ALUMINUM TOLERANCE OF 1BL.1RS AND 1AL.1RS NEAR-ISOLINES IN SOFT RED WINTER-WHEAT

Some cultivars containing the 1BL.1RS wheat (Triticum aestivum L.)-rye (Secale cereale L.) translocation are presumed tolerant to aluminum ( Al) toxicity, but whether this tolerance is due to genes on 1RS or to genes in the wheat genome is not clear. A set of backcross-six, F-2-de rived F-4 near-isolines containing either the 'Kavkaz'-derived 1BL.1RS or 'Amigo'-derived 1AL.1RS translocation were developed in five soft red winter wheat backgrounds at Columbia, MO between 1988 and 1992. Th e presumed contribution of 1RS to Al tolerance expressed in solution c ulture was measured using a split-plot design, replicated four times. Seedlings were grown for 4 d in an aerated, low-ionic-strength, hydrop onic solution at pH 4.0 containing no phosphorus. Whole-plot treatment s included 1 mg L(-1) Al as AlCl3 and a zero Al control. The longest s eminal root of each seedling was measured and averaged across seven se edlings per isoline. Root tolerance index (RTT), calculated as the mea n seminal root length in the Al treatment divided by the mean seminal root length in the control, provided a measure of Al tolerance. Higher RTI values indicated greater Al tolerance. Mean RTI values for each b ackground, averaged across 1AL.1RS and 1BL.1RS isolines, ranged from 0 .63 in 'MO 11728' to 0.24 in 'Caldwell'. 1AL.1RS significantly reduced Al tolerance in 'Becker', Caldwell and 'MO 10501', but had no effect on Al tolerance in MO 11728 and 'Pioneer 2551'. 1BL.1RS had no effect on Al tolerance in any genetic background. Neither the Kavkaz- nor the Amigo-derived IRS segment contained genes for Al tolerance when grown in solution culture, and improved Al tolerance previously reported in 1BL.1RS cultivars was due to coincidental major genes on the wheat ge nome.