Grain level characterization of widely cultivating traditional and new improved rice ( Oryza sativa L.) varieties of Sri Lanka using physical and chemical test methods

Rice is the staple food over half of the world including Sri Lanka which has numerous rice varieties. Identification of Sri Lankan rice varieties (RVs) at the grain level is a great challenge due to its high diversity. Further, extremely limited research has been carried out on this topic to date. The present study aimed to characterize widely cultivating 10 traditional and 15 new improved RVs at grain level using internationally accepted physical and chemical test methods. Grain length and size were studied as physical tests (n = 5 each). Ferrous sulphate, phenol, modified phenol, NaOH and KOH tests (n = 4 each) were studied as chemical tests. Physical tests were able to group RVs into 4 groups as extra-long, long, medium and short grain rice. In contrast, chemical test methods, ferrous sulphate, phenol, modified phenol, NaOH and KOH tests were able to group RVs into 4 (no colour change, brown, strong brown and dark brown streaks), 5 (no colour change, strong brown, dark brown, reddish yellow and black), 5 (no colour change, strong brown, dark brown, dark reddish brown and black), 5 (pale yellow, yellow, olive yellow, light red and red) and 6 (pale yellow, yellow, olive yellow, light red, red and dark red) groups respectively. None of the physical or chemical test methods alone were able to characterize studied RVs at the grain level. The combination of both methods was able to cluster selected RVs into two main clusters (CI and CII) and was able to identify 3 RVs (Rathel, Suwadel and Kalu Heenati) at the grain level. It is concluded that the selected methods could be coupled with other varietal identification methods for grain level characterization of Sri Lankan rice.