The three-way interaction of varietal emergence capabilities, rht semi-dwarfing alleles, and GA3 seed application from deep planted wheat (Triticum aestivum L)

Authors: HORGAN, ANDREW - Washington State University; Garland-Campbell, Kimberly; CARTER, ARRON - Washington State University; Steber, Camille

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2021
Publication Date: 2/19/2021
Citation: Horgan, A.M., Garland Campbell, K.A., Carter, A.H., Steber, C.M. 2021. The three-way interaction of varietal emergence capabilities, rht semi-dwarfing alleles, and GA3 seed application from deep planted wheat (Triticum aestivum L). Agrosystems, Geosciences & Environment. 4(1). Article e20144. https://doi.org/10.1002/agg2.20144.
DOI: https://doi.org/10.1002/agg2.20144

Interpretive Summary: In dry or semi-arid environments, wheat grain is planted deeply to reach the moist soil needed for seed germination. It is very important that wheat seedlings elongate well in such environments so that they reach sunlight before they run out of stored seed nutrients. Dwarfing genes are widely used to improve wheat yield by preventing lodging, or falling over, when plants become too tall. These include alleles causing GA hormone-rescued dwarfism in Rht8 and GA-insensitive dwarfism in Rht-B1b and Rht-D1b. GA hormone seed treatments are used to rescue seedling elongation, but can also result in excessive elongation of the subcrown internode which in turn can desiccate seedlings by taking some of their roots out of the soil. We examined the effects of GA treatment on different seedling tissues, including the sub-crown internode, coleoptile, and first leaf, in normal height plants, and in plants carrying the Rht8, Rht-B1b and Rht-D1b dwarfing genes. GA insensitivity was associated with lack of GA response in seedling tissues, while GA-sensitivity in normal and Rht8 varieties was associated with coleoptile or subcrown internode elongation in response to GA hormone seed treatment. Interestingly, some better emerging GA-insensitive wheat varieties had longer coleoptiles and/or subcrown internodes, suggesting that increased seedling elongation has resulted from selection for better emerge in semi-arid regions of the U.S. northwest.

Technical Abstract: One of the chief determinants of wheat yield in semi-arid environments is the ability to germinate and emerge after deep sowing into stored soil moisture. The widely used reduced height (Rht) alleles for semi-dwarf stature are insensitive to the plant hormone gibberellin A (GA). In the presence of these alleles plant stature and coleoptile length is significantly decreased, reducing the emergence percentage of these semi-dwarf cultivars. The seed industry counteracts these effects with GA seed treatments to promote better emergence. Unfortunately, excessive sub-crown internode elongation may also occur after GA seed treatment. Our objectives were to investigate the response of different seedling tissues, including the sub-crown internode, coleoptile, and first leaf, to GA seed treatment in a collection of genotypes differing for Rht dwarfing alleles and ability to emerge from deep planting. Comparison of near-isogenic lines carrying either no dwarfing allele or the GA-insensitive Rht-B1b or Rht-D1b semi-dwarfing alleles showed that GA insensitivity was associated with lack of GA response in seedling tissues. Consistent with this, GA sensitive cultivars carrying either no dwarfing gene or the Rht8 dwarfing gene responded to GA through elongation of the coleoptile and subcrown internode. Interestingly, some better emerging GA-insensitive cultivars had longer coleoptiles and/or subcrown internodes, suggesting that increased seedling elongation has resulted from selection for better emerge in semi-arid regions of the U.S. northwest.