1959 Volume 28 Issue 1 Pages 45-51
Although the double flowering tetraploid petunias are worthy of high admiration due to the typical gigantium of their attractive large flowers and plants growth, their available value for the popular growing is sometimes changed or decreased by the other various genetical and physiological peculiarities with which are endowed them on account of chromosomal doubling. For instance, fairly later flowering habit and exceedingly lowered seed productability of the tetraploids are almost inevitable events and are considered to be inexcusable demerits for economical culture. So in order to explain their main peculiar characteristics regard to the double- and singleness, size and coloring of flowers, and also, to seed productability by self-and cross-polli- nation, the experiments were carried out in 1955-1957, and the results were discussed as follows.
(1) As the double flowering character (D) is assumed to be monogenic dominant against recessive (d) in the diploid state, tetraploid plants of DDDD, DDDd, DDdd and Dddd-typed, which were produced by crossing with various typed parents of different genic constitutions, are all expected to be double flowering naturally. However, it was found in the experiments clearly that the more number of the single flowering plants than expected theoretically appeared always in the hybrid seedlings mixed with DDDd, DDdd, Dddd and dddd-typed. The cause is now explained conveniently by the assumption that about 27% of Dddd-typed plants transgressed to single flowering owing to the overwhelming of three minor recessive ddd genes against one major D. So the all-double strains were obtained only by cross- ing between Dddd or dddd and homo-double DDDD parents. (2) The size of flowers, together with double and single, showed the wide range of segre-gation from 6 to 14 cm in diameter in all hybrids: of various combinations. Then the colors of a most of flowers in the experiments indicated the compli-cated segregation modes showing redish-purple, magenta, carmine, red, rose and pink in accordance with differences of parental combinations, and ex-ceptionally, it was confirmed that salmon color was. perhaps recessive against the above-described ones. and bred true well. (3) It was one of the most striking facts of the induced autotetraploids that the-seed production decreased remarkably to about 10 and, more percentages of that of the ordinary diploids. The causes will be attributed to the two sources. The first one is the presence of higher-graded self-and cross-incompatibility strengthened by genic com-plication due to chromosomal doubling. And the second is the peculiar restricted adaptability of the autotetraploids for the environmental conditions, especially temperature, in the growing place. Name-ly, they necessitate the definite narrower and cooler temperature zone for getting good seed pro-duction than the corresponding diploids which, on the contrary, can raise up a much quantity of seeds in the condition of hotter and wider range of environ-mental temperatures. For example, the former requires 27_??_31°C zone for increasing pollen and seed fertility and the latter 28_??_33°C, signed as the maximum point of a day in the greenhouse at Utsu nomiya. These differences will be perhaps explain ed by supposing the presence of modifying minor genes regard to fertility which are much sensible. for temperature but inactive or recessive properly in the diploid state and become efficacious on modifying the fertility firstly when they are doubled in, the tetraploid constitution.
