2.2 Plant materials and treatments
Seeds of two Tibetan wild barley accessions XZ29 (Al-tolerant) and XZ9 (Al-sensitive) (Cai et al., 2013), and a cultivar Dayton (Al-tolerant) were soaked in deionized water for 6 h at 20 °C in the dark and then germinated on moist filter papers in an incubator (20/14 °C, day/night) for two days. Two-days-old seedlings were hydroponically grown in 0.2 mM CaCl2 solution (pH 4.3). For Al treatment, seedlings were exposed to 5 μM AlCl3. The solution was renewed every day. The relative root growth, the ratio of root elongation under Al treatment to control, was used as the indicator of Al tolerance. Root images were acquired by WinRHIZO and analyzed for total root length and relative total root growth according to Cai et al (2013). In addition, all three genotypes and another Al-sensitive cultivar Franklin (Hossain, Zhou, & Mendham, 2005) were grown on acid soil (pH, 4.3; exchangeable Al, 13.6 mEq/kg) collected to confirm their tolerance to acid soil in Launceston, Australia.