Evaluation on Chinese Bread Wheat Landraces for Low pH and Aluminum Tolerance Using Hydroponic Screening

Aluminum (Al) toxicity often takes place in acidic soils with a pH of 5.5 or lower. Breeding and cultivation of Al tolerance wheat can partially protect wheat escaping from Al toxicity. The scarcity of the tolerant sources impedes the wheat breeding. In order to find new Al tolerance sources, we screened 173 bread wheat landraces from Tibet of China using hydroponic screening. It was indicated that: (1) There were diversities on the root regenerate length (RRL). The RRL of a large of landraces were longer than 7.00 cm in pH 7 (58.38%) and pH 4.5 (66.47%), but shorter than 5.00 cm in pH 4.5 + 50 μM Al3+(80.93%). The low pH showed either promotion or restraining effects depend on landraces, but Al toxicity under low pH only showed restraining effects on the root elongation. (2) There were also diversities on root tolerance index of low pH (RTI1) or root aluminum tolerance index (RTI2) among cultivars. The RTI1 varied from a narrow range but with relatively high value (0.8722-1.2953) in comparison with that of RTI2 (0.3829-1.0058), and the RTI1 of approximately 60% landraces was higher than 1.0000, the RTI2 of only 19.07% landraces was higher than 0.7000, suggesting that Al toxicity acted as an important factor for the reduction of the root elongation under acidic soils. (3) The RTI1 of many wheats was higher than 1.0000, and As2256 and As2295 were the most tolerant for low pH, with RTI1 1.2953 and 1.2925, respectively. (4) Based on RTI2, seven wheats showed similar or higher tolerance to Al toxicity than Chinese Spring (CS), a known tolerance wheat. Much better tolerance existed in landraces of As1543 and As1242, which can be used as the new parents for Al tolerant breeding.