Utilizing multi-trait selection indices for genetic characterization and SSR marker validation linked to powdery mildew resistance in sunflower

In india sunflower, an important crucial oilseed crop, has endured considerable yield declines over the past two decades. One of the factor in the vulnerability of the reduced cultivation to powdery mildew disease. This persistent challenge underscores the pressing necessity for resistant germplasm and robust molecular markers to advance breeding initiatives. In this study, the phenotypic diversity of 20 sunflower inbreds was assessed for traits during two seasons (winter 2022, rainy season 2023). Using three multi trait selection indices Genotype-by-Yield-Trait (GYT) biplot, the Multi-Trait Genotype-Ideotype Distance Index (MGIDI) and the Factor Analysis and Interaction Best Linear Unbiased Prediction (FAI-BLUP) were used to evaluate the inbred lines. The inbreds were screened for powdery mildew resistance under both natural (winter 2022, rainy season 2023) and artificial conditions (summer 2023). Significant variation was observed for all traits, with four inbreds (COSF 6B, COSF 10B, COSF 12B and COSF 15B) exhibiting high oil content, seed yield and oil yield per plant. The inbreds COSF 6B, CSFI-17008 and CSFI-17024 consistently achieved the highest rankings across all indices, demonstrating strong potential for exploitation breeding programmes. SSR marker-based cluster analysis using DARwin software grouped the inbreds into five distinct clusters and STRUCTURE analysis revealed five sub-populations. Out of 141 SSR markers tested, 92 primers were polymorphic, with ORS898, ORS188, ORS1008 and ORS725 identified as the most effective. Marker validation using ORS 684 and ORS1110, both linked to powdery mildew resistance, showed that ORS 684 explained 27.17% of phenotypic variation and reliably distinguished resistant and susceptible inbreds. Notably, CSFI 17018 and CSFI 17020 exhibited resistance under both screening conditions and their resistance was further confirmed by marker validation. Based on diversity analyses and artificial screening, we recommend utilizing the identified diverse inbreds-COSF 6B, COSF 10B, COSF 12B, COSF 15B, CSFI 13023, CSFI 17008, CSFI 17018 and CSFI 17020-as parental lines in future breeding programs. For developing powdery mildew-resistant hybrids, inbreds, or varieties through marker-assisted backcrossing, ORS 684 is proposed as an effective foreground marker to facilitate the transfer of resistance loci.