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.
