Crop loss Study Guide

📖 Core Concepts Crop diversity (crop biodiversity) – the range of different crops, varieties, and their genetic/phenotypic traits grown in agriculture. Agricultural biodiversity – all living diversity in farming systems; crop diversity is a subset. Monoculture – planting a single crop variety over a large area; raises disease‑outbreak risk. Within‑crop diversity – genetic variation within a single crop species (e.g., many potato varieties). Genetic erosion – loss of genetic variation caused by selective breeding or uniform planting. Agroecosystem services – food, fuel, fibre, nutrient recycling, soil fertility, micro‑climate regulation, water regulation, pest control, waste detoxification. 📌 Must Remember Over the last 50 years, both genetic diversity within crops and the number of species cultivated have dropped sharply. Monoculture can enable a single disease to wipe out a whole harvest (e.g., Irish potato famine, Gros Michel banana loss). Food‑security risk: humanity now relies on a shrinking pool of crop varieties; loss of diversity = higher vulnerability. Biodiversity loss stats: up to 50 % of all plant species could go extinct if trends continue; 6 % of cereal wild relatives, 18 % of legume relatives, 13 % of Solanaceae relatives are already threatened. Genebank scale: CGIA‑R’s network stores > 778 000 accessions from > 3 000 crop/forage/agroforestry species. Bt corn → insecticidal toxin from Bacillus thuringiensis; protects target pests but can harm non‑target insects (e.g., monarch butterfly). 🔄 Key Processes Traditional crop rotation Year 1: Plant crop A (e.g., legumes) → fixes N, uses different nutrients. Year 2: Plant crop B (e.g., cereals) → benefits from residual N, breaks pest cycles. Modern plant breeding Identify desirable traits (yield, disease resistance, shelf life). Cross‑breed or use marker‑assisted selection → develop new variety. Side effect: reduces overall genetic variability (genetic erosion). Disease‑resistance strategy Deploy multi‑line cultivars (separate lines each carrying different resistance genes). Mix cultivars in the field → lowers probability that a single pathogen overcomes all defenses. 🔍 Key Comparisons Monoculture vs. Diverse Cropping Monoculture: uniform genetics → high disease susceptibility. Diverse cropping: multiple varieties/species → spreads risk, reduces pesticide need. Genebank Accessions vs. Commercial Varieties Genebank: broad genetic pool, many rare alleles, primarily for research/conservation. Commercial: high‑performing, narrow gene base, optimized for yield/market traits. Bt Corn vs. Conventional Corn Bt: built‑in insecticidal protein, lower pesticide sprays, possible non‑target impacts. Conventional: relies on external pesticide applications, no built‑in toxin. ⚠️ Common Misunderstandings “More varieties = lower yield.” Not always; diverse systems can maintain or even increase total productivity by reducing losses. “Genetic modification automatically saves biodiversity.” GM traits (e.g., Bt) reduce pesticide use but may still affect non‑target species; they don’t replace the need for genetic variation. “All crop diversity is the same as species diversity.” Diversity occurs at species, varietal, and genetic levels; each offers different ecological and economic benefits. 🧠 Mental Models / Intuition “Genetic safety net” – Think of each variety’s resistance genes as a net; the more strands (varieties), the less likely a single pest will fall through. “Biodiversity as insurance.” Just as an insurance policy spreads risk across many events, crop diversity spreads agricultural risk across many species/varieties. 🚩 Exceptions & Edge Cases Bt toxin specificity: Effective only against target insects; pests not susceptible remain a problem. Crop rotation limits: In very short‑term farming systems (e.g., intensive monoculture for cash crops), rotation may be impractical; other strategies (multi‑line mixes) become essential. 📍 When to Use Which Choose crop rotation when you have multiple years of land access and diverse market demands → maximizes soil health & pest break‑cycles. Select multi‑line cultivars for large‑scale monoculture fields where rotation isn’t feasible but disease pressure is high. Adopt GM traits (e.g., Bt) when specific pest pressure is severe, chemical pesticide use is restricted, and non‑target impact is acceptable. Utilize genebank material when breeding for new resistance genes or adapting to climate change; not for immediate commercial planting. 👀 Patterns to Recognize Disease outbreak + uniform crop → likely a monoculture‑related failure. Question mentioning “Gros Michel” or “Irish famine” → clue to discuss risks of low genetic diversity. Statistical percentages (6 %, 13 %, 18 %) → point toward threatened wild relatives → relevance to conservation/genebank importance. 🗂️ Exam Traps Distractor: “Crop diversity only matters for ecological services.” – Wrong; it also directly affects food security, economic risk management, and disease resistance. Near‑miss: “Bt corn eliminates all pesticide use.” – Incorrect; Bt reduces certain sprays but does not eliminate all pesticide applications and may have non‑target effects. Misleading choice: “Monoculture is always more profitable than diversified farming.” – Profitability depends on risk, market prices, and loss avoidance; diversity can yield higher long‑term returns. --- Use this guide to quickly recall the why, what, and how of crop diversity before the exam. Good luck!