🎒 Stress-Tolerant Varieties and Resilient Crop Management

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

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Stress-Tolerant Varieties and Resilient Crop Management

Breeding for Climate Resilience

The development of stress-tolerant varieties is the most direct and accessible adaptation strategy for smallholder farmers. Breeding approaches combine:

• Conventional breeding: Selection from germplasm, hybridization, backcross breeding
• Molecular breeding: Marker-assisted selection (MAS), QTL mapping for stress tolerance genes
• Genomic selection: Using whole-genome information to predict performance
• Speed breeding: Controlled environments to complete 4–6 generations/year

Key traits targeted:

• Root architecture for drought and nutrient capture
• Membrane thermostability for heat tolerance
• Anaerobic germination and Sub1 gene for submergence
• Ion exclusion and compartmentalization for salinity

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Drought Tolerant Varieties

Rice

• Sahbhagi Dhan (DRR Dhan 42): Released by DRR (Directorate of Rice Research), Hyderabad; yield advantage 20–30% under drought compared to susceptible varieties; deep root system; adopted widely in Jharkhand, Odisha, WB
• DRR Dhan 44: Medium-duration drought tolerant; suitable for upland conditions
• Mechanistic basis: Deeper root system enables access to sub-soil moisture; osmotic adjustment maintains turgor

Wheat

• HI 8498 (Malav Shakti): Durum wheat; drought tolerant with good grain quality; suitable for central India
• GW 322: Gujarat wheat; tolerates terminal drought; early maturity allows escape
• Key traits: Deeper rooting, waxy leaf surface reducing transpiration, stay-green trait (delayed senescence)

Maize

• DHMH varieties (Drought and Heat Maize Hybrids): developed under CIMMYT-ICAR collaboration
• Stay-green trait: Maintains photosynthetic activity longer under stress → better grain filling
• Yield advantage: 15–25% over normal hybrids under moderate drought

Chickpea

• JG 14: Short-duration (95–100 days); escapes terminal drought; suitable for residual moisture areas
• JAKI 9218: Extra-early variety; 85–90 days; used in receding flood situations
• ICC 4958: Root architecture trait donor; used in breeding programs worldwide

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Submergence Tolerant Varieties

The Sub1 Gene

The Sub1A gene (from Oryza rufipogon) enables rice plants to tolerate complete submergence for 2 weeks by:

• Suppressing the "snorkelling response" (futile elongation)
• Maintaining carbohydrate reserves during submergence
• Enabling rapid recovery after de-submergence

Key Varieties

• Swarna Sub1: Most widely adopted; Swarna background with Sub1 gene; suitable for flood-prone Eastern India (WB, Odisha, Assam, Bihar)
• CR Dhan 500: Central Rice Research Institute (CRRI), Cuttack; medium-duration; Sub1 gene; adapted to coastal flood conditions
• Samba Mahsuri Sub1: Premium quality grain with submergence tolerance

Impact: An estimated 5 million farmers in South and Southeast Asia now grow Sub1 varieties; yield advantage of 1–3 tonnes/ha compared to susceptible varieties in submergence years

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Heat Tolerant Varieties

Wheat

• HI 8498 (Malav Shakti): Also heat-tolerant; high grain-filling rate under elevated temperatures
• K 307: Released from G.B. Pant University; tolerant of late terminal heat stress; stable yield under warming conditions
• Mechanism: Higher pollen viability at elevated temperatures; faster grain-filling rate compensates for shorter duration

Tomato

• Arka Rakshak (IIHR-Bangalore): Sets fruit at temperatures up to 40°C; pollen remains viable; suited for summer growing
• Mechanism: Higher pollen tube growth rate and ovule viability at high temperatures

Rice

• N22: Aus-type variety; known heat tolerance at flowering; used as donor parent in breeding programs
• Dhan Shakti: DRR; heat-tolerant; suitable for areas with rising night temperatures

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Salinity Tolerant Varieties

Rice

• Lunishree (Orissa): Developed for coastal saline soils; tolerates EC up to 8–10 dS/m
• CST 7-1: Central Soil Salinity Research Institute (CSSRI), Karnal; performs well on salt-affected soils
• Pokkali: Traditional Kerala variety; extreme salt tolerance (EC 15–20 dS/m); used as donor in breeding
• Mechanism: Salt exclusion at root level, compartmentalization of Na⁺ in vacuoles, osmotic adjustment

Wheat

• KRL 213: CSSRI, Karnal; for saline and sodic soils; tolerates EC up to 12 dS/m
• KRL 19: CSSRI; suitable for semi-arid saline belts

Other Crops

• Barley: Naturally more salt-tolerant than wheat; recommended for saline areas
• Sesbania (green manure): Tolerates waterlogging and moderate salinity; improves soil condition

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Flood-Tolerant Rice Adoption

Flood-prone areas of Eastern India (Odisha, Bihar, WB, Assam) have benefited most from Sub1 varieties:

• Swarna Sub1 adoption: >5 million ha in South and Southeast Asia
• Farmer income increase: ₹3,000–5,000/ha in submergence years
• Seed supply through government seed agencies and KVKs

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Crop Diversification for Resilience

Crop diversification replaces risk by spreading climate exposure:

• Maize for paddy in Punjab: Under Paani Bachao Paisa Kamao scheme; reduces groundwater extraction by 70% per ha; maize uses 40% less water than rice
• Pulses in rice fallow: Lentil, chickpea, blackgram in post-kharif residual moisture — no irrigation needed
• Oilseeds in wheat belt: Mustard intercropped with wheat for income diversification
• Horticultural crops: Higher value, shorter duration crops reduce exposure to single season failure

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Intercropping for Resilience

Cereal + legume intercropping provides stability across climate scenarios:

• Maize + cowpea; Sorghum + groundnut; Wheat + mustard
• Legume component can compensate if cereal fails (and vice versa)
• Nitrogen fixation by legume reduces fertilizer dependence
• Yield stability index: Intercropping systems show 15–30% more stable yields across variable years

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Cover Crops

Cover crops (non-harvested crops grown to protect and improve soil):

• Improve soil water holding capacity (SOM increase)
• Prevent erosion during off-season
• Build organic matter for long-term fertility
• Examples: Sesbania, Crotalaria, Oats, Rye

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Mulching for Resilience

Mulching modifies the microclimate at the soil-crop interface:

• Reduces soil temperature by 4–6°C during summer
• Conserves soil moisture (reduces evaporation by 30–50%)
• Suppresses weeds
• Types: Straw mulch (paddy straw, wheat straw), Plastic mulch (polyethylene), Legume mulch (living mulch)

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Crop Insurance as Adaptation

PMFBY (Pradhan Mantri Fasal Bima Yojana) provides climate risk management:

• Weather-based crop insurance covers yield losses from climate extremes
• Premium rates: 2% (Kharif), 1.5% (Rabi), 5% (commercial/horticultural crops)
• Government subsidy covers remaining premium
• Claims triggered by area-based yield below threshold or weather parameters

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Stress-Tolerant Varieties Summary Table

Crop	Variety	Institute	Stress	Yield Advantage
Rice	Sahbhagi Dhan	DRR, Hyderabad	Drought	+20–30% under drought
Rice	Swarna Sub1	IRRI/CRRI	Submergence	+1–3 t/ha in flood years
Rice	Lunishree	Odisha	Salinity	Stable yield at EC 8–10
Wheat	HI 8498	IARI, Indore	Drought+Heat	Stable under terminal stress
Wheat	KRL 213	CSSRI, Karnal	Salinity	Stable at EC 12 dS/m
Maize	DHMH hybrid	CIMMYT-ICAR	Drought+Heat	+15–25% under stress
Chickpea	JG 14	IIPR, Kanpur	Drought (escape)	Early maturity advantage
Tomato	Arka Rakshak	IIHR, Bangalore	Heat	Sets fruit at 40°C

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Key Terms

• Sub1 gene: Submergence tolerance gene from Oryza rufipogon; key to Swarna Sub1 success
• Stay-green trait: Delayed leaf senescence under stress; maintains grain filling
• Osmotic adjustment: Active accumulation of solutes to maintain turgor under drought
• PMFBY: Pradhan Mantri Fasal Bima Yojana — government crop insurance scheme
• Paani Bachao Paisa Kamao: Punjab scheme to shift from water-intensive rice to maize

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	ICAR-released stress-tolerant varieties for drought, submergence, heat, and salinity, plus crop management strategies for climate resilience.
Section context	Revise this lesson with the rest of Agronomic Interventions for stronger conceptual continuity.