Mutation breeding of Dahlia variabilis

Abstract

Tubers of a number of garden dahlia cultivars were irradiated with various dosages of X-rays. The optimal dose ranges from 2 to 3 krad, considering the production of rooted cuttings, the speed of rooting, the subsequent development of the young plants as well as mutation frequency. A great number of mutations for flower colour and shape were observed in the irradiated varieties "Salmon Rays", "Arthur Godfrey" and "Eldorado". Four mutants of "Salmon Rays" have been awarded, named, registered as new varieties and put on the market (see colour pictures and description in the text). The very quick results (the tubers were irradiated only three years ago, in November 1963) are largely due to the propagation method used in Dahlia. This method, taking a series of cuttings from the crown of the irradiated tubers, often results in mutated tissue taking part in the formation of new tubers, thus enabling the mutated character to be transmitted to the next vegetative generation. Alternatively one may consider the rooting of softwood cuttings after the observation of an interesting mutation and their propagation after the overwintering under suitable greenhouse conditions (temperature, long day). However, the usually high percentage of so-called "blind" tubers formed in the latter case, may give insuperable difficulties. The possibility of mutation induction in other cultivars of the octoploid garden dahlia strongly depends upon their genetic constitution. The complicated genetics and the great number of flower colour genes involved, make it difficult to predict which varieties may or may not give positive results.