Due to Taiwan's hot and humid climate, melon cultivation is vulnerable to various diseases such as powdery mildew, downy mildew, bacterial fruit blotch (BFB), and viruses. The impacts of extreme weather stresses, including low and high temperatures, further lead to increased control costs and reduced yield and quality. Traditional breeding often faces limitations such as lengthy breeding cycles and environmental interference when dealing with complex quantitative traits. This project aims to accelerate the breeding process of disease-resistant and resilient melon varieties through molecular marker technology and precise phenotypic evaluation.

In the first half of 2026, field self-pollination, purification, and germplasm propagation of melon S₂ lines (Nos. 1–20) were completed (Figure 1) to ensure a stable supply of materials for subsequent experiments. Meanwhile, genomic DNA extraction was performed on the aforementioned S₂ lines, and DNA quality and integrity were confirmed via A_260/A₂₈₀ ratio measurement and agarose gel electrophoresis, laying a solid foundation for subsequent molecular testing. In addition, a standardized artificial inoculation and disease evaluation protocol for bacterial fruit blotch (Acidovorax citrulli strain Aac25) was successfully established this period. Inoculation tests (Figure 2) were completed on the susceptible control 'Yinhui' and three S₂ selfed lines, clarifying the temporal changes of disease symptoms and the frequency of grading surveys, thereby effectively advancing the validation work of disease-resistant molecular markers and trait association analysis.

▲Figure 1. Fruit phenotypic diversity of melon S2generation germplasm.

▲Figure 2. Symptom expression on the 9th day after artificial inoculation with bacterial fruit blotch in melons. (A) Susceptible control cultivar 'Yinhui'; (B) Melon S₂ generation line No. 3; (C) Different levels of tolerance to Aac infection between cotyledons and true leaves on the same plant.