Loose packing of starch molecules results in black pin-point damage in Rice

Any rice variety to be released for cultivation to farmers should have acceptable grain quality, besides being high yielding. Black pin-point damage appears as small black spot on the milled rice grains which reduces the yield of milled rice and directly reflects on consumer acceptability. The black pin-point damage beyond the permissible limit set by Food Safety and Standards Authority of India (FSSAI) regulations, resulted in withdrawal of a very high yielding variety, PAU 201 released by Punjab Agricultural University in 2008. The damage has been later seen in high yielding rice genotypes PR 125 and PR 126 at Punjab Agricultural University, Ludhiana. Both PR 125 and PR 126 are the introductions from International Rice Research Institute (IRRI), Philippines, of which PR 126 was released for commercial cultivation having advantages of high yield, short duration with minimal black pin-point damage intensity. To understand the genetics of this trait, the black pin-point damage intensity was studied in F₃ seeds of crosses PR 121 x PR 125. The percentage intensity of damage was 0.61 g ± 0.06 damaged grains with range of 0.32–1.1 g in twenty different samples. The percentage intensity of damage was 2.48 ± 0.22 with the range of 1.28–4.44 in PR125 and 2.03 ± 0.05 with a range of 0.5–5.1 in 256 F₃ individuals. The black pin-point damage followed continuous distribution showing quantitative inheritance of trait. The anatomical evaluation of damaged grains using scanning electron microscopy (SEM) showed the malformation of starch granules at cellular level. The starch granules of damaged grains at the site of damage were loosely packed as compared to the normal grains. However, no sign of pathological infestation was observed at the site of damage on the grains. The analysis of transverse section of the point of damage demonstrated that the black pin-point was embedded inside the grain. These observations indicate that black pin-point might be due to loose packing of starch granules at the site of damage and deformities in the genes involved in starch packing could be the possible reason for development of this trait.