Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Heat tolerance in wheat

2,548 views

Published on

Heat tolerance in wheat

Published in: Education

Heat tolerance in wheat

  1. 1. RAJASTHAN COLLEGE OFAGRICULTURE UDAIPUR (RAJASTHAN) Department of Plant Breeding and Genetics Dev Hingra Ph. D Scholar Mail Id- mail2devhingra@gmail.com
  2. 2. INTRODUCTION  Wheat (Triticum aestivum L.) is one of the world’s leading cereal crop.  In India wheat is the Second most important winter cereal after rice.  Bread wheat contributes approximately 95% to total production. Remaining 4% from durum wheat and 1% from Dicoccum.  India is the second largest producer of wheat in the world and the area and production during year 2013-14 recorded was Area (m. ha.) Production m. tonnes India 31.34 95.91 Rajasthan 2.81 8.92 (Anonymous, 2014a).
  3. 3.  Wheat is a thermo sensitive crop mostly grown in temperate environment. However, it is predominantly consumed in tropical and subtropical regions of the world. In subtropical regions it is cultivated in winter season but it exposed to high temperature stress at the end of the season i.e at grain filling stage. Heat stress is one of the major limiting factors for growth and productivity in wheat crop particularly in warmer region. Exposure to higher than normal temperature or heat stress reduces yield and decreases quality. Hence, now breeding for heat tolerance has become an integral component of wheat improvement at both National and International level.
  4. 4.  Temperature is basic to life processes, which increase with temperature within a limited range. This effect is expressed as Q10, which is the ratio of the rate at one temperature to that at a temperature 10°C lower.  When the temperature rises beyond the upper limit of the range, i.e., it goes above the optimal temperature, the relation between life processes and temperature is disturbed. Similarly, when the temperature goes below a threshold, which is often close to zero, life processes are disturbed enough to cause injury and death in sensitive genotypes. Heat stress
  5. 5. •Each plant species, more particularly each genotype, has an optimum range of temperatures for its normal growth and development, the specific temperatures would depend not only on the genotype but also on the stage of growth and development of a given genotype. When temperature moves beyond this optimal range, it generates temperature stress.
  6. 6. Heat-stress threshold It is a value of daily mean temperature at which a detectable reduction in growth begins / the temperature at which growth and development of plant cease. • Upper threshold: is the temperature above which growth and development cease. • Lower threshold (base temperature): is the temperature below which plant growth and development stop. • Cool season and temperate crops often have lower threshold temperature values compared to tropical crops.
  7. 7. Crop plants Threshold temperature (0C) Growth stage References Wheat 26 Post -anthesis Stone and Nicolas (1994) Corn 38 Grain filling Thompson (1986) Cotton 45 Reproductive Rehman et al., (2004) Pearl millet 35 Seedling Ashraf and Hafeez (2004) Tomato 30 Emergence Camejo et al., (2005) Brassica 29 Flowering Morrison Stewart (2002) Cool season pluses 25 Flowering Siddique et al., (1999) Ground nut 34 Pollen production Vara Prasad et al., (2000) Cow Pea 41 Flowering Patel and Hall (1990) Rice 34 Grain yield Morita et al., (2004) Threshold high temperatures for some crops plants
  8. 8. Research findings of ICAR ( Indian Council for Agricultural Research) on wheat crop has indicated that there is about 3 to 4 per cent decrease in grain yield with 1 degree Celsius rise in temperature during grain filling stage. Out of 28 million hectare area under wheat in India, about 9 million hectare in North Eastern plain zone, Central zone and peninsular zone is prone to terminal heat stress. Heat stress due to increased temperature is a very important problem globally
  9. 9.  The adverse effects on plants of temperatures higher than the optimal is considered as heat stress. Heat stress is an increased temperature level sufficient to cause irreversible damage to plant growth and development.  Occasional or prolonged high temperatures cause different Morpho-anatomical, physiological and biochemical changes in plants.  The ultimate effect is on plant growth as well as development and reduced yield and quality.  Generally a temperature rise, above usually 10 to 15°C above ambient, can be considered heat shock or heat stress.  Breeding for heat stress tolerance can be mitigated by breeding plant varieties that have improved levels of thermo-tolerance using different conventional or advanced genetic tools.
  10. 10. Heat would effect on Survival Cell and tissue survival Physiological effects Respiration Photosynthesis Photosynthate translocation Protein denaturation Membrane composition and stability Heat shock proteins Growth and devlopment Singh B.D.2014 Physiological Effects
  11. 11.  HSP is a group of proteins that normally exist in cells, but their synthesis is accelerated by heat.  Most of the stress proteins are soluble in water and therefore contribute to stress tolerance presumably via hydration of cellular structures.  In higher plants, HSPs is usually induced under heat shock at any stage of development. Heat shock proteins Proteinclass Size(kDa) Location HSP100 100-114 cytoplasm HSP90 80-94 cytoplasm,ER HSP70 69-71 ER,cytoplasm,mitochondria HSP60 10-60 chloroplasts,mitochondria smHSP 15-30 cytoplasm,chloroplast,ER,mitochondria Momamad and Whabi 2011
  12. 12. PLANT RESPONSES TO HEAT STRESS shoot and root growth inhibition scorching of leaves and twigs  sunburns on leaves branches and stems Leaf senescence and abscission fruit discoloration and damage and reduced yield • Reproductive phases most sensitive to high temperature are gametogenesis (8–9 days before anthesis) and fertilization (1–3 days after anthesis) in various crop plants (Foolad, 2005). • In wheat, both grain weight and grain number appeared to be sensitive to heat stress, as the number of grains per ear at maturity declined with increasing temperature (Ferris et al., 1998). Morphological symptoms
  13. 13.  Anatomical changes : At the whole plant level  Reduced cell size  Closure of stomata and curtailed water loss  Increased stomatal and trichomatous density  Greater xylem vessels of both root and shoot  Damaged the mesophyll cells and increased permeability of plasma membrane  High temperatures reduced photosynthesis by changing the structural organization of thylakoids  Loss of grana stacking or its swelling The cumulative effects of all these changes under high temperature stress may result in poor plant growth and productivity. Karim et al., 1997).
  14. 14. Measurement of heat tolerance parameters  Different physiological mechanisms may contribute to heat tolerance in the field— for example, heat tolerant metabolism as indicated by higher photosynthetic rates, stay-green, and membrane thermo-stability, or heat avoidance as indicated by canopy temperature depression. Several physiological and morphological traits have been evaluated for heat tolerance - Canopy temperature, leaf chlorophyll, stay green, leaf conductance, spike number, biomass, and flowering date.  Canopy temperature depression (CTD): There is a clear association of CTD with yield in both warm and temperature environments. CTD has been used as seletion criteria for tolerance to high temperature in wheat ( Munjal and Rana, 2001) reported that lower canopy temperature during grain filling period is an important physiological principle for high temperature stress tolerance. Indicating that the trait is heritable and therefore amenable to early generation selection. .
  15. 15.  CTD measurements were made by infrared thermometer which was focused to 10:1 meter and at the morning to early afternoon cloudless periods. Measurements were taken at three different growth stages ( pre anthesis, anthesis and post anthesis) Canopy temperature depression = air temperature – canopy temperature.
  16. 16.  Membrane thermo-stability:  Heat tolerance usually improves membrane stability under heat stress. Membrane stability may be determined as  (1) lipid fluidity. Lipid fluidity reaches at a temperature equal to 100c higher in heat-hardened plant then in unhardened plant.  (2) Electrolyte leakage. It is measured by conductometrically from leaf tissue segments taken from properly heat hardened plants subjected to a period of heat exposure.
  17. 17.  Chlorophyll content and stay green Chlorophyll content and stay green traits have been found to be associated with heat stress tolerance.  Photosynthesis: Declined photosynthesis is suggested as measure of heat stress sensitivity in plants.  Stem reserve remobilization : In cereals , this seems to be an important component of grain yield under heat stress.  Osmoregulation: osmoregulators like proline and glycine-betaine may have a protective role in heat stress.
  18. 18.  Stomatal conductance: A porometer was used to measure stomatal conductance across the upper and lower side of the leaf. It works by creating a seal on the leaf surface and actively pumping the air and moisture from the chamber. By doing so it is able to calculate a conductance rate across the leaf. The SPAD chlorophyll meter is also shown above and calculates an indexed value of chlorophyll content when a leaf is inserted between the sensors. Figure. Left- The model of Porometer used to calculate stomatal conductance. Right- A SPAD 502 chlorophyll meter used to measure leaf chlorophyll content.
  19. 19. Breeding approaches for heat tolerance  Introduction  Selection (ex. IC 29007A, IC 321889)  Mutation-  Hybridization Interspacific e.g.- C-306, Raj-3765, PBW-343, Raj-4037,HD-2935  Genetic engineering Garg et al 2012
  20. 20. Mechanisms  Heat stress resistance may be defined as ability of some genotypes to perform better than others when they are subjected to the same level of heat stress.  The various mechanisms of heat resistance may be grouped into two categories : (1) heat avoidance (2) heat tolerance  Heat avoidance : The ability of a genotype to dissipate the radiation energy and there by , to avoid a rise in plant temperature to a stress level. The primary mechanism of energy dissipation is transpiration.  Heat tolerance: Ability of some genotypes to withstand / perform better than others when their internal temperatures are comparable and in the realm of heat stress.
  21. 21. Selection environment for heat tolerance  Selection for heat tolerance can be carried out under the following four types of environment 1. Normal field environment : The natural field environment is the simplest and cheapest to use but its effectiveness depends mainly on the repeatability of the heat stress profile over years, and on the nature of heat tolerance being selected for it is unsuitable for the selection of such traits , which require a critical temperature. when the critical temperature is reached in the field, all the plants at the specific development stage, i.e., antheis may be marked by, say, a paint spray. Only the marked plants are evaluated at maturity, and the remaining population is regarded as escapes.
  22. 22. 2.Abnormal field environments : When normal field environment does not provide the suitable heat stress conditions, abnormal field environments available at certain locations or during the off- season may be used. e.g., wheat is grown during summer, which is the off- season.
  23. 23. 3.Programmed environments : such environments are available either in growth chambers or in green houses. The temperature programme should be such that the plants are subjected to appropriate heat hardening before their heat tolerance is evaluated. 4. In vitro environments : certain assays for heat tolerance can be performed in test tubes, e.g., membrane thermostabilty by the electro conductivity method.
  24. 24. SELECTION CRITERIA FOR HEAT RESISTANCE Yield under heat stress Growth under heat stress Recovery after heat stress Sensitivity of the photosynthetic process Flower formation and pollen fertility Seed germination under heat stress
  25. 25. Characteristic Measured As Usefulness As Selection Criterion Germination Percent germination under stress Useful when crop faces heat stress at germination Growth during heat stress Yield , biomass Most commonly used selection criterion Membrane stability Solute leakage (con-ductivity) Reasonable correlation ( r= .07) with yield under heat stress or with drought resistance Photosynthesis sensivity Chlorophyll fluorescence at 685 nm Becoming increasingly important : difficult to assay and , especially , interpret Recovery after heat stress Yield , biomass etc. Used whenever relevant for the target environment Sensitivity of reproductive phase Pollen fertility , grain filling Useful selection criterion ; accounted for in selection based on yield under heat stress Different selection criteria for heat tolerance DWR( 2009-10)
  26. 26.  Heat stress at late growth stages is a problem in 40% of wheat areas in the temperate environnent (Reynolds et al., 2001).  Grain weight is affected by high temperatures, especially those above 34 ºC, that reduce the duration of grain filling owing to the limited photosynthesis (Al Khatip and Paulsen, 1984), and inhibit starch biosynthesis in the endosperm (Keeling et al., 1993; Jenner, 1994).  Heat stress during post-anthesis (grain-filling stage) affects availability and translocation of photosynthates to the developing kernels and starch synthesis and deposition within the kernel, thus resulting in lower grain weight and altered grain quality (Bhullar and Jenner, 1985, Mohammadi et al., 2004). It has been observed that each degree rise in ambient temperature reduces the yield by 3-4% (Mishra, 2007).  The period from onset of spike initiation to flowering in wheat is very sensitive to temperature, and acceleration of this phase seems to be the main cause of yield reduction under hot conditions. Research findings
  27. 27. Work done in heat stress breeding  Wheat Variety Golden Halna (K0424 ) is a terminal heat tolerant variety developed by Wheat breeder Dr. L.P. Tiwari and others CSAUA&T, Kanpur.  It has tolerance up to 36 °C with yield potential of 40-45 quintal / ha. It matures in 90-110 days. The grain colour of this variety is golden bright and contains 12 to 12.5 % proteins. Good for Chapati making, it is found suitable for central and western part of U.P.( ICAR , 2012).  Heat tolerant varieties like DBW 14, DBW 16, Raj 3765, Lok 1, GW 322, Parbhani - 51, PBW – 373 are popular in India. DBW 16
  28. 28.  Attempts have been made to induce heat tolerance in a range of plant species using different approaches. -preconditioning of plants to heat stress -exogenous applications of osmo protectants or plant growth- regulating compounds on seeds or whole plants.  Physiological mechanisms of heat tolerance are relatively well understood, further studies are essential to determine. -physiological basis of assimilate partitioning from source to sink, plant phenotypic flexibility which leads to heat tolerance, -factors that modulate plant heat-stress response. -an understanding of root responses to heat stress, -most likely involving root–shoot signaling, is crucial and warrants further exploration. future prospects
  29. 29.  Molecular knowledge of response and tolerance mechanisms will give the way for engineering plants that can tolerate heat stress and could be the basis for production of crops which can produce economic yield under heat-stress conditions.

×