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Seminar ppt 2017 heat stress

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DOCTORAL SEMINAR- I

On

INFLUENCE OF HIGH TEMPERATURE AND BREEDING FOR HEAT TOLERANCE

Submitted by VITNOR SUSHIL SARJERAO

Reg. No. 015/14

Submitted to Dr. J. V. PATIL

Head,Department of Agricultural Botany

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Points to be covered:-

Introduction

Effects of high temperature

Heat stress and heat tolerance

Screening for heat tolerance traits

Breeding for high temperature tolerance

Summary and conclusion

Case Study

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1. Introduction

Heat stress is often defined as the rise in temperature beyond a threshold

level for a period of time sufficient to cause irreversible damage to plant

growth and development.

At very high temperatures, severe cellular injury and even cell death may

occur within minutes, which could be attributed to a catastrophic collapse of

cellular organization

Direct injuries due to high temperatures include protein denaturation and

aggregation, and increased fluidity of membrane lipids. Indirect or slower

heat injuries include inactivation of enzymes in chloroplast and

mitochondria, inhibition of protein synthesis, protein degradation and loss of

membrane integrity

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II. EFFCTS OF HIGH TEMPERATURE

A. Morphological and yield traits

At later stages, high temperature may adversely affect

photosynthesis, respiration, water relations and membrane

stability, and also modulate levels of hormones and

primary and secondary metabolites.B. Morphological symptoms

High temperatures can cause considerable pre and

postharvest damages, including scorching of leaves and

twigs, sunburns on leaves, branches and stems, leaf

senescence and abscission, shoot and root growth inhibition,

fruit discoloration and damage, and reduced yield

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B. Physiological and biochemical traits

1. Waters relations Under field conditions, high temperature stress is frequently associated with reduced water availability

2.Accumulation of compatible osmolytesA key adaptive mechanism in many plants grown under abiotic stresses, including salinity, water deficit and extreme temperatures, is accumulation of certain organic compounds of low molecular mass, generally referred to as compatible osmolytes3 PhotosynthesisAny constraint in photosynthesis can limit plant growth at high temperatures.4. Assimilate partitioningUnder low to moderate heat stress, a reduction in source and sink activities may occur leading to severe reductions in growth, economic yield and harvest index. Assimilate partitioning, taking place via apoplastic and symplastic pathways under high temperatures, has significant effects on transport and transfer processes in plants

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5. Cell membrane thermostability

Heat stress accelerates the kinetic energy and movement of

molecules across membranes thereby loosening chemical bonds

within molecules of biological membranes

6. Hormonal changes

Hormones play an important role in this regard. Cross-talk in

hormone signaling reflects an organism’s ability to integrate

different inputs and respond appropriately.

A gaseous hormone, ethylene regulates almost all growth and

developmental processes in plants, ranging from seed ger-

mination to flowering and fruiting as well as tolerance to

environmental stresses.

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III. HEAT STRESS AND HEAT TOLERANCE

A.Definition of Heat Stress

Heat stress is often defined as the rise in temperature beyond a threshold level for

a period of time sufficient to cause irreversible damage to plant growth and

development.

B. Heat Tolerance

The adverse effects of heat stress can be mitigated by developing crop plants with

improved thermotolerance using various genetic approaches

Tolerance to this stress via knowledge of metabolic pathways will help us in

engineering heat tolerant plants.

A group of proteins called heat shock proteins are synthesized following stress

and their synthesis is regulated by transcription factors.

Under high temperature (HT), reactive oxygen species (ROS) are often induced

and can cause damage to lipids, proteins, and nucleic acids.

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IV.SCREENING FOR HEAT TOLERANCE TRAITS

it is imperative to use cost efficient and reliable techniques to screen the

available germplasm for various ecophysiological, morphological, and

reproductive traits to assist their utilization in crop breeding programs.

A brief description of some new emerging ecological, morphological, and

physiological techniques, which are being used in many crop improvement

programs particularly at various international crop improvement centres

(mainly CIMMYT and IRRI) and other national research centres, are

discussed in this section.

However, these controlled environments can be used for preliminary screening

but it will be important to also test the performance of the genotypes identified

under controlled condition in field conditions before they are used extensively

in the breeding programs.

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PHYSIOLOGICAL AND/OR BIOCHEMICAL TRAITS1. Cellular Membrane Thermo stability High temperature modifies membrane composition and structure and can cause leakage of ions. Membrane disruption also causes the inhibition of processes such as photosynthesis and respiration. 2. Chlorophyll Content exhibited physiological evidence indicating that loss of chlorophyll during grain filling was associated with reduced yield in the field .They also established that while high chlorophyll content does not guarantee heat tolerance.3. Chlorophyll Fluorescence Chlorophyll fluorescence emission kinetics from plants provides an indicator of plant photosynthetic performance The sensitivity of chlorophyll fluorescence to perturbations, in metabolism coupled with the ease and speed of measuring chlorophyll fluorescence, makes fluorescence a potentially useful for non invasive screening to identify metabolic disturbances in leaves.

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4. Carbon Isotope Discrimination There are two naturally occurring stable isotopes of carbon, 12C and 13C As water becomes limiting, stomatal closure occurs, therefore, discrimination against 13C decreases as water stress increases be-cause the ratio of 13C:12C increases in stressed leaves of C3 plants, and Rubisco has less opportunity to discriminate The carbon isotope discrimination has not been used to study the effects of high temperature alone or in combination with water stress, despite the fact that heat stress is an important component of drought stressB. Ecophysiological Traits1. Aerodynamic Resistance If the canopy resistance to heat and water vapor diffusion is large, an increase in stomatal conductance would tend to cool and humidify the air in the boundary layer, thus lowering the leafair vapor pressure deficit (VPD); TE would then increase They observed maximum potential differences in evapotranspiration rates of 13%. The de-creased transpiration rate in the warmer environment should decrease the rate of water uptake from the profile and increase the period of water availability to the plant.

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2. Quantification of Stress Index Using Canopy Temperature Leaf, foliage, and canopy temperatures have excited plant physiologists

and atmospheric physicists alike for more than 100 years (Jackson, 1982). stated that plant temperature might be a valuable qualitative

index to differences in plant water regimes. In the last 25 years, there has been rapid development in the use of foliage temperature to quantify plant stress.

a. Canopy Temperature Depression. The difference between air and foliage temperature is referred to canopy

temperature depression (CTD). The ability of the plant to decrease temperature through transpiration cooling will keep the plant cool and benefits plants at above optimal stress conditions.

demonstrated that canopy temperature of field grown cotton tracked air ‐temperature at night and became cooler than air temperature each morning when the leaf temperature approached 27.5 C.

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b. Crop Water Stress Index.

Initially stress degree day (SDD) was Ehrler (1973) concluded that using leaf‐

air temperature differences for scheduling irrigations in cotton was useful.

demonstrated that the difference in leaf and air temperature of well irrigated ‐

cotton and wheat was linearly related to VPD of the atmosphere 1 m above the

crop canopy.

c. Thermal Stress Index.

These authors stressed that the impact of changing air temperature on plant

growth and performance can be understood only whenthe temperature providing

optimum enzyme function is known.

The temperature response curves for recovery of PSII fluorescence following

illumination compare favourably with the TKW in several crop species

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C. Association Among Ecophysiological, Morphological, and Yield Traits

reported a highly significant negative correlation (r2 ¼ 0.79) between fruiting

height and yield. Empirically the first fruiting nodes number has been associated

with earliness of a particular genotype.

Again earliness has been found to be negatively correlated with yield in Pima

cotton. Temperature is an important factor modulating the interrelationship(s) of

the above parameters. Bhardwaj and Singh (1991)

Higher temperature can have significant negative impact on photosynthesis,

reduced photosynthetic rates, and the modulation of other metabolic factors, in

association with lower light intensities, may result in lower micronaire, fibre

strength, and yield

The micronaire reading of fiber produced in the warmest environment was

highest (Quisenberry and Kohel, 1975).

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V. BREEDING FOR HIGH TEMPERATURE TOLERANCE ‐

a.Genetic improvement for heat-stress tolerance

These responses accommodate short-term reaction or tolerance to specific

stresses. However, genome plasticity in plants, including genetic (e.g., directed

mutation) and epigenetic (e.g., methylation, chromatin remodeling, histone

acetylation) changes, allows long-term adaptation to environ-mental

changes/conditions

However, information regarding the genetic basis of heat tolerance is generally

scarce, though the use of traditional plant breeding protocols and contemporary

molecular biological techniques, including molecular marker technology and

genetic transformation, have resulted in genetic characterization and/or

development of plants with improved heat tolerance.

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b. Conventional breeding strategies

Employing traditional breeding protocols to develop heat tolerant crop plants are

as follows:

1. Identification of genetic resources with heat tolerance attributes. In many

plant species, for example soybeans and tomatoes, limited genetic variations

exist within the cultivated species necessitating identification and use of wild

accessions. However, often there are great difficulties in both the identification

and successful use of wild accessions for stress tolerance breeding (Foolad,

2005).

2. When screening different genotypes (in particular wild accessions) for growth

under high temperatures, distinction must be made between heat tolerance and

growth potential. Often plants with higher growth potential perform better

regardless of the growing conditions.

3. When breeding for stress tolerance, often it is necessary that the derived

lines/cultivars be able to perform well under both stress and non-stress

conditions.

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A. TRAIT SELECTION emphasized that the selection of plants on a physiological and genetic basis will make it possible to get varieties and hybrids with high photosynthetic efficiency and a balanced ratio between source and sink that will provide the maximum expression of yield potential. Plant breeders can use photosynthetic rate as a selection criterion for improved lines. These improved lines in turn could be crossed with other lines that possess suitable partitioning of photosynthates between reproductive and vegetative growth B. Isogenic lines to study individual trait performance Ideally, several pairs of isogenic lines should be developed with different genetic backgrounds, because the agronomic value of a gene(s) can depend on the other genes present in the genome Understanding the relationship between traits and yield is being mediated by the identification and marking more of the controlling genes and their alleles.

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C. GENETIC VARIABILITY (1)presence of suffcient genetic variability in its expression, (2) the characters should be characterized genetically, (3) the character must be related to agronomic benefit (e.g., yield, aspects of quality, and production cost), and (4) it must be measurable in large scale trials. Therefore, in this section the results of various reports with regard to genetic variability of different ecomorpho physiological traits related to high temperature ‐tolerance are presented and discussed.This indicates that genes that allow the saprophyte to function at high temperatures also allow the pollen to retain fertility after heat stress.

D. INHERITANCE STUDIES It has been demonstrated that modifying membrane fluidity can influence gene expression reported that a soybean mutant deficient in fatty acid unsaturation showed strong tolerance to high temperature.the thylakoid membranes of two Arabidopsis mutants deficient in fatty acid unsaturation (fad 5 and 6) showed increased stability to high temperature.

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E. IMPACT OF HEAT TOLERANT GENES In cowpea, heat tolerant genes progressively enhanced

grain yield from first flush of flowers by increasing pod set on the main stem nodes, and enhancing the overall partitioning of carbohydrates into grain with increases in night time temperatures above 20 C

Heat tolerant genes (or closely linked genes) also had a progressive dwarfing effect, mainly resulting from shorter main stem internodes and involving reduced shoot biomass production at night temperatures above 15 C.

They concluded that heat tolerant (or associated) genes and the dwarfing and reduced biomass production associated with the heat tolerant genes could have negative effects in some environments.

Transgressive segregation toward higher relative injury values in progeny than in parents of wheat suggests that the parents contributed different genes for high temperature tolerance and the trait is not simply inherited

F. BREEDING FOR HIGH TEMPERATURE TOLERANCE The increase in productivity must be realized not by means of the vegetation

period but by activation of productive process by increased rate of photosynthesis combined with higher number of bolls, increased boll weight, and harvest index up to 50%

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(1) conventional breeding and germplasm selection, especially of wild relatives of a species;

(2) elucidation of the specific molecular control mechanisms in tolerant and sensitive genotypes;

(3) biotechnology oriented improvement of selection and breeding procedures ‐through functional genomics analysis, use of molecular probes and markers for selection among natural and bred populations, and transformation with specific genes; and

(4) improvement and adaptation of current agricultural practices.G. PRACTICAL ACHIEVEMENTS

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VI.SUMMARY AND CONCLUSIONS Heat stress due to increased temperature is an agricultural problem in many

areas in the world. Transitory or constantly high temperatures cause an array of morpho-

anatomical, physiological and biochemical changes in plants, which affect plant growth and development and may lead to a drastic reduction in economic yield.

In order to cope with heat stress, plants implement various mechanisms, including maintenance of membrane stability, scavenging of ROS, production of antioxidants, accumulation and adjustment of compatible solutes, induction of mitogen-activated protein kinase (MAPK) and calcium-dependent protein kinase (CDPK) cascades, and, most importantly, chaperone signaling and transcriptional activation.

However, information regarding the genetic basis of heat tolerance is generally scarce, though the use of traditional plant breeding protocols and contemporary molecular biological techniques, including molecular marker technology and genetic transformation, have resulted in genetic characterization and/or development of plants with improved heat tolerance. In particular, the application of quantitative trait locus (QTL) mapping has contributed to a better understanding of the genetic relationship among tolerances to different stresses.

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Case Study – I1. High temperature stress in cotton Gossypium hirsutum L.Jehanzeb Farooq1, Khalid Mahmood1, Muhammad Waseem akram2, Atiq UrRehman2, Muhammad Imran Javaid2, I. Valentin Petrescu-Mag3,4, BilalNawaz2Abstract:-Heat stress is among one of the limiting and ever looming threats to cotton productivity in Pakistan. This factor inflicted huge losses in the recent years. In Pakistan genotypes developed for general cultivation face very high temperature of about 50 °C during the month of June which is about 20 °C more than the optimum temperature thus retard yield to greater extent. The plant parts like buds, flowers, fiber quality traits are greatly influenced due to high temperature. This mini review partially covers effect of heat stress on cotton fiber quality, plant parts, screening procedures, genetics and biotechnological aspects related to heat stress. All the information provided in the manuscript will help to better understand the phenomena of heat stress tolerance thus will ultimately aid in the development of heat tolerant cultivars in Pakistan.Key words: Heat stress, cotton fiber, Pakistan, G. hirsutum, supra-optimal temperature.

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Case Study – II2. The tolerance of durum wheat to high temperatures during grain fillingB. Maçãs, M.C. Gomes, A.S. Dias and J. CoutinhoSUMMARY – In South Portugal, rising temperatures during spring can be considered an important factor limiting wheat yields. Heat stress assumes particular importance when the wheat crop is under irrigation, where high yield potential is needed. The main objective of this study is to evaluate, under field conditions, the response of some wheat genotypes facing high temperatures during and after anthesis. Nine durum and eight bread wheat genotypes were exposed to two different sowing dates: normal and late sowing, to assure high temperatures during and after anthesis, in 1997-1998 and 1998-1999. Grain yield and individual grain weight were significantly affected by temperature increase in 1997-1998 season. Genotype x sowing date interaction was not observed indicating that selection pressure must be applied to identify genotypes with better resistance/tolerance to heat stress.Key words: Durum wheat, heat stress, yield potential, grain filling.

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Case Study – III3. TERMINAL HEAT STRESS ADVERSELY AFFECTS CHICKPEA PRODUCTIVITY IN NORTHERN INDIA STRATEGIES TO IMPROVE THERMOTOLERANCE IN THE CROP UNDER CLIMATE CHANGEP.S. Basu , Masood Ali and S.K. Chaturvedi∗ABSTRACT:- Chickpea (Cicer arietinum L.) is a cool-season legume well adapted within temperature range of 30/150C (day maximum and night minimum) for optimum growth and pod filling. The northern plains of India once represented a potential production zone for chickpea due to long winter favouring high biomass production and pod filling. However, the crop in this region is now adversely affected by climatic change, showing a trend of increasing minimum night temperature more than that of maximum day temperature. The asymmetric pattern of temperature rise resulted in a warmer winter, less dew precipitation and heavy evapo-transpirational water loss. The crop often experiences abnormally high temperature (>350 C) and atmospheric drought during reproductive stage. The chickpea varieties are now gradually replaced by newly bred short duration varieties escaping terminal heat, or breeding for heat tolerance has been initiated to enhance productivity

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A large number of germplasm were physiologically characterized for thermo

tolerance and screening techniques developed based on membrane stability,

photosynthetic efficiency (quantum yield, ratio of variable to maximal

chlorophyll fluorescence Fv/Fm) and pollen germinability. The foliar resistance

was much higher (above 400 C) than reproductive component like pollen

germination (usually occurs below 350C). The fluorescence inductions kinetics

showed a large differences in fluorescence peaks and quenching pattern when

leaves pretreated at 20, 30 40 and 460C with an irreversible damage of

photosynthetic systems at 460C. Membrane stability was significantly

correlated (R2= 0.7) with quantum yield (Fv/Fm) and proved to be viable

screening technique for thermo tolerance combined with pollen germinability at

high temperatures.

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Case Study – IV4. Screening wheat germplasm for heat tolerance at terminal growth stageAziz ur Rehman, Imran Habib, Nadeem Ahmad, Mumtaz Hussain, M. Arif Khan, Jehanzeb Farooq and Muammad Amjad Ali*Abstract:-The germplasm comprising of 442 wheat varieties/lines was sown in one meter long row in a plastic sheet tunnel to screen the material for heat tolerance during 2004-05 and 2005-06 at Wheat Research Institute, Faisalabad. A set of the material was sown in the open adjacent to the tunnel. The material was exposed to heat shock (>320C) by covering the tunnel with plastic sheet during grain formation for two weeks in 2004-05 and for four weeks in 2005-06. Data was recorded from 25 randomly selected heads from each row for 1000 grain weight, grains per spike and yield per spike during both the years. The data regarding survival (ability to stay green under heat stress) was also recorded. Heat effect was expressed as ratio of stressed / non stressed plants. The effects of heat stress were lesser in shorter period exposure and more drastic in prolonged exposure of the genotypes to heat. The ability of lines to stay green for longer period in heat shock had no direct relationship with seed setting.

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Three entries CB-367 (BB#2/ PT// CC/ INIA /3/ ALD’S’) CB-333 (WL

711/3/KAL/BB//ALD ‘S’) and CB-335 (WL711/CROW ‘S’//ALD#1/CMH77A.

917/3/HI 666/PVN ‘S’ ) showed maximum grain development and survival. This

study revealed that these genotypes can be utilized in breeding programs for

development of wheat varieties having heat tolerance at terminal growth stage.

Keywords: Bread wheat; Germplasm; Tunnel; Heat stress; Survival

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Case Study – IV5. Effect of heat stress on proline, chlorophyll content, heat shock proteins and antioxidant enzyme activity in sorghum (Sorghum bicolor) at seedlings stageG U Gosavi, A S Jadhav*, A A Kale, S R Gadakh, B D Pawar and V P Chimote Abstract:- The effect of heat stress on various biochemical and physiological parameters at seedling stage was investigated in drought tolerant, susceptible and wild sorghum [Sorghum bicolour (L.) Moench] genotypes. Under heat stress, susceptible genotypes showed higher reduction in total chlorophyll content than tolerant genotypes. Significant increase in proline accumulation and activities of d-1-pyrroline-5-carboxylate synthetase (P5CS), superoxide dismutase (SOD), peroxidise (POD) and catalase (CAT) enzymes were observed in stressed seedlings over control. Higher activities of antioxidant enzymes under stress condition might be useful for sorghum seedlings to cope up with oxidative damage by heat stress. Higher proline accumulation and antioxidant activities were observed in wild sorghum genotypes and could be used for gene mining for heat stress tolerance as well as in breeding programmes for transfer of heat stress tolerance trait

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. Many novel heat shock proteins (Hsps) were synthesized in drought tolerant

genotypes (19), followed by wild genotypes (8) and drought susceptible

genotypes (6). Thus, the above parameters studied would be useful as selection

criteria in identifying heat stress tolerant donors in future sorghum breeding

programmes. Pooled data from both RAPD and SSR analysis when subjected

to clustering analysis revealed wide divergence in wild genotypes for stress

resistant, while susceptible genotypes exhibited low divergence.

Keywords: Antioxidant enzymes, chlorophyll, heat stress, HSP, proline,

sorghum

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