Estimation of the number of initial cells in panicle primordia of the rice embryo

Abstract

An attempt is made to estimate the size of the mutated sector in Mj panicles and number of initial cells constituting the various panicle primordia in the rice embryo. Normal plants from M,, progenies segregating with a deficit on recessive mutants were carried forward to the M^ generation of plant progeny basis. The data from segregating M3 progenies derived from the same M1 panicle were pooled and the mean Ma ratio for each progeny was calculated. The M3 ratios were generally higher than the corresponding M, ratios. The size of the mutated sector of the M1 panicle was estimated by dividing the Ma ratio in each progeny by the corresponding Mj ratio. The number of initial cells was obtained as the reciprocal of the sector size. Variation in the size of the mutated sector and number of initial cells was exhibited by panicles of the categories. For the apical ear the size of the sector was from 0.08 to 0.45 and number of initial cells from 2 to 12. The sector size in the primary ears ranged from 0.33 to 1 .00 and the number of initial cells from 1 to 3. The secondaries of primaries 2, 3 and 4 have originated from 1 to 2 initial cells. The primary and secondary ears of a primary group might have originated from the same set of initial cells in the embryo. Deficit of recessive mutant was found in the Ma generation of all categories of panicles. This deficit in a generation later than the M2 is attributed to genetic or zygotic eliminations. Since the apical panicle has more number of initial cells and consequently smaller mutated sector, it is necessary to grow a large progeny to recover a mutation induced in its primordium.