Optimizing wheat grain yield: effects of Rht (gibberellin-insensitive) dwarfing genes

Abstract

Four sets of near-isogenic lines carrying different combinations of the alleles Rht-B1b, Rht-D1b and Rht-B1c for gibberellin-insensitive dwarfism in hexaploid wheat (Triticum aestivum L.) were compared with tall controls in a series of yield trials in eastern England and central Germany. In all four varietal backgrounds the effects of Rht-B1b and Rht-D1b were similar (plant height ≈ 86 and 83% of tall controls respectively) and in combination reduced plant height to c. 58%. The Rht-B1c allele caused more severe dwarfism (c. 50%) and, when combined with Rht-D1b, reduced plant height still further to c. 41%.Data from the trials were consistent with a model for height/yield relationships in which the pleiotropic effects of the Rht alleles on yield can be inferred from their primary function: insensitivity to gibberellin limits stem extension growth, decreasing assimilate demand for this organ and diverting it to the developing ear (which is not itself dwarfed). The net balance between the resulting increase in harvest index and the curvilinear relationship observed between plant height and total shoot yield results in optimum grain yields at intermediate plant heights.Yield advantages of shorter plants over tall controls were evident over several trials with mean grain yields ranging from 200 to 760 g m−2. The optimum plant height for yield improvement in different genetic backgrounds was achieved by different Rht alleles according to the background varietal height, such that intrinsically taller genotypes required more potent Rht alleles to achieve maximum potential grain yield.Ear yield components showed increases in grain number due to Rht pleiotropy, from which it is inferred that the number of grains per ear is limited by supply of assimilates pre-anthesis. Increases in grain number were associated with decreases in mean weight per grain which varied according to severity of dwarfism and varietal background, so that the net effect on grain yield per ear was sometimes positive, sometimes negative, and sometimes neutral in different Rht/variety combinations.

Genome-wide association analysis for lodging tolerance and plant height in a diverse European hexaploid oat collection

“…During the Green Revolution, reduction of plant height was one of the main breeding targets for cereals, leading to an increase in grain yield. However, this process seems to have some physiological limitations, and further reduction of plant height may negatively affect yield potential (Flintham et al 1997;. Therefore, QTL that affect lodging without affecting height can be of great value in further reducing lodging resistance.…”

“…A few dwarfing genes are available in oat that have been successfully used in the last decades by breeders, producing high-yielding varieties with lower lodging risk (Marshall and Murphy 1980;Milach et al 1997;Morikawa et al 2007). However, reducing plant height too much can have a detrimental effect on yield potential (Flintham et al 1997). Knowledge about genetic factors controlling stem strength and root anchorage in cereals and their effect on lodging tolerance is scarce, probably because these are complex traits that may be affected by many factors (e.g.…”

Putting genes into genetic coefficients

“…Because the dwarf and non-dwarf near-isogenic lines are virtually identical for all other genes, the differences between the two lines in the same environment can be attributed to their dwarfing gene differences. For example, Flintham et al (1997) grew semidwarf and dwarf near-isogenic lines of 'Maris Huntsman', 'Maris Widgeon', 'Bersee', and 'April Bearded' wheat in six trials to study the effect of the dwarfing genes. The lines grew to different heights in each environment (e.g., April Bearded, a tall or conventional height cultivar, was 1.30, 1.54, 1.27, 1.50, 1.39 and 1.48 m in Trials 1-6, respectively).…”

“…A full dwarf line has both Rht-B1b and Rht-D1b in the homozygous condition (e.g., Rht-B1b Rht-B1b and Rht-D1b Rht-D1b). A full dwarf is shorter than either semidwarf but is also shorter than if the effects (in this case the proportional plant height) of the two semidwarf genes were multiplicative (Flintham et al, 1997; Table 1). Hence, the presence of one semidwarfing gene increases the effect of a second semidwarfing gene.…”

Screening of Wheat (Triticum aestivum L.) Genotypes for Lodging Tolerance Using Morpho-Physiological Traits

“…Similar results were reported by Min (2001). Flintham et al, (1997) observed that in wheat plant height between 70 cm and 100 cm was best for maximum photosynthetic capacity in a canopy. Though, the plant height was positively correlated with total dry weight, it was negatively correlated with stem strength, chain weight, LRFI, grain yield and harvest index.…”