IN-VIVO GLYCEMIC INDEX (GI) AND HERITABILITY OF SELECTED, IMPROVED AND TRADITIONAL RICE VARIETIES CULTIVATED IN SRI  LANKA AND THEIR CORRELATION WITH IN-VITRO MODEL  

Sri Lanka’s rice productivity, crucial for food security, faces scrutiny over cultivation trends.  While traditional rice varieties (TRVs) are praised for health benefits, 99% of cultivation  focuses on new improved varieties (NIVs) for higher economic returns. Research often suffers  from sample errors, lack of variety comparisons, and overlooked milling effects. To address these gaps, a comprehensive study was designed, incorporating popular TRVs, NIVs, and old  improved and exotic varieties (OIVs, ERVs). The study aimed to evaluate heritability and key morphological, nutritional, physicochemical, and nutraceutical traits, providing a balanced  analysis of rice cultivation practices. The study evaluated 40 rice varieties (red and white pericarp, short to long grains) in research fields at Rice Research Station, Ambalantota over two seasons (2018/19 Maha, 2019 Yala) using RCBD with three replicates. Seedlings were nursery-grown and transplanted at 15x15 cm spacing. Traits assessed included physicochemical (amylose, gelatinization), nutritional (protein, fat, fiber), antioxidants (DPPH, FRAP), and glycemic characteristics (in vivo glycemic index, in-vitro digestion) through standard protocols. Ethical clearance was obtained for glycemic studies involving healthy adults. Heritability estimates were calculated using standard methods. Rigorous protocols ensured accuracy, including pre-trials, seed purity checks. The study revealed significant variations in the morphological, agronomic, physicochemical, nutritional, and antioxidant traits of 40 rice varieties. NIV outperformed TRV in key agronomic traits such as plant height (PH), tillering (NT), leaf area (LA), panicle length (PL), number of grains per panicle (NGP), and thousand-grain mass (TGM). NIVs’ moderate height, erect leaves, sturdy culms, and lodging resistance enhance their yield potential. Despite the availability of over 2,000 TRVs and 93 NIVs, a few NIVs (e.g., At 362, Bg 352, Bg 300, Bw  367, Bg 360, Bg 94-1, Bg 358) dominate cultivation in Sri Lanka, accounting for 99% of the area due to high yield, lodging resistance, and superior milling quality. Physicochemical traits influencing cooking and sensory qualities varied widely. GT affects cooking time and texture, with TRVs showing high to intermediate GT linked to higher A). AC ranged from 17.0% to 31.3%, with TRVs generally having higher AC, preferred for their non-sticky texture. NIVs such as At 405 and At 306 cater to Basmati-like rice demand with low to intermediate AC. Protein content ranged from 5.19% to 8.4%, with higher levels in varieties like H4 and Bw 272-6B. TRVs like Rath Suwandel and NIVs like Ld 368 had higher fat content. High ash content, indicating mineral richness, was observed in Bw 272-6B. Negative correlations were noted between carbohydrate content and nutrients like protein, fat, and ash. Pigmented rice varieties exhibited significantly higher antioxidant levels, with varieties like Masuran, Nonabokra, and Kaluheenati being antioxidant-rich. Antioxidant levels decreased during milling and cooking, with losses up to 96%, but varieties like Bw 272 6B and At 311 retained high levels post-cooking. Pigmented rice with reddish-yellow pericarp showed strong antioxidant potential regardless of grain type or origin. The glycemic index (GI) ranged from 44.5 to 82, with most varieties classified as medium GI. Low-GI varieties were limited to NIVs; TRVs showed no low GI. Glycemic load (GL) depended more on serving size and cooking methods than genetic traits.  In-vitro starch readings exceeded in-vivo GI, with an insignificant correlation (p≤0.05) between them, highlighting the need to refine in vitro protocols. High heritability (H²) for agronomic, amylose, crude fiber, crude ash, and antioxidant traits indicates strong genetic improvement potential, while low H² for GI confirms its reliance on external factors. The findings highlight the need to balance grain yield and nutritional quality in rice breeding programs. Varieties like Bw 272-6B excel in both, meeting consumer demands affordably. Sri Lankan preferences focus on sensory qualities, cooking characteristics, and health benefits. Promoting less-milled pigmented, high-GT, and low-GI rice can improve diets and reduce non-communicable disease risks. Branding rice based on these traits and consumer education are vital for diversifying consumption. Integrating superior TRVs into breeding programs and promoting demand-driven cultivation can enhance rice quality, ensure food security, and  address niche markets. Varieties like At 362, Bg 300, and At 311 show promise for balancing  productivity with nutraceutical and sensory benefits, supporting sustainable production and  consumption.