Impact of a delayed senescence <i>OsSGR</i> allele on yield improvement in Milyang 374

Rice production faces significant challenges owing to increasing global demands and the adverse effects of climate change.To achieve stable and improved actual yields, breeding rice varieties with delayed senescence has emerged as a promising strategy.Therefore, this study aims to evaluate the performance of "Milyang 374", a near-isogenic line (NIL) derived from the Tongil-type rice "Milyang 21", which carries the OsSGR gene responsible for delayed chlorophyll degradation.Field trials were conducted from 2021 to 2023 in Miryang, from 2022 to 2023 in Sangju, and from 2023 in Cheorwon.In Miryang, yield was assessed under early, normal, and late transplanting schedules to evaluate the effect of different planting seasons.In Sangju and Cheorwon, yield performance was tested to assess adaptability across regions.The results showed that "Milyang 374" exhibited stable yield performance across different transplanting schedules and regions, achieving an average yield increase of 7.4% compared to that of "Milyang 21"."Milyang 374" demonstrated a higher 1,000-grain weight, averaging 21.6 g, than the 19.8 g in "Milyang 21", attributed to the presence of the OsSGR gene.This gene facilitated prolonged photosynthetic activity during the grain-filling stage, resulting in more effective carbohydrate accumulation.While the number of panicles and seeds per panicle was reduced, the delayed senescence trait contributed to higher grain filling rates and overall yield improvements.These findings highlight the value of incorporating stay-green traits in breeding programs to enhance yield stability and quality across different planting schedules and environmental conditions.