SCREENING WHEAT AND OTHER SMALL GRAINS FOR ACID SOIL TOLERANCE

Aluminum (Al) toxicity in acid soils is a major growth-limiting factor for cereal crops in many parts of the world. The most striking effect of high Al concentration in acid soils is stunting of the root system . Liming reduces Al toxicity in surface soils; however, cereal breeder s must be prepared to develop cultivars that have tolerance to soil ac idity. A 4 day root bioassay, originally used to identify Al toxic soi ls, was adapted to evaluate tolerance to soil acidity of cereal specie s and genotypes. Acid soil tolerance was related to the extent of inhi bition of root elongation in an Al-toxic soil (pH 4.2) relative to roo t elongation in the same soil treated with lime (pH 5.2). Of the entri es, 18% were tolerant or moderately tolerant, and 48% were susceptible or moderately susceptible when 75 bread wheat (Triticum aestivum L.) genotypes were tested. None of the 22 entries of durum wheat (Triticum durum Desf.) were tolerant or moderately tolerant, indicating much lo wer adaptability to soil acidity than bread wheat. The following ranki ng of acid soil tolerance of cereal species was obtained: rye (Secale cereale L.) > oats (Avena sativa L.) > millet (Panicum miliaceum L.) > bread wheat (Triticum aestivum L.) > barley (Hordeum vulgare L.) > du rum wheat (Triticum durum Desf.). Variation in tolerance within the ot her cereal species was much lower than within bread wheat species. The root bioassay method is relatively quick, simple and inexpensive. The method can also be used to screen early-generation populations becaus e assayed seedlings are still viable and can be transplanted for growi ng until harvest.