Genetic Analysis of Pigmentation in a Cultivar of Rice (Orilzu sativa Linn)
Two cultivars of Oryza sativa Linn. were studied for the mode of inheritance of pigmentation of their organs. The studies show that purple leaf blade is conditioned at two loci in such a way that the inhibitor locus must be homozygous recessive for the purple leaf blade gene. Pl to express (ii Pl.). The collar colour is also controlled by the Pl gene. The coloured state of the apiculus, awn, stigma and outer leaf sheath are conditioned by a single dominant gene. The situation is however different for the auricle and ligule which are conditioned by recessive genes at their respective loci. The inner leaf sheath colouration is under the control of two independent genes in complementary action. The Pl gene exhibited manifold pleiotropic effect on all the organs except the inner leaf sheath whose colour it inhibits. The colour of the sterile lemma is due exclusively to the pleiotropic action of the Pl gene. The gene for apiculus colour (Pa) is a major gene which acts as a basic gene for colour expression in the inner leaf sheath acting in complementary mode with gene (Psh) and the organs of the juncture complex – ligule and auricle – which can express colour only when the genes that condition colour in them are present in addition to the gene Pa for purple apiculus colour. Gene Pa, in the homozygous recessive condition is therefore said to be epistatic to the colour genes for the auricle and ligule. Gene Pa also expresses manifold pleiotropic effect on the stigma, awn, nodal ring and outer leaf sheath. This is precisely why this gene is considered the most reliable marker gene of the entire genic system considered. The contribution of pleiotropic action of the various genes was estimated to be between 100% and 22%.