Agronomic Trait and Gene Analysis of Diangu 1839, a Newly Bred Fragrant and Soft Rice Variety Derived from Diantun 502 in Yunnan, China

The fragrant and soft rice variety Diantun 502 has been a major cultivar for high-quality rice production in Yunnan Province since its approval in 1993. Over 30 years of widespread cultivation, several issues affecting this variety—including high susceptibility to rice blast, reduced yield, and declining quality—have been noted. To address these limitations, this study aimed to improve and upgrade Diantun 502. During the breeding process, parent lines with soft rice traits were selected, and molecular marker-assisted selection was employed using the soft rice gene Wxhp and the fragrance gene badh2. Priority was given to grain quality while also considering agronomic performance. Natural induction tests were conducted in rice blast-prone regions. After 9 years of selection and evaluation, the new variety—Diangu 1839—was successfully developed. Comparative analysis of agronomic and economic traits, as well as gene loci between Diantun 502 and the improved variety Diangu 1839, revealed that the observed trait changes in Diangu 1839 corresponded with the presence of the targeted gene loci. This study involved a comparative analysis of agronomic and economic traits as well as key gene loci between Diantun 502 and the improved variety Diangu 1839. The results showed that, compared to Diantun 502, Diangu 1839 achieved a 14.1% increase in yield and a significant 25.6% reduction in chalky grain rate. Importantly, the retention of badh2 and Wxhp genes ensured the preservation of excellent eating quality, while rice blast resistance was enhanced. Although Diangu 1839 demonstrated significant improvements in yield, rice quality, and disease resistance, its resistance to brown planthopper remains limited due to the lack of corresponding resistance genes. The technical system and breeding experience established in this study provide important technical references for the genetic improvement of high-quality, fragrant, and soft rice varieties.