Variation in phenol colour reaction in grains of rice (Oryza sativa L.) varieties

Phenol colour reaction on grains and glumes is used for characterization of rice varieties for distinctiveness, uniformity and stability (DUS) testing in plant variety protection. According to DUS test guidelines, rice varieties are classified into two groups based on presence and absence of phenol colour reaction on the grains. However, rice grain changes to black or light brown colour in different frequencies in seed lots of varieties. An investigation was conducted to differentiate 20 rice varieties based on variations in phenol colour reaction. Studies were also conducted to show intra-panicle and inter-plant and panicle variation in paddy seeds based on the variation in phenol colour response during different seed growth and maturity stages. The results showed a negligible existence of inter-and intra-plant/panicle variation in grain in rice varieties due to phenol colour reaction. The phenol colour reaction starts at the post fertilization stage of the spikelet and is maintained in the matured grains. Instead of two groups the phenol colour test in the existing DUS test guidelines a higher number (five) of groups like black, dark brown, brown, light brown and no colour is recommended as a grouping characteristic in DUS testing of rice varieties for plant variety protection.