Model Answer
0 min readIntroduction
Bajra ( *Pennisetum glaucum* L.) is an important millet crop grown in arid and semi-arid regions of India and Africa, providing food security for millions. However, its production is often hampered by various biotic and abiotic stresses, among which the ‘Green ear disease’ is a significant threat. First reported in Rajasthan, India, in 1978, this disease causes substantial yield losses, particularly during years with high humidity and rainfall. Understanding the disease etiology, epidemiology, and effective management strategies is crucial for sustainable Bajra production.
Understanding Green Ear Disease
Green ear disease of Bajra is a significant physiological disorder, not a classical disease caused by a pathogen. It’s characterized by the development of green, succulent, and elongated ears, often resulting in sterility and reduced grain filling. While initially thought to be caused by a virus, it's now understood to be a complex interaction between the plant genotype, environmental factors, and hormonal imbalances.
Etiology and Symptoms
The exact cause remains debated, but the prevailing theory points towards a disruption in the gibberellic acid (GA) metabolism within the plant. This disruption leads to abnormal ear development. Key symptoms include:
- Elongation of the ear: The ear becomes abnormally long and thick.
- Green coloration: The ear retains a green color even at maturity, unlike the normal brown or purple hues.
- Succulence: The ear becomes fleshy and succulent due to increased water content.
- Sterility: Pollen grains are often malformed or absent, leading to poor seed set.
- Reduced grain filling: Even if some pollination occurs, the grains are often shriveled and underdeveloped.
Factors Favoring the Disease
Several factors contribute to the development of Green ear disease:
- Genotype: Certain Bajra varieties are more susceptible than others. Hybrid varieties are generally more prone.
- Temperature: Moderate temperatures (25-30°C) favor the disease development.
- Humidity: High relative humidity (above 70%) during the flowering and grain filling stages is critical.
- Rainfall: Excessive rainfall during flowering can exacerbate the problem.
- Nutrient Imbalance: Deficiencies in zinc and boron have been linked to increased susceptibility.
- Plant Density: High plant density can create a microclimate conducive to disease development.
Disease Cycle
Since it's a physiological disorder, there isn't a traditional disease cycle involving pathogen reproduction. However, the process can be described as follows:
- Susceptible Bajra plants are exposed to favorable environmental conditions (moderate temperature, high humidity, rainfall).
- These conditions disrupt the GA metabolism within the developing ear.
- Abnormal ear elongation and succulence occur.
- Pollen development is affected, leading to sterility and reduced grain filling.
- The cycle is perpetuated through seed propagation from affected plants.
Management Strategies
Managing Green ear disease requires an integrated approach:
- Resistant Varieties: Utilizing Bajra varieties with inherent resistance to the disorder is the most effective strategy.
- Balanced Fertilization: Ensuring adequate supply of zinc and boron through soil application or foliar sprays.
- Sowing Time: Adjusting sowing time to avoid peak humidity and rainfall periods during flowering.
- Plant Density: Maintaining optimal plant density to improve air circulation and reduce humidity.
- Seed Treatment: Treating seeds with plant growth regulators (e.g., GA3) can sometimes mitigate the effects.
- Rouging: Removing affected plants from the field to prevent seed contamination.
Recent Research
Recent research focuses on identifying genes responsible for GA biosynthesis and signaling pathways in Bajra. Molecular markers linked to resistance are being developed to facilitate breeding programs. Studies are also investigating the role of epigenetic modifications in disease susceptibility.
Conclusion
Green ear disease of Bajra remains a significant challenge to pearl millet production in India and Africa. While the exact etiology is still under investigation, understanding the interplay between plant genetics and environmental factors is crucial for developing effective management strategies. Breeding for resistant varieties, coupled with improved agronomic practices, holds the key to minimizing yield losses and ensuring food security in regions reliant on this important millet crop. Further research into the hormonal regulation of ear development is warranted.
Answer Length
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