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Jinyu Wang, Bo Yuan, Yi Xu and Bingru Huang

Amino acid and protein metabolism are interrelated and both play important roles in plant adaptation to heat stress. The objective of this study was to identify amino acids and soluble proteins associated with genetic variation in heat tolerance of hard fescue (Festuca trachyphylla). According to a previous screening experiment, the hard fescue cultivars Reliant IV and Predator were selected as heat-tolerant and heat-sensitive cultivars, respectively. Plants of these two hard fescue cultivars were exposed to heat stress at 38/33 °C (day/night) or optimal temperature at 21/18 °C in growth chambers. Each cultivar had four replications under each temperature, and the experimental design was a split-plot design, temperature as the main plots and cultivars as the subplots. Under heat stress, ‘Reliant IV’ exhibited higher turf quality (TQ) and greater membrane stability than ‘Predator’. In response to heat stress, total amino acid content increased, whereas total soluble protein content decreased in both cultivars. The greater accumulation of amino acids in ‘Reliant IV’ was contributed by the greater increase of proteins involved in the glycolysis and the tricarboxylic acid (TCA) cycle that provided carbon skeleton for amino acid synthesis. ‘Reliant IV’ leaves exhibited greater extent of increases in the content of six individual amino acids (histidine, glutamine, proline, threonine, aspartate, and tryptophan) than ‘Predator’ under heat stress. Several soluble proteins were upregulated in response to heat stress, to a greater extent in ‘Reliant IV’ than ‘Predator’, including the proteins involved in photosynthesis, protein folding, redox hemostasis, stress signaling, stress defense, cell organization, and metabolism. These differentially accumulated free amino acids and soluble proteins could be associated with the genetic variation in heat tolerance of hard fescue.

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Jinyu Wang, Patrick Burgess, Stacy A. Bonos, William A. Meyer and Bingru Huang

Summer decline is typically characterized by heat and drought stress and is a major concern for fine fescue species (Festuca). The objectives of this study were to examine whether heat or drought stress is more detrimental, and to determine the genotypic variations in heat and drought tolerance for fine fescues. A total of 26 cultivars, including seven hard fescues (Festuca trachyphylla), eight chewings fescues (Festuca rubra ssp. commutate), seven strong creeping red fescues (Festuca rubra ssp. rubra), two sheep fescues (Festuca ovina ssp. hirtula), and two slender creeping red fescues (Festuca rubra ssp. littoralis) were subjected to prolonged heat or drought stress in growth chambers. Several physiological parameters, including turf quality (TQ), electrolyte leakage (EL), photochemical efficiency (F v/F m) chlorophyll content (Chl), and relative water content (RWC) were measured in plants exposed to heat or drought stress. The results indicated that heat stress was more detrimental than drought stress for fine fescue species. Based on TQ and major physiological parameters (EL and F v/F m) under heat stress, several cultivars with good heat tolerance were selected, including ‘Blue Ray’, ‘Spartan II’, ‘MN-HD1’, ‘Shoreline’, ‘Navigator II’, ‘Azure’, ‘Beacon’, ‘Aurora Gold’, ‘Reliant IV’, ‘Marco Polo’, ‘Garnet’, ‘Wendy Jean’, ‘Razor’, and ‘Cindy Lou’. Based on TQ and major physiological parameters (EL, RWC, and F v/F m) under drought stress, several cultivars with good drought tolerance were selected, including ‘Spartan II’, ‘MN-HD1’, ‘Reliant IV’, ‘Garnet’, ‘Azure’, and ‘Aurora Gold’. These cultivars could be used in hot, dry, or both environments and as breeding germplasm for developing heat tolerance, drought tolerance, or both.