Rice is a gift from the earth for more than half of the people in the world. But a leaf curse called rice rust poses a threat to farmers' livelihoods and nutrition to countless stomachs. Made by the fungus Magnaporthe oryzae, rice rust can destroy the entire plant if left to function.
In this article, I aim to explain the roots of rice rust, its signs, impacts, and ways to overcome it. My hope is that more can be done to stop the spread of rice rust and ensure livelihoods remain strong for the billions of people who depend on rice.
What is Rice Blast Disease?
Rust on rice is called "the dirtiest rice curse in the world". For many rice traders in Asia and other countries, this worry is always lurking in their fields. This fungus spreads quickly when weather permits, disrupting growth at any stage.
At night, when the air is cool and the leaves are wet with dew, this is the time it prefers to spread its seeds in secret. At dawn, spots may appear on leaves, stems or grains, damaging tissue and reducing yields. In a matter of days, a full field will be wasted if left alone.
Although rice rust has been a curse for farmers since time immemorial, the threat is growing with increasing global warming and erratic rainfall. Warmer weather and more travel spread it to new places, while relying on just a few varieties makes its growth vulnerable.
The Causal Agent: Magnaporthe oryzae
The fungus that causes rust on rice, Magnaporthe oryzae is one of the most talented enemies in the world. Fungi of the Ascomycota type, 'twill curse most types of rice and other grassy plants. M. oryzae makes a craft framework called a cradle that allows it to have cuticles and live inside it. Inside these cells form spherical seed carriers known as conidiophores that hold strings of spores called conidia.
Warm, humid air is most pleasant, with daily temperatures between five and twenty degrees and leaf wetting for at least eleven hours. This fungus resides among plants as a dormant skeleton in the foliage of rice or grassy plants that it may curse.
Symptoms of Rice Blast Disease
Rice blast causes several characteristic symptoms that allow it to be identified. Leaf blast appears as tan-colored, oval-shaped lesions on rice leaves. Lesions may reach over 1cm in length and are typically surrounded by a dark border. On leaf sheaths and stems, lesions appear as elongated, dark brown spots. In its most destructive form, neck blast infects the lower culm and neck region, preventing heads from emerging or forming grain.
On rice grains, the disease appears as small, brown dots. These dots enlarge to form gray centers with brown margins, a symptom known as panicle blast. Infected panicles emerge prematurely from boot leaves in a bleached appearance. Under severe outbreaks, entire leaves, stems or panicles may wither and die, leaving paddies full of dead stubble.
Impacts on Global Rice Production
Rice blast is considered the most important disease of rice worldwide due to the crop losses it causes annually. The Food and Agriculture Organization of the United Nations estimates average global rice yield losses of 10-30% where the disease is present, with potential losses of over 50% possible under severe epidemics. This amounts to tens of millions of tons of rice lost each year - rice that is desperately needed to feed the global population.
Asia is particularly at risk, as 90% of the world's rice is produced and consumed there. Countries like China, India, Indonesia, Japan, the Philippines and Vietnam suffer major losses from rice blast on a regular basis. In Africa too, outbreaks are on the rise and threatening food security. With a changing climate expanding its habitat further, experts fear rice blast may begin to impact regions like Brazil and the US which have so far seen only occasional incursions. Protecting vulnerable rice-growing areas from this disease is an urgent priority.
Effective & Best Practices to Prevent and Control Rice Blast Disease
1. Biological Control of Rice Blast
The first stand for obtaining rice rust lies in the use of small living creatures that hinder the survival of the cursed person. A variety of bacteria and fungi have shown promise as earth-endowed creatures for controlling M. oryzae numbers.
Trichoderma harzianum is a beneficial fungus commonly used as a biofungicide. It competes for space and nutrients with the rice blast fungus, as well as producing antibiotics. Soil applications of T. harzianum have significantly reduced disease severity under field conditions. Other microbes like Streptomyces spp. and non-pathogenic Fusarium spp. also exhibit biocontrol properties against M. oryzae. Using such antagonists offers a natural, eco-friendly approach to managing rice blast in an integrated manner.
2. Chemical Control Methods
When the disease is in full swing, spraying the bounty of the soil can help remove the curse. A wide variety of earthen gift crafts are permitted to bind rice rust, from mancozeb and earth salt blunt work to cursed shift-slowing triazoles, and carbamate work on methyl thread. Experiments show that all drugs can kill M. oryzae, but mancozeb and propiconazole are most widely used worldwide.
However, over-reliance on fungicides also risks promoting resistance in the pathogen population over time. Combining two effective fungicides from different classes can delay resistance development compared to single active applications. Integrating fungicides judiciously as part of an overall integrated disease management strategy helps maximize control while minimizing resistance risks.
3. Mechanical and Cultural Control Tactics
Cultural practices and physical barriers also play an important role in rice blast management. Proper drainage, irrigation and aeration help prevent conditions favorable for disease development. Removing rice debris after harvest removes the primary source of inoculum for the next crop. Crop rotation with a non-grass break crop like mungbean or soybean for one to two seasons helps disrupt the disease cycle.
Early planting of disease-resistant varieties enables crops to escape peak infection periods. Narrow row spacing and higher seeding rates promote rapid canopy closure that physically shields lower leaves. Burning rice straw rather than incorporating it into soil reduces the amount of inoculum recycled back into fields each season. Physical barriers like plastic or woven mulches placed over seedbeds fend off initial splash dispersal of spores.
4. Host Plant Resistance
Breeding rice varieties with genetic resistance to M. oryzae offers the most economical and environmentally friendly method of control. To date, over 30 major resistance genes (R genes) that confer resistance to certain M. oryzae races have been identified. Pyramiding two or more R genes into elite varieties using marker-assisted selection stacking provides broad-spectrum resistance that is more durable over time. Varieties with the Piz-5, Pi9 and Pita-3 genes, for example, maintain high levels of resistance even after years of cultivation.
However, the rice blast fungus is constantly evolving new virulent races capable of overcoming individual R genes. Therefore resistance breeding requires continuous effort to stay ahead of the pathogen. Combining host resistance with integrated disease management tactics offers the best long-term strategy for controlling this ever-changing disease.
Conclusion
By spreading the word about the impact of rust on rice and our commitment to it, I hope that more new coins and crafts will be produced to achieve this important goal. There are still many left, but with will and fellowship I believe we can limit its spread and protect the earth's most needed gifts for future generations.
Thank you for sharing this news - I hope it proves useful.
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