Analysis of interaction between minor-effect restoring gene and sowing date reveals the fertility sensitivity to CMS lines in <italic>indica</italic> rice

<p indent="0mm">In 1960, Longping Yuan serendipitously discovered a natural hybrid rice variety with distinct advantages over others in an experimental field. After extensive research and exploration, he suggested the ‘three-line method’ breeding approach to harness rice heterosis by incorporating male-sterile, maintainer, and restorer lines. He also emphasized that using rice male sterility was the most effective way to solve the problem of large-scale seed production through the exploitation of rice heterosis in 1966. The yield per unit area of hybrid rice increased by approximately 20% compared to conventional dwarf varieties, marking a significant breakthrough in rice production. Post-tobacco seed production refers to the hybrid rice seed production in farmland after the tobacco harvest. This represents a new farming system model aimed at adjusting the industrial structure of the southern seed production region. Cytoplasmic male sterility (CMS) lines are the cornerstone of the three-line hybrid rice system. Moreover, the varying degrees of sterility in CMS lines directly impact the seed purity of hybrid rice. This experiment was carried out during the post-tobacco seed production period to explore the genetic basis of dark pollen using I₂-IK dyeing and florets with fertile anthers, which were caused by the interaction between restoring genes with a minor-effect restoring genes and other factors. The study was conducted using four sowing dates and two experimental locations to observe changes in male fertility among five CMS lines (Zhenshan 97A, Longtepu A, Yiexiang A, Jinfu 1A, and 301A), which contain different numbers of restoring genes. The rates of dark pollen dyed by I₂-IK and florets with fertile anthers were analyzed using the additive main effects and multiplicative interaction model (AMMI). The results indicate that the recovery of CMS fertility is not only impacted by major genes but also by the cumulative effects of minor genes. Longtepu A should be categorized as a type with a relatively large number of minor effect-restoring genes, making it more sensitive to changes in sowing dates and experimental locations. Yexiang A, Jingfu 1A, and 301A were categorized as intermediate types of minor-effect restoring genes, demonstrating some degree of response to factors such as sowing dates. Zhenshan 97A was identified as a type with a relatively small number of minor-effect restoring genes and low sensitivity to sowing time. The sensitivity of CMS lines to sowing dates, ranked from highest to lowest, is as follows: Longtepu A, 301A, Jingfu 1A, Yexiang A, and Zhenshan 97A. In order to ensure seed purity during post-tobacco seed production and reproduction, it is recommended to advance the sowing date appropriately based on the impact of sowing dates on the sterility of CMS lines. Furthermore, genetic breeding and purification of CMS lines should be conducted at sowing dates when the minor-effect restoring gene is highly expressed. This approach will facilitate the early elimination of unqualified individual plants or lines and accelerate the development of a stable population with infertility.