Abstract:

【Objective】 The aim of this study is to use molecular marker to construct a breeding system to improve the traditional breeding method,thereby reducing breeding costs and improving breeding efficiency. At the same time, it lays a theoretical foundation for the formation of a new breeding system. 【Method】 The F₂ population was constructed by crossing the photosensitive(non-heading) forage sorghum variety Jinguang 1R as female and the photo insensitive(heading) sorghum variety BMRC-3-2 as male. According to heading and non-heading phenotypes, F₂ population was divided into two groups. Thirty plants were selected from each group and DNA was extracted from leaves, SSR and BSA were used to map photosensitive genes in F₂ population of Jinguang 1R/BMRC-3-2 and screen for specific SSR primers. The specific primers were used to identify the photosensitivity trait in F₁ generation（F₁ Hybrids breeded from high generation stable restorer line with Jinguang 1R as parent and matched with other male sterile lines）, and the final target primers were determined by comparing with the phenotype in the field, so as to construct a new photosensitive breeding system for forage sorghum. 【Result】 After SNP index analysis, the region of about 250 Kb before and after the highest point of 99% threshold line was selected as the candidate region for trait correlation. The total length of the region was 500 kb, with 400 SNP loci, and six of them were non-synonymous mutations or stop gain or stop loss SNP loci. Finally, two candidate genes were identified to be related to photosensitivity, which were located on chromosome 7. A pair of specific primers 70.2-3 was developed by SSR. The primers can distinguish between heading and non-heading sorghum plants to a great extent. The results showed that according to the "single peak" at 251bp, the accuracy of primers 70.2-3 in the identification and selection of 50 non-photosensitive F₁ hybrids reached 100%, and all the materials showed a peak value near 251bp. Based on the "double peaks" in the vicinity of 214 bp and 251 bp, the accuracy rate of the primer for the identification and selection of the other 50 photosensitive F₁ hybrid species reached 90%. Three materials, No. F₁-69, F₁-70 and F₁-71, showed "double peaks" near 214 bp and 262 bp. Material F₁-81 has a "single peak" at 251bp, while material No. 86 has a "double peak" near 251 bp and 232 bp.【Conclusion】 In this study, we revealed that the candidate genes controlling heading date of sorghum were LOC8068537 and LOC8068548, which were between 810000 and 1310000 bp on chromosome 7 of sorghum. The acquisition of specific primers 70.2-3 improved the traditional breeding methods. The primer validation in laboratory could replace the field crossing observation, saving the breeding cost and improving the breeding efficiency.

Key words: forage sorghum, photosensitive type, molecular markers