TOLERANCE OF SOYBEAN GERMPLASM TO AN ACID TATUM SUBSOIL

Aluminum tolerant soybean cultivars are needed for deeper rooting and increased drought tolerance in acid subsoils. Fifteen cultivars or plant introductions were screened for Al tolerance by growing them for 33 days in pots of unlimed (pH 4.3) and limed (pH 5.6) Tatum subsoil. Tolerance was based upon plant symptoms on unlimed soil (leaf cupping, chlorosis or necrosis, and petiole collapse), absolute dry-weights of shoots and roots on unlimed soil and relative (unlimed/limed %) shoot and root weights. On unlimed soil, absolute dry weights ranged 4-fold for shoots and 7-fold for roots. Relative weights (unlimed/limed %) ranged 2.7-fold for shoots and 6-fold for roots. Based on these criteria, entries P1248511 (Japan), Perry (USA), P1381674 (Uganda), Amcor (Ohio USA) and Hernon 147 (Zimbabwe, Africa) were judged most tolerant to the acid soil. Most sensitive entries included Sable, Oribi and Duiker, all from Zimbabwe, Africa, and Chief (USA). Santa Rosa (Brazil) was only moderately tolerant. Entries from Zimbabwe, Africa showed a range of acid soil tolerance. Hernon 147 was most tolerant, Oribi and Sable least tolerant and Buffalo and Impala intermediate. None of the introduced gerrnplasm was superior to Perry in acid soil tolerance. Amcor (Ohio, USA), reportedly tolerant to low soil fertility and drought, was more tolerant to acid Tatum soil than Beeson (Indiana USA). Results suggest that Amcor soybean, like some Ohio cultivars of wheat and barley, may have been exposed to Al during its breeding history. Entries producing highest shoot and root dry weights on unlimed soil were also generally more vigorous on limed soil. Thus, overall vigor may contribute to Al tolerance. Similar observations have been made for selections of Ky 31 tall fescue. Our results suggested that shoot growth alone was an adequate index of acid soil tolerance among the soybean entries tested. Mineral element concentrations in plant shoots were not useful in understanding differential acid soil tolerance.