Sorghum seedling root growth as influenced by H+, CA++, and MN++concentrations1

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Abstract
Root response mechanisms for acid soil tolerance adaptability are generally unknown. Sorghum [Sorghum bicolor (L.) Moench] cultivars (Funk G522DR, GP140, SC599, TAM428, SC283, and SC574) were grown in white quartz flintshot sand and watered with 0.01M sodium acetate buffer at pH 4.0, 4.5, 5.0, 5.5, or 6.0 and Ca++ (0, 10, 100 mgl‐1 as CaCl2) or Mn++ (0, 1.4, or 140.0 mgl‐1 as HnCl2). At the acid soil tolerance impact response phase (< 10 days old), Ca++ did not influence initial root growth. Increased H+ concentration inhibited juvenile root growth equivalently in all six cultivars. This inhibition was reversed by exogenous GA3 in Funks G522DR but not in SC283 or SC574. Excess Mn++ (140 mgl‐1) further decreased root growth. Induction of an auxinase inhibitor by GA3 would support a hypothesis of H+ concentration influence on IAA transport and/or availability. Root growth matched IAA water partitioning and exogenous IAA (10‐10 and 10‐9 M) reversed the H+ concentration influence on root growth of SC283. We suggest that low pH (++, which is known to induce IAA oxidation, further exacerbates the deleterious growing conditions.