GA-responsive dwarfing gene Rht12 affects the developmental and agronomic traits in common bread wheat

Abstract

Opportunities exist for replacing reduced height (Rht) genes Rht-B1b and Rht-D1b with alternative dwarfing genes, such as the gibberellin-responsive gene Rht12, for bread wheat improvement. However, a comprehensive understanding of the effects and mode of action of Rht12 is lacking. In the present study, the effects of Rht12 were characterized by analyzing its effects on seeding vigour, seedling roots, leaf and stem morphology, spike development and carbohydrate assimilation and distribution. This was carried out in the four genotypes of F2:3 lines derived from a cross between Ningchun45 and Karcagi (12) in two experiments of autumn sowing and spring sowing. Rht12 significantly decreased stem length (43%∼48% for peduncle) and leaf length (25%∼30% for flag leaf) while the thickness of the internode walls and width of the leaves were increased. Though the final plant stature was shortened (40%) by Rht12, the seedling vigour, especially coleoptile length and root traits at the seedling stage, were not affected adversely. Rht12 elongated the duration of the spike development phase, improved the proportion of spike dry weight at anthesis and significantly increased floret fertility (14%) in the autumn sowing experiment. However, Rht12 delayed anthesis date by around 5 days and even the dominant Vrn-B1 allele could not compensate this negative effect. Additionally, grain size was reduced with the ability to support spike development after anthesis decreased in Rht12 lines. Finally, grain yield was similar between the dwarf and tall lines in the autumn sowing experiment. Thus, Rht12 could substantially reduce plant height without altering seeding vigour and significantly increase spikelet fertility in the favourable autumn sowing environment. The successful utilization of Rht12 in breeding programs will require careful selection since it might delay ear emergence. Nonetheless, the potential exists for wheat improvement by using Rht12.

Figure 1. Seminal root morphology of the dwarf and tall lines at the seedling stage determined by the Cigar method.

Panel A shows the dwarf lines and B shows the tall lines. The tall lines always have two more seminal roots than the dwarf lines (P<0.05).

Figure 2. Spike development of the tall (rrBB, A1–A3) and dwarf (RRBB, B1–B3) genotypes in the AS experiment.

A1 and B1 show spike development at the early double ridge stage of tall genotypes and at metaphase of single ridge stage of the dwarf genotypes at 630°Cd (75d after sowing), respectively; A2 and B2 show spike development at terminal spikelet initiation stage of the tall genotypes and at anaphase of double ridge stage of the dwarf genotypes at 770°Cd (165d after sowing), respectively; A3 and B3 show the floret morphology at yellow anther stage/anthesis of the tall genotypes and at green anther stage of the dwarf genotypes at 1430°Cd (209d after sowing), respectively. Scale bars = 100 µm.

Figure 3. Culm morphology of the four genotypes in the AS and SS experiments.

A: the mature plant morphology of the four genotypes and the two parents in the AS experiment. B: schematic representation of internode elongation patterns of the four genotypes and the two parents in AS experiment. C: Schematic representation of internode elongation patterns of the four genotypes in the SS experiment.

Figure 4. Development of plant height from the soil surface to the top ligule.

A: AS experiment, the final height is achieved at week 22. B: SS experiment, the final height is achieved at week 16. C: plants at the 7^th week in AS experiment, the yellow line shows the site of the top ligule in each genotype and the two parents.

Figure 5. Dynamic changes in dry weight of different organs in the main shoot after anthesis in the AS experiment.

A: dwarf lines; B: tall lines; C: spike dry weight of the dwarf and tall lines. The main culm comprises 6 internodes, the sixth internode is the peduncle. The leaves are numbered from the flag leaf down on the main stem. RR: dwarf lines; rr: tall lines.

Figure 6. Dynamic changes in dry weight of different organs in the main shoot in the SS experiment.

A: dwarf lines; B: tall lines; C: spike dry weight of the dwarf and tall lines. The main culm comprises 6 elongated internodes, the sixth internode is the peduncle. The leaves are numbered from the flag leaf down on the main stem. RR: dwarf alleles; rr: tall alleles.