Author(s)

Ramdeo Seepaul, Bisoondat Macoon, K. Raja Reddy, Brian Baldwin

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Cardinal temperatures for plant processes have been used for thermotolerance screening of geNotypes, geoclimatic adaptability determination and pheNological prediction. Current simulation models for switchgrass (Panicum virga-tum L.) utilize single cardinal temperatures across geNotypes for both vegetative and reproductive processes although intra-specific variation exists among geNotypes. An experiment was conducted to estimate the cardinal temperatures for seed germination of 14 diverse switchgrass geNotypes and to classify geNotypes for temperature tolerance. Strati-fied seeds of each geNotype were germinated at eight constant temperatures from 10^oC to 45^oC under a constant light intensity of 35 µmol m^-2 s^-1 for 12 h d^-1. Germination was recorded at 6-h intervals in all treatments. Maximum seed germination (MSG) and germination rate (GR), estimated by fitting Sigmoidal function to germination-time series data, varied among geNotypes. Quadratic and bilinear models best described the MSG and GR responses to temperature, respectively. The mean cardinal temperatures, T_min, T_opt and T_max, were 8.1, 26.6, and 45.1^oC for MSG and 11.1, 33.1, and 46.0^oC for GR, respectively. Cardinal temperatures for MSG and GR; however, varied significantly among geNotypes. GeNotypes were classified as sensitive (‘Cave-in-rock’, ‘Dacotah’, ‘Expresso’, ‘Forestburg’, ‘Kanlow’, ‘Sunburst’, ‘Trailblazer’, and ‘Warrior’), intermediate (‘Alamo’, ‘Blackwell’, ‘Carthage’, ‘Shawnee’, and ‘Shelter’) and tolerant (‘Summer’) to high temperature based on cumulative temperature response index (CTRI) estimated by summing individual response indices estimated from the MSG and GR cardinal temperatures. Similarly, geNotypes were also classified as sensitive (Alamo, Blackwell, Carthage, Dacotah, Shawnee, Shelter, and Summer), moderately sensitive (Cave-in-rock, Forestburg, Kanlow, Sunburst, and Warrior), moderately tolerant (Trailblazer), and tolerant (Expresso) to low temperatures. The cardinal temperature estimates would be useful to improve switchgrass models for field applications. Additionally, the identified cold- and heat-tolerant geNotypes can be selected for niche environments and in switchgrass breeding programs to develop new geNotypes for low and high temperature environments.

Switchgrass, Cardinal Temperature, Temperature Tolerance, Germination, GeNotype Variability, Response Index, Screening, GeNotype Classification

R. Seepaul, B. Macoon, K. Reddy and B. Baldwin, "Switchgrass (Panicum virgatum L.) Intraspecific Variation and Thermotolerance Classification Using in Vitro Seed Germination Assay," American Journal of Plant Sciences, Vol. 2 No. 2, 2011, pp. 134-147. doi: 10.4236/ajps.2011.22015.