Reduced height alleles (Rht) and Hagberg falling number of wheat
Highlights
► GA-insensitive and GA-sensitive Rht alleles on falling number are contrasted. ► Instability in falling number often increases with dwarfism. ► There is discontinuity between Rht-B1c and Rht-D1c dwarfing and dormancy effects. ► There are genetic × system (organic v. conventional) effects on falling number.
Introduction
Hagberg falling number (HFN) is a quality criterion of bread-making wheat because of its negative association with α-amylase activity (Perten, 1964). Doughs formed from flour with excessive α-amylase are sticky and difficult to process, and when baked, produce discoloured loaves that are poorly structured (Chamberlain et al., 1982). Immoderate levels of α-amylase are most commonly produced in pre-harvest sprouting (PHS) or as late-maturity α-amylase (LMA) (Lunn et al., 2001). Pre-harvest sprouting follows a loss of grain dormancy and subsequent germination whilst in the ear, often in response to wet conditions occurring between grain ripeness and harvest (Barnard, 2001), and also as might occur in lodged crops. Late-maturity α-amylase occurs in the absence of visible sprouting (Mares and Mrva, 2008). Low HFN or high α-amylase activity in the absence of visible sprouting has been variously associated with: low temperatures and/or high soil moisture during the linear phase of grain filling (Gooding, 2010, Gooding et al., 2003); slow grain drying rate; abrupt temperature changes during grain filling; large grain size and mass; low specific weights, and grain cavity characteristics (Clarke et al., 2004, Evers et al., 1995, Farrell and Kettlewell, 2008, Farrell and Kettlewell, 2009, Kindred et al., 2005, Mares and Mrva, 2008). There are strong genotype × environment (Gooding, 2010), and genotype × agronomy (Kindred et al., 2005) interactions on HFN.
Reduced height (Rht) alleles (Gale and Youssefian, 1985) are incorporated in wheat breeding programmes to produce semi-dwarf wheats (Flintham et al., 1997a). The gibberellin (GA)-insensitive alleles Rht-B1b and Rht-D1b (from Norin 10, syn. Rht1 and Rht2), and the GA-sensitive allele Rht8c (from Akakomugi, often linked with the photoperiod-insensitivity allele Ppd-D1a) individually: reduce height by 10–15%; reduce lodging in fertile and humid conditions; and increase harvest index when added to excessively tall backgrounds (Flintham et al., 1997a, Gooding et al., 2012). Rht alleles that confer reduced GA sensitivity have reduced grain α-amylase activity and increased HFN (Flintham et al., 1997b, Gooding et al., 1999). Gibberellin activity and sensitivity is implicated in PHS and in the production of LMA (Flintham et al., 1997b, Mares and Mrva, 2008). The benefit of GA-insensitivity for HFN has been particularly evident for the severe-dwarfing allele Rht-Blc (from Tom thumb, syn. Rht3) with reduced risk of PHS (Flintham et al., 1997b). Rht-B1c, unlike the Norin 10 semi-dwarfing alleles, confers marked inhibition of aleurone activity when challenged with GA (Flintham and Gale, 1982), possibly contributing to increased grain dormancy. A severe-dwarfing allele is also present at the Rht-D1 locus (Rht-D1c, syn. Rht10, from Ai-Bian), but we are unaware of the previous work characterizing the effects of this allele on grain dormancy and HFN. Both Rht-B1c and Rht-D1c in the homozygous state produce plants with statures sub-optimal for yield (Addisu et al., 2010), but it has been suggested that Rht-B1c may have utility in the heterozygous state, or by controlling height in particularly tall backgrounds, or even triticale (Flintham et al., 1997b).
The benefit of GA-insensitivity for HFN has raised concerns as to the effects of replacing the Norin 10 alleles with Rht8c in breeding programmes (Mares and Mrva, 2008). Here we use near-isogenic lines (NILs) to compare the effects of semi-, and severe-dwarfing alleles at the Rht-B1 and Rht-D1 loci with GA-sensitive alleles conferring both semi- (Rht8c+Ppd-D1a linkage block on chromosome 2D) and severe- (Rht12, gamma ray-induced allele from ‘Karcagi 522’) dwarfing. We also compare 62 doubled-haploid (DH) progeny of cv. Savannah (Rht-D1b) × Renesansa (Rht8c+Ppd-D1a) genotyped with markers for the dwarfing genes and Ppd-D1a to assess the effects of the alleles individually and in combination. Allele effects on HFN are assessed for stability over contrasting genetic backgrounds, seasons and systems (‘intensive’ v. ‘organic’) and interpreted with reference to mean grain weight, grain specific weight, α-amylase activity, and the acquisition and retention of grain dormancy.
Section snippets
Crop husbandry
All experiments were conducted within the same 10 ha site at the Crops Research Unit, Sonning, University of Reading, UK (51°29′N, 0°56′W), on a free-draining sandy loam. The site is split between an area receiving synthetic agrochemicals and fertilizers, managed intensively, and an area managed organically since 2001. Full details of the site, crop establishment and husbandry are available elsewhere (Addisu et al., 2009, Addisu et al., 2010, Gooding et al., 2012). Untreated seeds were drilled
Near-isogenic lines
Averaged over Background, the semi-dwarfing alleles, Rht-B1b and Rht-D1b, reduced height significantly by about 15% (Table 2). The severe-dwarfing allele Rht-B1c reduced height by 48%. In the Mercia background, the Rht-D1c NIL was shorter than Rht-B1c. The GA-sensitive combination of Rht8c+Ppd-D1a produced heights comparable to the GA-insensitive semi-dwarfing alleles. Rht12 produced the shortest plants despite being GA-sensitive. In the taller backgrounds (M. Huntsman and M. Widgeon) the
Discussion
We confirm the association between GA-insensitivity conferred by dwarfing alleles and a positive effect on the HFN (and/or a negative effect on α-amylase) of wheat (Flintham et al., 1997b, Mares and Mrva, 2008, Tan et al., 2010). We report the mean effect of Rht-D1c to be consistent with this association. However, we also demonstrate this benefit of GA-insensitivity to be unstable over season, growing system and genetic background. Despite the similar mean effects of Rht-B1c and Rht-D1c, there
Conclusions
GA-insensitive dwarfing alleles, including Rht-D1c, can help maintain HFN in wheat but this effect depends on background, season and system. Increased grain dormancy during and after crop maturation is not a universal consequence of reduced GA-insensitivity even when dwarfing, as with Rht-D1c, is severe: rather, it appears associated only with Rht-B1c. The Rht8c+Ppd-D1a linkage block is associated with reduced HFN, although the association appears closer to Ppd-D1a than with Rht8c. The negative
Acknowledgements
The authors are grateful to the Felix Trust and Eastern University, Sri Lanka for providing scholarships for M. Addisu and K.D. Harris, respectively, and to R.J. Casebow, C.J. Hadley, R.E. Kiff and D.T. Smith for technical support. C. Uauy acknowledges support from the UK Biotechnology and Biological Sciences Research Council (BBSRC) (BB/H018824/1).
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2021, Molecular PlantCitation Excerpt :More specifically, Rht-B1b and Rht-D1b reduce stem elongation but do not affect α-amylase production in the grain during germination (Gale and Marshall, 1973; Wu et al., 2011). This is in contrast with the phenotype of Rht-B1c, which has reduced GA sensitivity for both stem elongation and α-amylase production (Gale and Marshall, 1973; Wu et al., 2011), and is therefore more dormant than wild-type (Gooding et al., 2012; Derkx et al., 2017). Rht-D1c, also being severely dwarfed, does not exhibit the strong dormancy observed in Rht-B1c (Gooding et al., 2012).
Global Journeys of Adaptive Wheat Genes
2019, Applications of Genetic and Genomic Research in CerealsPreharvest sprouting and α-amylase activity in soft winter wheat
2018, Journal of Cereal ScienceCitation Excerpt :Either method should serve as a reliable phenotyping method to identify and characterize sprouting resistance. The relationship between HFN and αAmy has been demonstrated in multiple studies (Gooding et al., 2012; Hagberg, 1961; Moot and Every, 1990). Phenotyping misted-αAmy will provide estimates of HFN under sprouting conditions, allowing breeders to select for this important trait for grain quality, even during growing seasons where sprout inducing field conditions are absent.
Gibberellin-sensitive Rht alleles confer tolerance to heat and drought stresses in wheat at booting stage
2016, Journal of Cereal ScienceCitation Excerpt :Under the rising momentous of Rht dwarfing alleles in world’s wheat production, their significance may rise with changing climatic scenario. Despite acknowledged benefits of Rht alleles, it has been claimed that these alleles may have detrimental effects on grain quality under challenging conditions of heat and drought stress (Law and Worland, 1985; Gooding et al., 2012). Therefore, clear understanding regarding the GA-insensitivity of Rht alleles on the tolerance to high temperature and drought stress at booting stage and their impact on grain yield and quality is inevitable.