in grain quality and yield.

Other Fungal Diseases

Beyond the major diseases, millets can also be affected by other fungal pathogens, including:

• Rust (Puccinia substriata): Causes reddish-brown pustules on the leaves, which can lead to premature leaf death and reduced grain filling.
• Grain Mold: Caused by various fungi like Fusarium, Curvularia, and Aspergillus species, this disease leads to discoloration and deterioration of the grains under humid conditions during harvest.
• Blast (Pyricularia grisea): Affects leaves, necks, and heads of millets, especially finger millet, causing diamond-shaped lesions and potentially significant yield loss.

Management Strategies

Controlling fungal diseases in millets requires an integrated approach that combines genetic resistance, cultural practices, and chemical control.

Genetic Control

• Use of resistant cultivars is the most effective and sustainable long-term solution. Research institutions often develop and release new varieties with enhanced resistance to local pathogens. For example, marker-assisted breeding has been used to improve downy mildew resistance in pearl millet.

Cultural Practices

• Crop Rotation: Alternating millets with non-host crops can help reduce the buildup of fungal spores in the soil.
• Field Sanitation: Removing infected plant debris after harvest and burning or burying it can reduce overwintering inoculum.
• Timely Sowing: Sowing early can help crops escape peak infection periods for some diseases like smut.
• Seed Treatment: Using certified, disease-free seed and applying fungicide seed treatments can prevent seed-borne infections.
• Proper Drainage: Well-drained soil can reduce conditions favorable for downy mildew development.

Chemical Control

• Fungicide Application: In some cases, applying fungicides can be an effective control measure, particularly for seed-borne or foliar diseases. However, this should be done in accordance with local regulations and as part of an integrated strategy. For example, metalaxyl has been used to control downy mildew.

Comparison of Major Fungal Diseases in Millets

Feature	Downy Mildew	Ergot	Smut
Causal Agent	Sclerospora graminicola	Claviceps fusiformis	Moesziomyces penicillariae
Affected Plant Part	Leaves, inflorescence	Florets, grains	Individual grains
Key Symptom	Green, leafy malformation of the ear	Sticky 'honeydew' on florets, sclerotia	Spore sacs (sori) replacing kernels
Yield Impact	Stunted growth, total sterility	Replaced kernels, toxic alkaloids	Replaced kernels
Primary Spread	Oospores in soil, sporangia via wind/water	Ascospores via wind, conidia via rain/insects	Teliospores via wind, sporidia via wind
Prevention	Resistant varieties, seed treatment	Floating sclerotia from seed, resistant types	Certified seed, crop rotation

Conclusion

Fungal diseases like downy mildew, ergot, and smut pose a persistent threat to global millet production. These pathogens can cause significant yield and quality losses through varied and specific symptomatic damage. However, through diligent application of integrated disease management strategies, including the use of genetically resistant varieties, improved cultural practices like crop rotation, and targeted chemical control when necessary, the impact of these diseases can be minimized. For comprehensive management, farmers and researchers can consult resources such as the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) for the latest research and best practices.

Frequently Asked Questions

What is the most common fungal disease in pearl millet?

The most common and destructive fungal disease in pearl millet is Downy Mildew, caused by the pathogen Sclerospora graminicola.

How can you identify ergot in millets?

Ergot can be identified by the initial appearance of a creamy or pinkish 'honeydew' liquid oozing from infected florets, which later turns into dark, hard structures called sclerotia that replace the grain.

Does fungal disease in millets affect human health?

Yes, some fungal diseases like ergot produce toxic alkaloids in the grain. Consuming contaminated millet can cause 'kodo poisoning' in humans and livestock, leading to health issues.

What does a millet plant with downy mildew look like?

A millet plant with downy mildew will typically show pale or yellow streaking on the leaves. In later stages, the ear may be replaced by a twisted, green, leafy mass, an ailment known as 'green ear'.

Can crop rotation prevent millet diseases?

Yes, crop rotation is an effective cultural practice that helps manage fungal diseases by reducing the concentration of fungal spores in the soil over time.

What conditions favor fungal diseases in millets?

Fungal diseases like downy mildew and ergot are often favored by high humidity and specific temperature ranges during critical growth periods, such as the flowering stage.

Are there resistant millet varieties available?

Yes, research and breeding programs, including those at ICRISAT, have developed and released millet varieties with high levels of resistance to major fungal diseases like downy mildew.