Seedling elongation responses to gibberellin seed treatments in wheat

Abstract

The wheat (Triticum aestivum L.) Reduced height (Rht) alleles are widely used to prevent lodging through semi-dwarfism. Seedling elongation and coleoptile length can be significantly decreased by some of these alleles, leading to reduced soil emergence after deep sowing in certain semi-arid environments. Application of the elongation-promoting hormone gibberellin A3 (GA3) as a seed treatment has been used as an alternative to improve seedling emergence. Seedling responses to GA3 seed treatment were investigated under controlled conditions in a collection of varieties differing for Rht dwarfing alleles and the ability to emerge from deep planting. Data between treated and untreated seed were collected on overall coleoptile length and emergence from deep planting in simulated pot studies. Gibberellin-sensitive varieties, carrying either no dwarfing gene or the Rht8 dwarfing gene, responded to the GA3 seed treatment with increased coleoptile and subcrown internode elongation. Comparison of near-isogenic lines carrying no dwarfing allele or the GA-insensitive Rht-B1b and/or Rht-D1b semi-dwarfing alleles showed that GA insensitivity was associated with reduced seedling response to GA3 seed treatment. However, there was variation in seedling elongation and GA3 response in a collection of GA-insensitive varieties. Thus, it cannot be assumed that all Rht-B1b and Rht-D1b varieties will fail to respond to GA3 seed treatment. Interestingly, some better emerging GA-insensitive varieties had longer coleoptiles after treatment, suggesting that selection for better emergence in semi-arid regions of the U.S. Pacific Northwest may have led to responses in GA3 application independent of the dwarfing gene used.