৪৯তম বিসিএস ⎯ কৃষিবিজ্ঞান [৮০১]

Tungro is a complex of two viruses, Rice tungro bacilliform virus and Rice tungro spherical virus, transmitted by green leafhoppers.

The fungal pathogen Phytophthora infestans is responsible for causing late blight of potato. This is a highly destructive disease that can rapidly destroy entire potato crops.
​Early Blight of potato-  Fungus Alternaria solani
​Symptoms:
​The appearance of dark, water-soaked lesions on the leaves, which quickly expand and cause the plant to collapse. 
​Infected tubers develop a reddish-brown, dry rot that renders them inedible.

Wilting of jute – Usually caused by a fungus (Macrophomina phaseolina), not a virus.

Leaf roll of potato – Caused by Potato leafroll virus (PLRV) → viral disease 

Red rot of sugarcane – Caused by a fungus (Colletotrichum falcatum), not viral.

Damping off disease of seedling – Usually caused by fungi like Pythium or Rhizoctonia, not viral.

Bacteriophage is a virus that specifically infect bacteria.
​Oomycete (Phytophthora infestans) one kind of fungus. 

Smut disease of sugarcane
​✓Emergence of a long, whip-like black structure (smut whip) from the growing point of the cane.
✓ Reduction in number and size of leaves; leaves become narrow and erect.
✓ Stunted and thin canes with reduced internode length and small grassy shoots.
✓ In severe cases, clumps become bushy due to excessive tillering of weak shoots..

The characteristic 'silver shoot' or 'onion leaf' symptom is caused by the larval feeding of the rice gall midge inside the plant's tillers.

Dithane M 45 / Carbendazim is a widely used systemic fungicide that is very effective against a broad range of fungal diseases, including anthracnose caused by the fungus Colletotrichum gloeosporioides. 
​Urea: Urea is a nitrogen-based fertilizer used to provide nutrients to plants. 

Malathion: Malathion is an insecticide used to control a variety of insect pests. I

Copper sulphate: Copper compounds are effective fungicides, but the formulation and application method are critical.

The larvae of the weevil bore into the jute stem, which disrupts the plant's vascular system, hindering the transport of water and nutrients to the upper parts of the plant. This blockage leads to wilting, and in severe cases, the affected part of the stem may break off. 
​Symptoms of attack by the jute stem weevil :
​1. Wilting of the plant's top portion.
2. Knot-like swellings or galls on the stem.
3. Stunted growth and excessive branching.
4. Breakage of the stem at the point of damage.

Loose smut is a fungal disease caused by Ustilago tritici. It specifically affects the head (spike) of the wheat plant, replacing the healthy kernels with a black, powdery mass of spores. These spores are easily dispersed by wind, which leads to the infection of other healthy plants.

Red Rot
Pathogen: Colletotrichum falcatum (a fungus)
Transmission: The fungus can live inside the cane stalks. If infected stalks are used as seed, the disease is transmitted to the new crop.

Smut
Pathogen: Ustilago scitaminea (a fungus)
Transmission: The fungus can survive as mycelium (dormant fungal threads) in the setts. 

Ratoon Stunting Disease (RSD)
Pathogen: Leifsonia xyli subsp. xyli (a bacterium).
Transmission: This disease is transmitted through infected setts and is difficult to detect because it shows no external symptoms. 

The causal agent is primarily the fungus Colletotrichum gloeosporioides

Bordeaux mixture (Chemical fungicide made by mixing copper sulfate and quicklime in water.)

Rice Stem Borer 
​The adult yellow stem borer is a type of moth.
✓ The female moth lays eggs near the tip of the rice leaves.
✓ After the eggs hatch, the larvae enter the stem and cut downward inside the stem.
✓ If the damage occurs before the panicle emerges or during the vegetative stage, it is called “Deadheart.
✓ ”If the damage occurs at the time of panicle emergence, it is called “Whitehead.

Leaf rust is a fungal disease caused by the pathogen Puccinia triticina. It is characterized by the formation of circular to oval-shaped yellow to orange pustules on the leaves and stems of wheat plants. These pustules contain the spores of the fungus, giving them a dusty appearance.
​
​Loose smut replaces the wheat kernels with a black, powdery mass of spores.

Powdery mildew appears as a white, cottony or powdery substance on the leaves and stems.

Scab, also known as Fusarium head blight, causes bleaching and shriveling of the wheat spike and can produce pinkish-orange spore masses on the glumes.

Malathion: This is an organophosphate insecticide that is effective against a wide range of chewing and sucking insects, including caterpillars. It works by disrupting the nervous system of the insect.
​
​Carbendazim is a systemic fungicide.
Copper oxychloride is a copper-based, protective fungicide.
Mancozeb is a dithiocarbamate protective fungicide

BRRI dhan27 → This variety is salinity tolerant, Tungro virus Resistant variety.

BRRI dhan28 → A high-yielding Boro rice variety developed by BRRI, known for its blast resistance.

IR-8 → The famous “miracle rice” of the Green Revolution, but it is not blast resistant.

Pusa Basmati-1 → Known for aromatic quality, but it is susceptible to blast disease.

Damaging Symptoms of Top Shoot Borer of sugarcane (Scirpophaga excerptalis): 
✓ Caterpillars bore into the top shoots of cane.
✓ Central whorl leaves get bunched together, producing a
“bunchy top” or bunchy appearance.
✓ Leaves show parallel shot holes due to larval feeding in the folded leaves.
✓ Growth of the cane is stunted; internodes remain short.
✓ Severe infestation leads to production of multiple side shoots, reducing yield and quality.

Nature of Damage of Wheat Aphid:
✓ Sucks sap from leaves, stems, and growing points.
✓ Causes yellowing, curling, and stunted growth.
✓ Heavy infestation can reduce tillering and yield.
✓ Can transmit barley yellow dwarf virus.
✓ Most affected stage is grain filling stage ( This is the booting stage ) 

The bacterium causing bacterial leaf blight (BLB) can be transmitted through seeds, so using clean seeds is a critical preventative measure.
​Cultural Control measures:
• Planting resistant varieties.
• Using disease-free seeds.
• Hot water seed treatment (52-54°C for 30 minutes).
• Avoiding excessive nitrogen fertilizer.
• Maintaining balanced NPK application.
• Periodically draining fields.
• Removing infected plant debris and weeds.
• Maintaining proper plant spacing.

The disease is primarily caused by the root-knot nematode, Meloidogyne incognita. 
​They infect the roots, they cause the formation of characteristic swellings or "galls," which are why the disease is called "root-knot."

Fusarium moniliforme- Pokkah Boeng of Sugarcane 
​Ustilago scitamine- responsible for sugarcane smut. 
​Xanthomonas albilineans-Responsible of  sugarcane leaf scald. 

Soft rot is a common bacterial disease that affects many crops, including potatoes, carrots, and onions.
​Favored condition is high temperatures and high moisture or low oxygen conditions.
Symptoms of soft rot of potato: ​The tuber becomes a slimy, foul smelling mass. Liquid may ooze from the affected area.

Stem rot: Caused by the fungus Macrophomina phaseolina, this is the most devastating seed-borne disease of jute. 
​Anthracnose: Caused by the fungus Colletotrichum corchori, this disease results in dark, sunken spots on the stem, which can lead to cankers and fiber exposure.
​Black band: Caused by the fungus Botryodiplodia theobromae, this disease can also be transmitted through infected seeds, leading to various symptoms, including stem lesions and blackening

Control Methods of Rice Stem Borer:
✓ Collect and destroy the eggs.
✓ Destroy the infested shoots (deadhearts).
✓ Use light traps to catch and kill the moths.
✓ Allow insectivorous birds to sit in the field by spreading plant residues on the ground.
✓ If 10–15% deadhearts or 5% whiteheads are observed in the rice field, apply Sumithion 59 EC or Diazinon 60 EC at 1.5 L/ha on the soil.
✓ After harvesting, incorporate or burn the stubbles and residues into the soil.

অতিরিক্ত নাইট্রোজেন প্রয়োগ (Avoid excessive nitrogen application ): 
​অতিরিক্ত নাইট্রোজেন ব্যবহার করলে গাছের টিস্যুগুলো আরও নরম এবং রসালো হয়। এটি জাব পোকার জন্য একটি চমৎকার খাদ্য উৎস সরবরাহ করে, যা তাদের বংশবৃদ্ধি উৎসাহিত করে এবং দ্রুত সংখ্যা বৃদ্ধি ঘটায়। নাইট্রোজেনের ব্যবহার সীমিত রাখলে জাব পোকার সংখ্যা নিয়ন্ত্রণে রাখা যায়।

​মাঠে ক্রমাগত জল দেওয়া (Flooding the field continuously): 
​যদিও কিছু নির্দিষ্ট কীটনাশক নিয়ন্ত্রণের জন্য মাঠে জল দেওয়া হয় (যেমন ধানের ক্ষেত্রে), এটি গমের জাব পোকা দমনের জন্য কোনো প্রচলিত পদ্ধতি নয়, কারণ গম একটি শুষ্ক-ভূমির ফসল।

​পরিপক্বতার সময়ে গভীরভাবে লাঙল দেওয়া (Deep plowing at maturity): 
​এই পদ্ধতিটি সাধারণত মাটিতে থাকা নির্দিষ্ট কিছু কীটপতঙ্গ ও রোগ নিয়ন্ত্রণ বা পরবর্তী ফসলের জন্য জমি প্রস্তুত করার জন্য ব্যবহার করা হয়। এটি সরাসরি জাব পোকার উপদ্রব নিয়ন্ত্রণে কোনো ভূমিকা রাখে না, কারণ জাব পোকা গাছের উপরের অংশে থাকে।

​ছত্রাকনাশক (Fungicides) প্রয়োগ করা: 
​ছত্রাকনাশক হলো রাসায়নিক পদার্থ যা ছত্রাকজনিত রোগ প্রতিরোধের জন্য ব্যবহৃত হয়। জাব পোকা একটি পোকামাকড় এবং এর বিরুদ্ধে ছত্রাকনাশক সম্পূর্ণ অকার্যকর। পোকামাকড় দমনের জন্য কীটনাশক (insecticides) বা অন্যান্য কীট ব্যবস্থাপনা পদ্ধতি ব্যবহার করতে হয়।

Hot water and Bavistin both are used for seed treatment but Hot water is not a Fungicide. It is a method of physical seed treatment . Only Bavistin is the true fungicide whish is used for seed treatment. 

 Cultural practice helps in controlling jute stem rot: 
​1. Crop Rotation
2. Field Sanitation
3. Balanced Fertilization
4. Proper Drainage
5. Optimum Plant Spacing
6. Seed Treatment
7. Timely Sowing
​8. Deep ploughing 

Identifying Symptoms of Rice Blast disease:
✓ Diamond/ spindle-shaped lesions on leaves with gray or white
centers and brown or reddish brown borders.
✓ Lesions can also appear on the collar, nodes, and panicle neck.
✓ "Neck blast" causes the neck of the panicle to rot, which can lead to panicle breakage and failure to fill grains