(a) Describe the causal organisms, disease cycle and control measures of Early Blight of Potato and Blast of Rice. 10+10=20

(b) What are eusporangiate and leptosporangiate sporangia ? Classify the sori based on the mode of development of sporangia i

Question

(a) Describe the causal organisms, disease cycle and control measures of Early Blight of Potato and Blast of Rice. 10+10=20

(b) What are eusporangiate and leptosporangiate sporangia ? Classify the sori based on the mode of development of sporangia in ferns, with suitable illustrations. 5+10=15

(c) Give an account of structural variation in the megasporophylls of different Cycas species with illustrations. Add a brief note on the primitive features in Cycas. 10+5=15

UPSC Answer Check · Accepted Answer

The directive 'describe' demands comprehensive, structured coverage of causal agents, disease cycles, morphological features and structural variations. Allocate approximately 40% of time/words to part (a) given its 20 marks, with 30% each to parts (b) and (c). Structure as: brief introduction → systematic treatment of each sub-part with integrated diagrams → concluding synthesis on evolutionary significance of primitive features in Cycas.
- Part (a): Causal organisms — Alternaria solani (Early Blight) with conidial morphology; Magnaporthe oryzae/Pyricularia oryzae (Blast) with pyriform conidia and appressorium formation
- Part (a): Disease cycles — primary and secondary infection sources, overwintering/survival structures, dispersal mechanisms and environmental triggers for both diseases
- Part (a): Control measures — cultural (crop rotation, resistant varieties like Kufri Jyoti), chemical (mancozeb, carbendazim), biological (Trichoderma) and integrated management
- Part (b): Eusporangiate vs leptosporangiate — developmental origin from multiple surface cells vs single superficial cell, sporangial wall layers, annulus presence and stomium structure
- Part (b): Sorus classification — eusporangiate types (coenosori, synangia) in Marattia, Danaea; leptosporangiate types (simple, compound, mixed, covered/indusiate) in Polypodiaceae, Dryopteris
- Part (c): Megasporophyll variation — C. circinalis (broad pinnate with distinct ovules), C. revoluta (narrower with more ovules), C. beddomei (compact with overlapping scales), C. rumphii (intermediate forms)
- Part (c): Primitive features — motile sperms with flagella, ovule structure resembling megasporangium, absence of pollen tube, circinate vernation, and retention of fern-like leaf morphology

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	20%	10	Accurately identifies Alternaria solani and Magnaporthe oryzae with correct teleomorph/anamorph relationships; precisely defines eusporangiate/leptosporangiate development; correctly describes megasporophyll homology with foliage leaves in Cycas	Identifies pathogens correctly but confuses teleomorph names or conidial details; basic distinction between sporangial types but misses developmental nuances; lists Cycas features with minor errors in homology interpretation	Misidentifies causal organisms (e.g., Phytophthora for Early Blight); conflates eusporangiate and leptosporangiate; fundamental errors in megasporophyll structure or primitive feature identification
Diagram / labelling	20%	10	Clear, scaled diagrams: conidia and disease cycle for (a); TS/LS of both sporangial types with annulus/stomium for (b); megasporophyll variations with ovule details for (c); all fully labelled with anatomical precision	Diagrams present but lacking scale or detail; sporangial diagrams miss annulus differentiation; megasporophyll drawings generic without species-specific variation; adequate but incomplete labelling	Absent or schematic diagrams only; no attempt at sporangial developmental stages; megasporophyll confused with microscopyll; poor or missing labels
Examples & nomenclature	20%	10	Cites specific resistant varieties (Kufri Jyoti, IR64); names representative genera for each sorus type (Marattia, Osmunda, Pteridium, Adiantum); specifies Cycas species with geographic distribution (C. beddomei — Eastern Ghats)	Mentions common varieties without specificity; lists some fern genera but misassigns to categories; knows C. circinalis and C. revoluta only; acceptable but limited nomenclatural precision	No specific varieties named; confuses fern families with sporangial types; single Cycas species mentioned; outdated or incorrect scientific names throughout
Process explanation	20%	10	Detailed disease cycle with infection court, incubation period, lesion development and spore dissemination; clear developmental sequence from sporangial initials to dehiscence; evolutionary progression from megasporangium to ovule with developmental homology	Basic disease cycle stages described; sporangial development in correct sequence but lacking cellular detail; megasporophyll development mentioned without evolutionary context; adequate but superficial process coverage	Confused or circular disease cycles; no developmental sequence for sporangia; megasporophyll described as static structure without developmental or evolutionary perspective
Application / ecology	20%	10	Integrated pest management approach for both diseases with economic thresholds; ecological significance of sporangial types in habitat adaptation (eusporangiate in shaded, leptosporangiate in open); biogeographic and conservation context of Cycas speciation in India	Lists control measures without integration; mentions habitat preferences for ferns; notes Cycas as living fossil without elaboration; limited applied or ecological perspective	Only chemical control mentioned; no ecological context for sporangial diversity; no mention of conservation status or evolutionary significance of Cycas

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