Abiotic Stress at the Early Grain Filling Stage Affects Aromatics, Grain Quality and Grain Yield in Thai Fragrant Rice (Oryza sativa) Cultivars

2-Acetyl-1-pyrroline (2AP) plays an important role in determining the economic value of fragrant rice cultivars controlled by the Osbadh2 gene. However, the aromatic content of rice varies by cultivar and environment, especially under abiotic stress. Therefore, the objectives of this study were to investigate the effects of abiotic stress on the grain yield, 2AP content and grain quality of six fragrant rice cultivars exposed to abiotic stress, including drought (soil water potential -50 kPa), salinity (EC 10 +/- 0.5 ds m(-1)) and heat (40-42 degrees C daytime), compared to control conditions during the early grain filling stage for four consecutive growing seasons from 2019 to 2020. The results show that grain yield, 2AP content and grain quality were significantly different across cultivars, seasons and abiotic stress conditions. Pinkaset1 had the highest 2AP levels under control and abiotic stress conditions, followed by KDML105. Abiotic stress had a negative effect in decreasing grain yield, seed setting and grain quality, especially in amylose content. In contrast, drought and salinity stresses had a positive effect in increasing the 2AP content in grain. PTT1 and KDML105 had a higher percentage of 2AP than the other cultivars when compared to the control condition. In addition, the relationship between 2AP content and proline concentration was highly significant. In conclusion, drought and salinity conditions can stimulate higher 2AP levels. However, grain yield and seed quality were also reduced. Thus, fragrant rice should be cultivated in optimal environments with good cultural practices to balance grain yield with 2AP accumulation.