An early mutant was observed in 1978 in the well-known French inbred
line F7, within an ear to row nursery. Within the segregating progenies
from selfing, the results of countings quite clearly indicate that the
mutation has a Mendelian type of inheritance and it is recessive in the
F7 genetic background:
Measurements of plant height and leaf number are
in agreement with the significant gain of 8 days for silking, due to a
decrease of the internode number:
|Ear Height cm||Plant Height cm||Leaves Above Ear||Total Leaves||100 Kernel Weight gm||Silking Day|
|F7 N||29.8±1.7||76.7±3.1||3.7±1||13.4±2.0||35.2±1.0||20.8 July ± 1.6|
|F7 Early||25.3±1.7||65.7±1.5||3.1±0.3||10.3±0.3||28.7±3.0||12.5 July ± 3.4|
Standard errors are of the mean of 10 plants at P = 0.01 level; all measurements are significantly different at the 0.01 level.
Photoperiodic reaction will be tested to determine the physiological basis of the mutation. The decrease of the internode number seems to be different from that reported by Blanco (MGCNL 53:8-9, 1979), in which the similar decrease is associated with the pale green system pg11 pg12. No visual difference can be seen between normal and early F7 about chlorophyll content.
The usefulness is subject to the inheritance in different backgrounds. Because many genes are segregating, it seems difficult to compare the ranges of the F2 generations from F7 normal and F7 early crossed with each inbred line. In the breeding of conversion, the inheritance will be better known only after three backcrosses at a level of 93.75% homozygosity. These backcrosses will be made without intermediary selfings, taking from the different generations the earliest silking plants. In each generation of backcross and in each progeny, n plants have to be backcrossed. With a probability of 0.01 to lack one gene, n is computed from (1/2)n < 0.01. At the third backcross, i.e., for each 72 progenies 7 plants have to be backcrossed and then 343 plants have to be selfed. Another limitation is the decrease of yield correlated with the earliness increase, inasmuch as the kernel weight is affected.
M. Pollacsek and M. Caenen
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