Assessment of plant hormone quantification as a new physiological trait
      for crop breeding using a new classification method for crop performance
      under drought
Creators: name: Thiry, Arnauld
Publisher: name: Lancaster University
Year: 2017
Subjects: Abiotic stress indices
Bread wheat
Crop breeding
Drought tolerance index
Productivity
Resilience
Scoring scale
Hormone balance
Hormones
Hormonal sensitivity
Hormonal signalling
Ethylene
Abscisic acid (ABA)
ABA/ETH
Genetic variation
Genotype × environment
Phenology
Phenological stages
Spike fertility
Leaf ethylene
Early selection
Field hormone quantification

description: The need to accelerate the selection of crop genotypes that are both
      resistant to and productive under abiotic stress is enhanced by global
      warming and the increase in demand for food by a growing world population.
      In this thesis, a new method is proposed for evaluation of wheat genotypes
      in terms of their resilience to stress and their production capacity. The
      method quantifies the components of the new index related with yield and
      yield components under abiotic stress. The index method, based on a
      scoring scale, offers a simple and easy visualization and identification
      of resilient, productive genotypes, according to their yield and yield
      components. This new selection method could help breeders and researchers
      by defining clear and strong criteria to identify genotypes with high
      resilience and high productivity and to reveal where genotypes express
      their susceptibility to a stress environment, providing a quantitative
      classification of contrasts in terms of yield and yield components.
      
      
      
      This index method has allowed 1) the identification of contrasting
      genotypes from a small population (CIMCOG-ROOT, 10 genotypes), and 2) the
      quantification of their contrasts, in terms of yield and yield components
      (grain number per spike), both constituting a key opportunity to test
      whether a stress hormone and/or hormone balance (ABA, ethylene and/or
      ABA/ethylene) could be used as a physiological trait for breeding for
      abiotic stress resilience. Due to the complexity of spatial and temporal
      variation of hormone accumulation (ABA and ethylene) and their different
      effects in plant development in response to stress environments, it is
      necessary to investigate how factors other than environment can influence
      the production of hormones. The factors considered in this work were: day
      time, water management (irrigation), tissue specificity (leaf and spike)
      and wheat phenological development (phenological stages).
      
      
      
      The present study of hormone (ABA and ethylene) quantification in wheat
      has shown that the genotypic variation in hormone signalling cannot be
      identified at every developmental stage of the plant. In fact, only two
      stages were identified for differences in ethylene emission (late- booting
      and heading), and two for ABA accumulation (late-booting and
      half-emergence), both on leaf tissue. However, the ratio ABA/ethylene
      (ABA/ETH) emerges as a better method to study genotypic variation in
      response to stress environments, in terms of hormone accumulation. In
      fact, both tissues, leaf and spike at all stages during the pre-anthesis
      stage (from booting to heading), have shown significant genotypic
      variation in terms of ABA/ETH balance.
      
      
      
      The resilience index of grain number per spike and this study of hormone
      (ABA and ethylene) quantification under drought stress (on leaf and
      spike), have shown that at late-booting stage, a lower leaf hormone ratio
      ABA/ETH and higher leaf ethylene emission is associated with a higher
      resilience of spike fertility (grain per spike resilience). However, under
      controlled conditions, a possible optimum threshold is observed in terms
      of leaf hormone ratio ABA/ETH. These results have been obtained with
      statistical significance in eight genotypes under field conditions and
      four genotypes under controlled environments.
      
      
      
      It is suggested in this work that a possible method for early selection of
      genotypes for high spike fertility resilience under drought stress could
      be developed by quantifying hormone signalling (leaf ethylene and the leaf
      ratio ABA/ETH at late-booting stage). However, some improvements in the
      process of hormone quantification need to be made before recommending this
      method to breeders.