The GRF9-6Ab Allele Compensates for the Pleiotropic Deficits of the Ddw1 Dwarfing Gene in Triticale

The Ddw1 dwarfing gene is pivotal for reducing plant height and improving lodging resistance in triticale, but its pleiotropic effects on yield components and heading date pose significant challenges for breeders. This study identifies the Growth-Regulating Factor 9-6A (GRF9-6A) gene that compensates for these drawbacks. Field trials across locations (Moscow, Krasnodar) and years (2018, 2019) confirmed the effect of Ddw1, reducing plant height by 26.1–30.1 cm (31.8–32.5%) and thousand-kernel weight (TKW) by 6.0–6.3 g (11.8–15.7%) while increasing the harvest index by up to 4.8 percentage points in three out of four environments, with its effect nullified under the heat stress of Krasnodar 2019. In a Ddw1 background, the GRF9-6Ab allele distinguished by a 12 bp deletion in its promoter compensated for yield losses by increasing grain weight per main spike by up to 0.34 g (19.2%) via boosts in grain number per spike (up to 11.6%) and TKW (up to 11.5%). This combination also elevated the harvest index by up to 4.0 pp and, critically, provided a key agronomic advantage by accelerating heading by 6.3–6.5 days (10.0–10.2%), thereby mitigating the Ddw1-associated developmental delay. Our results demonstrate that pyramiding Ddw1 with the GRF9-6Ab allele the development of semi-dwarf, high-yielding, and early-maturing triticale cultivars for food and forage. This breeding strategy, facilitated by a newly developed diagnostic marker for GRF9-6Ab, is particularly advantageous for cultivation in environments similar to the Central Non-Chernozem region.