TOLERANCES OF WHEAT GERMPLASM TO ACID SUBSOIL

Aluminum toxicity is a major growth limiting factor for plants in many acid soils of the world. Correcting the problem by conventional liming is not always economically feasible, particularly in subsoils. Aluminum tolerant plants provide an alternative and long-term supplemental solution to the problem. The genetic approach requires the identification of Al tolerance sources that can be transferred to cultivars already having desirable traits. Thirty-five cultivars and experimental lines of wheat (Triticum aestivum L. em. TheII) were screened for Al tolerance on acid Tatum soil (clayey, mixed thermic, typic Hapludult) receiving either 0 or 3500 mg CaCO3/kg (pH 4.1 vs. pH 7.1). Entries showed a wide range of tolerance to the acid soil. On unlimed soil at pH 4.3, absolute shoot dry weights differed by 5-fold, absolute root dry weights by 6.5-fold, relative shoot weights (wt. at pH 4.3/wt. at pH 7.1 %) by 4.7-fold and relative root dry weights by 7-fold. Superior acid soil (Al) tolerance of 'BH-1146' from Brazil and extreme sensitivities of cultivars 'Redcoat' (Indiana, USA) and 'Sonora 63' (Mexico) were confirmed. Seven experimental (CNT) lines from Brazil showed a range of acid soil tolerance but were generally more tolerant than germplasm from Mexico and the USA. One line, 'CNT-1', was equal to BH-1146 in tolerance and may be useful in transferring Al tolerance to existing or new cultivars. Five durum cultivars (Triticum, durum, Desf.) were extremely sensitive to the acid Tatum subsoil at pH 4.3 compared with pH 7.1.