Diseases of rice have affected not only the quantity but also the quality of the rice produced, leading to economic losses and food security concerns. Rice, a staple crop of immense importance, plays a vital role in agriculture and the economy. However, like any crop, rice cultivation faces its share of challenges, particularly in the form of various diseases that can plague the fields and threaten yields.
What are the Major Diseases of Rice?
These are important diseases of rice as given below
List of rice diseases
- Brown spot of Rice
- Rice blast
- Bacterial leaf streak of rice
- Bakanae Disease of Rice
1. Brown Spot of Rice
The causal organism is Bipolaris oryzae
Symptoms
Usually, the host plant’s leaves and glumes are affected. oval lesions 1 cm long are present on the leaves. When completely matured, the dots are brown with a greyish centre. When conditions are favourable for sporulation, glumes develop velvety black or dark lesions. Black patches on the endosperm may result from glume lesions. Leptocorisa oratorius, rice bugs may feed on insects causing damage to the grain.
Epidemiology:
- Temperature: 21-26 °C
- Relative Humidity: 90 %
Disease Cycle:
The fungus may live for up to 4 years in seeds. By sowing contaminated seeds, infected seedlings are produced, from which fungal spores can spread by wind or air and infect other plants. Weeds and plant waste are additional hosts for fungus spores.
How to control:
- Managing brown spots begins with increasing soil fertility.
- Regular monitoring of soil nutrients.
- Use resistant varieties of plants.
- Use fungicides as seed treatments such as iprodione, propiconazole, azoxystrobin, trifloxystrobin, and carbendazim.
- Before planting, prepare seeds by soaking them in hot water (53–54°C) for 10–12 minutes to reduce the risk of primary infection during the seedling stage.
2. Rice Blast
The Causal Organism of Rice blast is pyricularia oryzae
Epidemiology:
Heavy rainfall
fertilizers having a high nitrogen level.
Symptoms:
Occasionally, this condition can be referred to as Pyrricularia blight or rotting neck, which is typically present wherever rice is cultivated. On leaves, nodes, panicles, grains, and occasionally on leaf sheaths, little dots emerge. The blotches start out as tiny, wet, whitish, greyish, or bluish specks. These spots grow quickly and turn grey in the middle. Inflorescence and glumes can also develop brown to black patches. Diseased heads seem blasted and pale in colour in later stages. Panicle development becomes disrupted and they droop.
Disease cycle:
A spore from the pathogen causes lesions or patches on rice plant sections like the leaf, leaf collar, panicle, culm and culm nodes. The pathogen enters the plant through a structure known as an appressorium. The contaminated rice tissue then produces spores of M. grisea, which are disseminated as conidiospores. When the conditions are right, a cycle can be finished in approximately a week and one lesion can produce thousands of spores in a single night. Rice crops that are prone to rice blast lesions might suffer catastrophic losses because the lesions can continue to release spores for more than 20 days.
How to control:
- Growing resistant types of plants is the primary method of blast control.
- Additional crop management practices include changing the timing of planting Whenever feasible, plant seeds as soon as the rainy season begins.
- Blasting can be decreased by adding silicon fertilizers to soils that lack silicon, such as calcium silicate.
- To reduce blast, systemic fungicides such as triazoles and strobilurins can be used carefully.
3. Bacterial Leaf Streak of Rice
Bacterial leaf streak is caused by Xanthomonas oryzae pv. oryzicola.
Epidemiology:
- Temperature 26-30 °C
- Irrespective of relative humidity
Symptoms:
Small, water-soaked, linear lesions between leaf veins are the first signs of the condition. Initially dark green, these streaks later turn light brown to yellowish grey. When held up to the light, the lesions appear translucent. In really severe cases, entire leaves may turn dark and die. On the surface of leaves, yellow droplets of bacterial ooze that is packed with bacterial cells can be seen in humid conditions. Lesions with leaf streaks are typically more delicate than those with narrow dark patches. Lesions of small dark spots don’t produce bacterial slime or appear translucent.
Disease cycle:
During its life cycle, the disease can also be spread by plant-to-plant contact the disease is primarily spread by seed. In rainy conditions and toward the end of the growing season, epidemics are often seen. The pathogen is released from the inoculated seed more easily when it is moist, which promotes leaf colonization and tissue invasion. Bacteria from the wet leaf surface enter the plant through the stomata or other leaf holes, such as wounds. The bacteria may survive the winter in the soil after the plant is harvested or dies, but their survival rate is significantly higher when there is crop detritus present. Weeds and annual plants’ clean seeds could become infected again by leftover germs from the soil, trash, or other plants.
How to control:
- Resistant varieties of plants.
- Use hot water to treat the seeds.
- In maintaining an organized field weed hosts should be removed, and volunteer seedlings, straws, rice ratoons and rice stubble should be plowed under to prevent the bacteria from infecting them.
- Utilize a variety of plant nutrients in moderation, particularly nitrogen. Make sure that fields (in conventionally flooded crops) and nurseries have good drainage.
- When there are severe floods, drain the field.
- In order to eradicate the bacteria in the soil and plant leftovers, dry the land during the fallow season.
- A copper-based fungicide sprayed at the heading can be useful in treating the disease in cases of severe infection, when yield may be impacted.
4: Bakanae Disease of Rice
The disease is caused by Fusarium moniliforme
Epidemiology:
- Temperature 26 °C
- Yield loss 20-50%
Symptoms:
The disease, also known as a white stalk, is typically found anywhere rice is farmed. Thin and chlorotic infected seedlings may perish before or after transplantation. Infected plants in the field have few tillers and quickly lose their leaves. Panicles on living plants are empty. While the most common symptom of this illness is the aberrant elongation of these affected plants in seed beds or fields, some infected plants may be stunted instead of elongated.
Disease Cycle:
Although the overwintering pathogen in plant waste or soil may potentially operate as the principal inoculum in the next season Bakanae a monocyclic disease, is primarily spread through infected seeds from the preceding cropping season. The fungus that causes the disease can exist for a very long time since it is soil- and seed-borne.
Control:
Cultural control:
Before planting
- After two years, alternate rice with resistant crops like vegetables or root crops.
- Use contaminated- and infection-free certified seed. Use a seed dressing if sure.
CHEMICAL CONTROL
- To remove spores on the surface of seeds, use thiram or thiram combined with thiophanate-methyl.
- The azole and strobilurin individuals of fungicides are also effective.
1.Hafiz M Rizwan Mazhar, 2.Dr. Kamran Saleem
Nuclear Institute of Agriculture and Biology, Faisalabad
