Breaking Transgressive Photoperiod Sensitivity Barrier Triggered by Breeding Introgression of Pigm in Early-Mature Geng/Japonica Rice

Abstract

Heilongjiang and Jilin's early-maturing Geng / japonica (EMG) rice—grown at the world's northernmost latitude—delivers 17.3% of China's rice grain from only 16.0% of the national paddy area, yet every newly approved cultivar must combine early heading (EH) and blast resistance (BR). Transgressive photoperiod sensitivity (TPS), a unique form of photoperiod sensitivity, describes the phenomenon of pronounced heading delay in progenies relative to parents. Northward adaptation has driven major photoperiod regulators—including Hd1 , Ghd7 , and others—toward predominantly non-functional haplotypes in Heilongjiang EMG cultivars such as Kongyu 131 (KY131). However, TPS still occurs when using KY131- Pigm as a donor, hindering the introgression of elite genes such as Pigm for BR improvement in EMG rice. Despite the advances in regulators of photoperiod sensitivity, the specific gene(s) responsible for TPS in EMG backgrounds and the optimal editing target(s) to overcome this bottleneck remain largely unclear. Here, we integrate forward and reverse genetics to genetically dissect TPS generated during Pigm introgression into EMG backgrounds. Two major loci, qHD6 and qHD7 , harboring known candidate genes were identified. We further propose an updated biotech breeding strategy with two options for stacking BR in EMG rice while minimizing TPS by targeting these two loci.