Evaluation Of Drought Resistance And Physiological Regulation Mechanism Of Tall Fescue Genotypes

Drought stress is a major factor limiting turfgrass growth. Understandingmechanisms for drought resistance in turfgrass species is important for selecting andbreeding drought-tolerant cultivars and for water conservation in turfgrass management.The objectives of the dissertation research were1) to determine genetic variations inmajor physiological traits associated with drought tolerance in a collection of tall fescue(Festuca arundinacea) germplasms collected from different geographic regionsworldwide;2) to examine genetic diversity and relationship among germplasm varying indrought tolerance via molecular marker classification and physiological/biochemical traitanalysis; and3) to determine metabolic processes controlled by specific proteinsimparting superior drought tolerance in tall fescue using germplams contrasting indrought tolerance with high genetic diversity and through two-dimensionalelelctropheresis and mass spectrometry. These objectives were addressed by conductingfour independent experiments. The main results of different experiments are summarizedas the following:1Clustering analysis of different Tall Fescue genotypes for droughtresistancePlants of44accessions of tall fescue were exposed to well-watered conditions ordrought stress for13day. Visual evaluation of turf quality, leaf relative water content,electrolyte leakage, chlorophyll content, and evapotranspiration rate demonstrated widephenotypic variation contributing to drought tolerance in this collection of tall fescuegermplasm. A hierarchical cluster analysis was conducted based on physiological traitsand among44tall fescue accessions. Among the44accessions,12accessions wereclassified as most tolerant,17as moderately tolerant, and15as susceptible. Among the44accessions,‘SH-3-AM-US’from America and‘PI598949-EU-IT’from Europe were genetically distinct but both were classified as drought-tolerant germplasm based onphysiological data. These two accessions could be used as potential parents in breedingdrought-tolerant tall fescue genotypes.2Root antioxidant enzyme activities associated with drought tolerancein tall fescueTwo tall fescue genotypes ‘Focus’ and ‘PI150156’ contrasting in droughttolerance were examined in the greenhouse without irrigation for50days. Evaluation ofwhole-plant drought tolerance in different tall fescue genotypes was based on thevariations in turf quality (TQ) and leaf relative water content (RWC). Root physiologicaltraits, cell membrane stability (expressed as electrolyte leakage, EL), root viability (RV)and the activities of antioxidant enzymes, were determined to evaluate root activitiesassociated with drought tolerance. The results demonstrated that drought-tolerant traits ofleaves (TQ, RWC) were positively associated with root viability and superoxidedismutase (SOD) and catalase (CAT) activities while root membrane stability waspositively associated with root viability and activities of all four antioxidant enzymes(SOD, CAT, glutathione reductase and ascorbate peroxidase). This study suggested thatmaintaining high antioxidant enzyme activities of roots may help to maintain root cellmembrane integrity and root viability, and thus ultimately contribute to better droughttolerance of the whole plant.3Water use, photosynthetic traits and root development associatedwith drought resistance in tall fescue genotypesThe characteristics of water use, photosynthesis, and root morphological features androot viability were examined and compared among different genotypes of tall fescuediffering in drought tolerance. Plants of ‘Focus’, PI150156’,‘RU5’,‘RU7’,‘RU9’,‘RU10’,‘RU18’,‘RU19’, and ‘RU21’ were exposed to drought stress in greenhouse andcontrolled-environment growth chambers. The results demonstrated that the superior turfperformance (higher TQ) and leaf hydration status (higher RWC) under drought stresswere associated with sustained stomatal opening (greater stomatal aperature and stomatal conductance) and water use rate (higher transpiration rate, evapotranspiration rate andwater use efficiency) and maintaining higher photosynthetic rate (Pn), as well as thedevelopment of root system with higher viability (lower root EL) and higher ability ofextraction water. In addition, maintaining photosynthesis under long-term drought stressdepended on larger stomatal aperture, but not stomatal density. Higher specific rootlength or finer roots was positively related to the maintenance of higher TQ and RWC indrought-tolerant genotypes. This study suggested that the combined traits of developingfine (small diameter) and viable roots (lower EL) and leaves with higher stomatalopening are critical for controlling photosynthesis and water use under drought stressconditions.4. Identification of proteins associated with drought tolerance in tallfescueDrought tolerant‘RU9’and drought sensitive‘RU18’were exposed to droughtstress without irrigation for12days. The TQ, RWC, Pn, photochemical efficiency (Fv/Fm)of two tall feacue genotypes decreased, and EL increased under drought stress. Two-dimensional electrophoresis analysis identified31protein spots differentially expressedin the two genotypes under drought stress compared to their respective well-wateredcontrol plants. Mass spectrophotometry analysis revealed that differential expression ofproteins with functions controlling carbon fixation and glycolytic energy metabolismcould at least partially account for genotypic variations and contributes to superiordrought tolerance in tall fescue.