MP Board · Class 9 · Science · Improvement in Food ResourcesAnswer the following comprehensive questions regarding Crop Variety Improvement and Protection Management: Explain six major objectives for which crop variety improvement (plant breeding) is carried out. Describe the three distinct modes by which insect pests attack crop plants, and state how they affect agricultural yield. Outline three effective methods (mechanical, chemical, and agronomic) used for controlling weeds in agricultural fields.

1. Objectives of Crop Variety Improvement\nCrop variety improvement is accomplished through plant breeding, selection, and hybridization to develop crops with desirable traits:

• Higher Yield: To increase the overall productivity of crops per acre of land.
• Improved Quality: Quality considerations vary from crop to crop. For instance, baking quality in wheat, protein content in pulses, oil quality in oilseeds, and preserving quality in fruits and vegetables.
• Biotic and Abiotic Resistance: Developing crop varieties resistant to biotic stresses (diseases, insects, nematodes) and abiotic stresses (drought, salinity, waterlogging, heat, and cold frost).
• Change in Maturity Duration: Shortening the time from sowing to harvesting enables farmers to grow multiple crops in a single year and reduces overall production costs.
• Wider Adaptability: Developing varieties that can grow under varied environmental conditions across different geographical regions.
• Desirable Agronomic Characteristics: Developing tallness and profuse branching for fodder crops, and dwarfness for cereal crops (so that fewer nutrients are consumed by plants for vegetative growth).

2. Modes of Insect Pest Attack\nInsect pests attack crop plants in three distinct ways, severely affecting plant health and decreasing total yield:

1. Chewing Insects: They cut and chew roots, stems, and leaves of the plants (e.g., grasshoppers, caterpillars). This reduces the photosynthetic area of leaves.
2. Sucking Insects: They pierce the plant tissues and suck cell sap from various plant parts (e.g., aphids, leafhoppers). This weakens the plant and leads to wilting and yellowing.
3. Boring Insects: They bore into stems, roots, or fruits/grains (e.g., sugarcane borer, pod borers), destroying internal tissues and making fruits unmarketable.

3. Methods of Weed Control\nWeeds are unwanted plants that compete with crop plants for light, water, space, and nutrients (e.g., Xanthium, Parthenium, Cyperus).

• Mechanical Methods: Physical removal of weeds by hand-uprooting, weeding with a trowel (khurpi), or plowing fields before sowing to uproot weeds.
• Chemical Methods: Spraying selective chemical weedicides/herbicides such as 2,4-D or Atrazine to selectively kill weeds without harming crops.
• Agronomic/Preventive Practices: Practices such as timely sowing of crops, proper seedbed preparation, intercropping, and crop rotation reduce weed infestation naturally.