BAI GIANG TAO GIONG NGO CHIU HAN docx

DROUGHT TOLERANCE IN MAIZE -THEORY & PRACTICE Pervez H. Zaidi Physiologist (VS), Maize Program, CIMMYT GLOBAL CLIMATE CHANGE & PROBLEM OF DROUGHT  Increased crop water requirement & use  Accelerated rates of crop growth & development  Reduced rate of transpiration & increased photosynthesis  More heat stress  Less stable weather  Major shift in weather pattern Impact on maize:  Frequent exposure to drought stress  Both win & loss situation, but unpredictable  Increase in yield in highlands  About 9-10% decline in yield in tropic  More severe decline (17%) in production in sub-Saharan Africa CHARACTERIZATION OF DROUGHT ENVIRONMENT Complex & far more difficult, because:  Global phenomenon with wide variability in degree, rather than kind  Tend to be distributed in a patchwork fashion round the world  Variation in intensity, severity & duration year-to-year and location-to- location Nevertheless, it is crucial for making decision & research planning Essential data sets:  Joint probability distribution index of water deficit in maize crop at different crop stages  Long-term data on weather pattern (rainfall, humidity, temperature, sunshine hours etc)  Detailed data on soil properties  Measure of the effects of water deficit on crop yield  Geographic distribution of maize planted by farmers APPROACHES TO DEFINE INCIDENCE & INTENSITY OF DROUGHT Approaches Reliability Reprodu -cibility Degree of quantification Cost 1. Expert opinion 2. Cluster analysis of monthly weather data 3. Cluster analysis + expert opinion 4. Cluster analysis of crop simulation results 5. Crop simulation results + expert opinion ** ** *** **** ***** * *** ** *** ** * ** *** ***** **** ** ** *** **** ***** Source : White & Elings (1997) DEFNITION OF DROUGHT FOR MAIZE CROP Based on rainfall: (Chapman & Baretto, 1996)  <500mm rainfall in lowland tropic and subtropical regions; <300-350mm in highlands - unsuitable area  <100mm rainfall received during four weeks bracketing flowering; unsuitable for maize crop - unsuitable area  100-200mm around flowering - marginal area  >500mm total rainfall & >200mm around flowering - suitable area Based on ratio of precipitation to evapotranspiration (P/PE)  P/PE >0.5 for during n (crop season) or more months - suitable area  P/PE >0.5 for n-1 or less months - marginal area  P/PE <0.5 during n-1 or more months – unsuitable area WATER RELATIONS  Solvent, cooling agent, reagent, maintenance of cell structure (cell turgor)  Water potential (ψ): * Measure of pressure needed for water extraction, unit- MPa (=10 bar). * Usually negative, indicating the status of water compared to full saturation * Water movement – from higher to lower WP i.e from less to more negative, e.g Soil (-0.35 MPa) –Plant (-4.5 MPa) -Atmosphere (-80 MPa), SPAC concept * Components : ψ = ψ p + ψ s + ψ m * Fully saturated leaf, ψ= 0 MPa, ψ p = +1.4 MPa. Ψ s = -1.4 MPa * At RWC 80% (20% water loss), ψ= -1.6 MPa, ψ p = 0 MPa (wilting), Ψ s = -1.6 MPa EVAPOTRANSPIRATION “Water losses due to evaporation from soil surface, non-stomatal water losses from plant & transpiration through stomata”  Largest proportion (>95%) by transpiration  Climatic factors: * Radiation - Major driving force * Temperature * Relative humidity (RH) * Wind  Plant factors : * Canopy architecture * Leaf area * Number & size of stomata  Grain yield determined by : GY = [W x P trans x WUE] x HI 1. Available Water (W)  Range : Field capacity (-0.03 MPa) to PWP (-1.5 MPa)  Available water to plants 55-65% between -0.03-0.5 MPa  Factors : i) Rainfall and irrigation, ii) Soil surface iii) Soil depth iv) Soil texture 2. Transpiration (P trans )  The proportion of water transpired by crop (>95% of total evapotranspiration)  Factors : i) Root length-density (1.0-1.5 cm/cm 3 below 50 cm soil depth) ii) Inter-crop & weeds iii) Plant growth rate at early stage Contd… WATER & PLANT GROWTH 3. Water use efficiency (WUE): i.e ratio between assimilation and transpiration. WUE = (P a -P i ) / {1.6 * (VP i -VP a )} where, P a = partial pressure of CO 2 in air P i = partial pressure of CO 2 inside leaf VP i = water vapor pressure inside leaf VP a = water vapor pressure in air  WUE is highest when- P i is low, VP a high, air temperature low, other growth factors are optimal  Genetic variability for WUE exists in maize (Hall et al., 1994) MAIZE UNDER DROUGHT STRESS (A)AT CELL LEVEL: i) Abscisic acid (ABA) : root-to-shoot signaling, ii) Inhibition of cell division & expansion iii) Osmoregulation : accumulation of osmolytes such as- sugar, proline, glycine, betain etc. help in reducing ψ s (more minus) facilitate water extraction from soil iv) Photo-oxidation of Chlorophyll: Affects PSII that produce super-oxide radicals, which causes photo-oxidation of chlorophyll (leaf bleaching symptoms) & thereby severe inhibition of photosynthesis. v) Reduced enzyme activity: e.g Rubisco, acid invertase, NR, NiR etc. (B) AT PLANT/CROP LEVEL : i) Poor seedling growth and establishment resulted poor plant stand ii) Leads reduced expansion of leaf>silk>stem>root>grain iii) Stomatal closure Contd… [...]... ability to maintain growth at low tissue water status (low ψ)  Prolificacy (avoidance) : to avoid putting all the eggs in one basket, selecting for more than one EPP, beneficial under stress conditions, no barrenness  High grain yield under drought (all mechanisms) : grand integration of all the favorable traits when plant is subjected to array of moisture stress circumstances SUSCEPTIBLE GROWTH STAGES... current photosynthates, not able to utilize stored assimilate  Reduced acid invertase activity in silk & developing kernel under drought make them more poorer sink  High susceptibility of kernel to enhanced ABA under drought, causes severe kernel abortion DROUGHT AND MAIZE PLANT Important considerations: Crop stage Susceptibility to stress Probability of stress Probability of breeding success 1 Early... indices (Falconer, 1981)  Comparison of near-isogenic lines differing for the trait of interest  Divergent selection within a population for the trait of interest  Analyzing the morpho-physiological changes in the trait in varieties selected for better performance under stress conditions  Simulation models IMPORTANT TRAITS FOR DROUGHT Traits Heritability under stress Relationship with yield Selection... Typically low frequency of the stress tolerance alleles in most of the maize germplasm  Stress tolerance based on two highly dynamic components, i.e.1) Maize plant : variability in response to drought changes with crop stage 2) Incidence of Drought : high uncertainty in Intensity/severity, year-to-year, location-to-location  Policy issues: In principle - high priority area, in practical - poor attention... introgression NEW BREEDING GERMPLASM i) Source germplasm ???  General adaptation: tropical, subtropical/mid-altitude, temperate  Grain texture/color  Maturity group on the basis of heat degree units (rather than calendar days)  Tolerance to biotic & abiotic stresses  Heterotic pattern & combining ability  Information about other value added traits On the basis of informations on these aspect, select & introduce . the eggs in one basket, selecting for more than one EPP, beneficial under stress conditions, no barrenness.  High grain yield under drought (all mechanisms) : grand integration of all the favorable. & far more difficult, because:  Global phenomenon with wide variability in degree, rather than kind  Tend to be distributed in a patchwork fashion round the world  Variation in intensity,. -THEORY & PRACTICE Pervez H. Zaidi Physiologist (VS), Maize Program, CIMMYT GLOBAL CLIMATE CHANGE & PROBLEM OF DROUGHT  Increased crop water requirement & use  Accelerated rates