Plant Sciences

Step 1: Composition.
Bordeaux mixture is a classic protectant fungicide formed by mixing copper sulphate (also called blue vitriol) and freshly prepared lime (calcium hydroxide) in water.
Step 2: Typical preparations and use.
Common field formulae include 1:1:100, 4:4:50, or 5:5:50 (copper sulphate : lime : water) depending on crop sensitivity and disease pressure.
The lime neutralizes the solution, reduces phytotoxicity, and helps the copper remain as finely dispersed copper hydroxide that adheres to plant surfaces.
Step 3: Why the other options are incorrect.
Lime with calcium sulphate does not provide the fungicidal copper ion needed for action.
Sulphur with lime is a different product (lime sulphur) used mainly against mites and some fungal pathogens, not Bordeaux mixture.
Copper sulphate with sulphur is not the standard Bordeaux formulation and lacks the lime component that buffers copper.
Step 4: Historical note and mode of action.
Discovered in the 1880s for downy mildew control in vineyards, Bordeaux mixture acts as a surface protectant releasing copper ions that inhibit spore germination.
Step 5: Conclusion.
Thus, Bordeaux mixture consists of copper sulphate and lime.

Step 1: Understanding DIPA.
DIPA stands for the Destructive Insects and Pests Act, 1914.
It was introduced to regulate the import and spread of destructive insects and pests in India.
Step 2: Key features.
- It came into force in 1914.
- It provided the legal control of insects that threatened Indian agriculture.
- It allowed restrictions on the import of plants, soil, and related materials.
Step 3: Checking the options.
- A: Wrong, no such authority exists.
- B: Correct, DIPA stands for Destructive Insects and Pests Act.
- C: Correct, came into force in 1914.
- D: Correct, provides legal control of insects.
Step 4: Conclusion.
Thus, the correct answer is B, C and D only.

Step 1: Understanding NPV.
NPV stands for Nuclear Polyhedrosis Virus, which is a type of Baculovirus. It specifically infects and kills insects, particularly at their larval stages.
Step 2: Target group.
NPV is highly effective against Lepidopteran larvae, such as Helicoverpa armigera, Spodoptera litura, and other caterpillars. These larvae cause severe damage to crops like cotton, pigeon pea, and vegetables.
Step 3: Checking options.
- Lepidopteran larvae → Correct, this is the main use of NPV.
- Dipteran larvae → Controlled by other biological agents, not NPV.
- Locust → Controlled using fungal pathogens, not NPV.
- Mosquitoes → Controlled using Bti (Bacillus thuringiensis israelensis), not NPV.
Step 4: Conclusion.
Thus, NPV is primarily used to control Lepidopteran larvae.

Step 1: Identify the disease.
Tristeza disease is one of the most destructive diseases of citrus worldwide. The word "Tristeza" means sadness in Spanish, referring to the decline of infected citrus trees.
Step 2: Causal organism.
The causal agent is Citrus tristeza virus (CTV), which belongs to the genus Closterovirus. It is a phloem-limited virus transmitted by aphids, mainly Toxoptera citricida.
Step 3: Checking the options.
- Bacteria: Wrong, citrus canker is bacterial, not tristeza.
- Fungus: Wrong, tristeza is not caused by fungi.
- Virus: Correct, Citrus tristeza virus is responsible.
- Mycoplasma: Wrong, phytoplasmas cause diseases like little leaf, not tristeza.
Step 4: Conclusion.
Hence, Tristeza disease in citrus is caused by a virus.