Mutation breeding of Chrysanthemum morifolium Ram. using in vivo and in vitro adventitious bud techniques

Summary During experiments, which are being carried out to study the factors which control the process of adventitious bud formation in vivo on detached leaves of Chrysanthemum morifolium Ram, adventitious shoots were produced from leaves, irradiated with 500 rad of X-rays. The most important but disadvantageous result was that the majority of the adventitious shoots proved to be of a chimeral nature and obviously developed from more than one cell.An in vitro adventitious bud technique was developed using different types of explants. Pedicel segments regenerated the highest number of adventitious shoots and, moreover, they developed faster as compared to explants of young flower heads or leaves. The mutants produced by irradiating the various explants were almost exclusively of a solid (non-chimeral) nature. In addition, histological observations suggest that single epidermal cells are involved in the initiation of the adventitious shoot apices.The optimum dose for mutant production is approximately 800 rad X-rays. Rather often, more than one phenotypically identical mutant was found, which was always derived from the same explant. They could for instance originate from a multi-apical meristem formed by a single mutated cell.     

Mutation breeding of chrysanthemums

Rooted cuttings of the pot-grown Chrysanthemum variety Hortensien Rose were irradiated with X-rays, fast neutrons, thermal neutrons and electrons. As soon as the plants grew they were topped to stimulated side-shoot formation, often resulting in complete periclinal chimeras (sports). In addition mutation frequency in a given number of plants is enlarged by such a method.Electrons proved to be ineffective, producing only 6–10% mutated plants. The optimum dose X-rays is 1500 Rads. Both fast and thermal neutrons showed a marked higher mutation frequency, the best dose resulting in both cases in c. 28% of mutated plants.The mutation spectra, e.g. the type of mutations induced, showed some variation after the various treatments. But the number of plants irradiated, as well as the number of mutations induced, do not justify the conclusion that a certain treatment results in a specific mutation spectrum, although there was a tendency towards greater variability after neutron irradiation.The mutation spectrum as well as the frequency greatly depends on the genetic constitution of the treated material. Irradiation of the pink-flowering Hortensien Rose, with the maximum number of dominant genes for flower colour, resulted in a great number of different flower colours, as was expected, as well as a number of mutations of flower shape and size. Other pink-flowering varieties showed a similar spectrum, although in some cases the frequency was low or even zero. Chrysanthemum varieties with other flower colours showed a lower mutation rate, most of the flower colour mutations being based on a lower number of dominant genes.Finally, the practical importance and ways of application were discussed.     

Mutation breeding of Kalanchoë

Summary Freshly detached leaves of Kalanchoë cv. Annette and Josine were irradiated with X-rays and then planted to root and to produce adventitious plantlets. The age of the leaf, the presence or absence of the petiole as well as the genotype proved to be important factors in the production of adventitious plantlets.In Kalanchoë only solid, non-chimeral mutants were observed which indicates that the apex of the adventitious plantlets may originate from a single cell. This observation agrees with similar results in Achimenes, Saintpaulia, Streptocarpus and other species, where only a very small fraction of the mutants consisted of chimeras.The mutations observed were changes in flower colour and size, time of flowering, type of inflorescence, leaf form, size and colour, plant habit and other directly visible characters.A few promising mutants, selected by commercial plant breeders, are being propagated and will be evaluated.     

Mutation breeding of Alstroemeria

Summary Actively growing young rhizomes of various Alstroemeria cultivars, most sterile hybrids, were treated with X-rays. The optimum dose was about 400 rad for diploid cultivars and 500–600 rad for triploid ones.Although the buds on the rhizomes most certainly have multicellular apices, no X-ray mutant showed any sign of chimerism. Hence only solid(-looking) mutants were obtained. This phenomenon, an unforeseen but advantageous circumstance, could not be explained.Among the rather large number of mutants, several proved to be improvements and have been released to the trade such as cvs. Canaria Stagula, Yellow Tiger Stavero, White Wings Staretto, Harmony Stabroza and Rosita Stareza.     

The use of an in vitro adventitious bud technique for mutation breeding of Begonia x hiëmalis

Summary An in vitro propagation of two genotypes of Begonia x hiëmalis was achieved through adventitious shoot formation on (sub)cultured leaf-disc explants and subsequent transplantation to soil of explant-parts with adventitious shoots.After irradiation of detached leaves with different doses of X-rays and two cycles of adventitious shoot formation on in vitro (sub)cultured leaf-disc explants, plantlets were produced. About 30% of these plants was mutated with respect to e.g. the colour, size and form of the leaves and flowers. The great majority of the mutants (98.5%) proved to be solid (non-chimeric).     

Mutation breeding of Achimenes

Summary Freshly cut leaves of Achimenes cv. Paul Arnold were irradiated with X-rays or fast neutrons, or treated with colchicine and then allowed to root and form adventitious buds. As found previously in Saintpaulia and Streptocarpus, almost exclusively solid, non-chimeral mutants or tetraploids were, respectively, obtained by using the adventitious bud technique, demonstrating that the apex of such buds originates from single cells.Although the heterozygosity of the original material apparently was not large, a relatively wide mutation spectrum was observed among the mutants produced.After comparative judging, three mutants were awarded a Certificate of Merit and have been commercialized.Two of these are earlier flowering mutants (Early Arnold and Spring time), the third having a more compact form (Compact Arnold).     

A mutant of a mutant of a mutant of a...: Irradiation of progressive radiation-induced mutants in a mutation-breeding programme with Chrysanthemum morifolium Ram.

Summary Radiation-induced sports in Chrysanthemum morifolium Ram. have been reported for several years. It has become an everyday practice to produce flower-colour mutants from outstanding cross-breeding products, even before they are distributed for the commercial production of cut flowers.One of the most successful and recent examples is that of cv. Horim, of which hundreds of mutants were produced by successive use of radiation-induced mutants in the mutation-breeding programme. Over about 4 years a variety of flower-colour mutants was obtained, not only largely including the outstanding characteristics of the original cultivar but sometimes even with an appreciable improvement in quality and yield. It is expected that the latter types, the Miros group, will soon completely supersede the spontaneous or radiation-induced Horim sports and mutants and take over the leading position of the Horim group in the production of all-year-round (AYR) cut flowers.     

Is DTT a means to improve the mutation spectrum of vegetatively propagated plants?

Summary Freshly detached leaves of Achimenes cv. Cupido were placed, with their petioles, into a solution of DTT (dithiothreitol) during one or more hours, prior to irradiation with X-rays or fast neutrons. The radioresistance increased considerably, requiring a doubling of the X-ray dose to obtain the same survival and production of rhizomes as with non-pretreated leaves. The protection against fast neutrons was less. The mutation frequency decreased after pretreatment with DTT, though more drastically with X-rays than with fast neutrons. It seems that, in comparison with non-pretreatment of leaves the relative number of drastic mutants (supposedly caused by gross chromosome aberrations) hardly deviates significantly when leaves are pretreated with DTT, both after X-rays and fast neutrons; i.e. no improvement of the mutation spectrum has been obtained.