Botany 2023 Paper I 50 marks Evaluate

Q3

(a) Define microbial biopesticides. What are their types? With suitable examples, evaluate the potential of microbial biopesticides in pest and disease control in crop plants. (20 marks) (b) Explain the general features of viroids. How do they differ from viruses? Name two diseases caused by virions. (15 marks) (c) Distinguish between the natural and phylogenetic systems of plant classification. Mention their merits and demerits. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) सूक्ष्मजीवी जैव कीटनाशक को परिभाषित कीजिए। ये कितने प्रकार के हैं? उपयुक्त उदाहरणों सहित, फसल के पौधों के कीट एवं रोग नियंत्रण में, सूक्ष्मजीवी जैव कीटनाशकों की क्षमता का मूल्यांकन कीजिए। (20 अंक) (b) वायरोइड के सामान्य लक्षणों की व्याख्या कीजिए। ये वाइरस से किस प्रकार भिन्न हैं? वायरियन से होने वाली दो बीमारियों के नाम बताइए। (15 अंक) (c) पौधों के वर्गीकरण की प्राकृतिक और जातिवृत्तीय प्रणाली में अंतर बताइए। इनके गुण और दोषों का उल्लेख कीजिए। (15 अंक)

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Approach

Begin with a concise definition of microbial biopesticides for part (a), then systematically cover types with Indian examples like Bacillus thuringiensis var. kurstaki and Trichoderma viride. Spend approximately 40% of word budget on (a) given its 20 marks, 30% each on (b) and (c). For (b), contrast viroids with viruses using a tabular format and cite Potato spindle tuber viroid and Coconut cadang-cadang. For (c), use comparative tables for natural (Bentham & Hooker) versus phylogenetic (APG IV, Cronquist) systems, concluding with why phylogenetic systems dominate modern taxonomy.

Key points expected

  • Part (a): Definition of microbial biopesticides as pest control agents derived from microorganisms (bacteria, fungi, viruses, protozoa, nematodes); classification into bacterial (Bt, Bacillus sphaericus), fungal (Beauveria bassiana, Metarhizium anisopliae, Trichoderma), viral (NPV, GV), and nematode-based biopesticides
  • Part (a): Evaluation of potential including specificity, safety to non-target organisms, reduced environmental persistence, resistance management, and limitations like narrow spectrum, slower action, and formulation challenges with Indian crop examples (cotton bollworm, rice stem borer, groundnut leaf spot)
  • Part (b): General features of viroids—small, circular, single-stranded RNA without protein coat, no mRNA activity, self-cleaving hammerhead ribozymes, nuclear or chloroplastic replication; structural differences from viruses (no capsid, no envelope, smaller genome, no encoded proteins)
  • Part (b): Two diseases caused by viroids—Potato spindle tuber disease (PSTVd) and Coconut cadang-cadang disease (CCCVd) or Citrus exocortis, with brief symptomatology
  • Part (c): Natural system (Bentham & Hooker, 1862-1883) based on morphological similarities and correlated characters; merits (practical, herbarium-friendly) and demerits (artificial groupings, evolutionary blindness)
  • Part (c): Phylogenetic system based on evolutionary relationships using molecular data (DNA sequences, cladistics); merits (reflects true relationships, predictive power) and demerits (instability, requires technical expertise); mention APG IV classification as contemporary standard

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Precise definitions across all parts: microbial biopesticides distinguished from biochemical pesticides; viroids correctly identified as subviral pathogens with hammerhead ribozyme mechanism; natural versus phylogenetic systems accurately characterized with correct historical attribution (Bentham-Hooker, APG IV)Generally correct definitions with minor errors—confusing biopesticides with biofertilizers, vague viroid description, or mixing up natural and phylogenetic system principlesFundamental conceptual errors—calling viroids as viruses, describing phylogenetic systems as solely morphological, or equating microbial biopesticides with synthetic pesticides
Diagram / labelling14%7Clear comparative table for viroids vs. viruses with structural diagrams; schematic representation of biopesticide mode of action (infection cycle); cladogram or flowchart showing progression from natural to phylogenetic classification; all diagrams properly labelled with scientific annotationsBasic tables without diagrams, or diagrams present but poorly labelled; missing visual elements for at least one sub-partNo diagrams or tables; entirely text-based response despite visual components being strongly implied by comparative questions
Examples & nomenclature20%10Specific Indian and international examples: Bt cotton (Cry1Ac, Cry2Ab), Trichoderma viride for groundnut, NPV for Helicoverpa; PSTVd and CCCVd with correct abbreviations; citation of Bentham & Hooker's Genera Plantarum, Cronquist, Takhtajan, and APG IV with approximate datesGeneric examples without strain specificity; one correct viroid disease but second incorrect or omitted; classification systems named without authors or datesIncorrect examples—citing bacteria for viroids, confusing classification authors, or using outdated/misattributed nomenclature throughout
Process explanation22%11Detailed mechanisms: biopesticide infection pathways (perforation, toxin production, competition); viroid replication via rolling circle mechanism and host RNA polymerase; evolutionary basis of phylogenetic classification using molecular synapomorphies and cladistic analysisSuperficial process description—stating biopesticides 'kill pests' without mode, or viroids 'multiply' without mechanism; basic mention of DNA sequencing for phylogenetic systemsNo mechanistic explanation; processes confused between categories (e.g., describing viral replication for viroids)
Application / ecology22%11Critical evaluation of biopesticide potential: IPM compatibility, organic farming suitability, resistance management advantages, and practical constraints (field persistence, cost, farmer adoption); ecological significance of viroids as molecular fossils and evolutionary models; synthesis of why phylogenetic systems enable conservation prioritization and predictive classificationUncritical listing of advantages without evaluation; missing ecological context for viroids; descriptive rather than analytical treatment of classification systems' applicationsNo evaluation component—purely descriptive; missing application context entirely; no connection to Indian agricultural or biodiversity conservation scenarios

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