Genome-Wide Analysis and Breeding Value of Yun1032S, a Novel Japonica P/TGMS Line Bred in the Low-Latitude Plateau

Two-line hybrid rice breeding relies on photoperiod-/thermosensitive genic male sterile (P/TGMS) lines with reliable fertility transition across different environments. The fertility of japonica P/TGMS lines is intricately regulated by photoperiod and temperature, making it more challenging to breed japonica sterile lines with stable sterility than indica sterile lines. This complexity is one of the primary reasons the breeding and promotion of two-line japonica hybrid rice has lagged behind that of indica hybrid rice. Here, we report on Yun1032S, a novel japonica P/TGMS line bred in the low-latitude plateau. It was bred by crossing Peiai 64S, the famous P/TGMS line with the largest application area in China, with Yungengyou 1, a plateau japonica variety noted for its excellent cold tolerance and disease resistance. Yun1032S exhibited stable sterility and female-parent traits favorable for two-line seed production. The elite combination YLY7706 (Yunliangyou7706), derived from a cross between Yun1032S and Yungenghui7501, showed a stable and competitive yield and strong disease resistance in the 2022–2023 Yunnan provincial regional trials. To analyze the genetic basis of phenotypes, we performed whole-genome resequencing and functional loci analysis of the parents and found that they carry a great number of superior alleles, which account for their yield and disease-resistant performance. To assess the breeding value of Yun1032S, we analyzed heterosis of a new batch of combinations derived from Yun1032S and identified a new combination, Jian3, with greater yield potential than YLY7706. These findings not only enhance the breeding of japonica P/TGMS lines but also provide direction for future pairing of two-line hybrid combination breeding. The study presents innovative concepts that further integrate genomics with traditional breeding techniques. Ultimately, Yun1032S marks a significant milestone in japonica P/TGMS line breeding technology, opening new avenues for the development of the two-line system.