POTENTIALS OF CALLUS CULTURE AS A BREEDING TOOL FOR POLYPLOIDISATION OF FRAGARIA VESCA L.

Abstract

Tunnel effects in 250 years of strawberry breeding history resulted in high performance cultivars with reduction in quality traits connected with flavour and resistances. Genetic resources for important traits are found in wild species such as Fragaria vesca. Mutation breeding of F. vesca up to an octoploid chromosome set is necessary for cross-breeding on a balanced ploidy level with Fragaria ×ananassa Duch. Here, we report on the treatment of axillary seedling buds with amiprofos-methyl (APM) which resulted in sectorial, mericlinal and periclinal ploidy chimeras. Chimeral segregation was performed via callus culture as well as using the generative way (selfing). Callus development and shoot regeneration on selected leaf segments depended on the composition of the medium and varied among the repetitions. The regeneration of adventitious shoots started after six to eight weeks on the induction medium and lasted four to six months. Evaluation of ploidy level was done by e.g., phenotype evaluation, comparison of leaf morphology, stomata measurement, flow cytometry and chromosome counting. From the mutagen treatment to the first fruits of the homohistic regenerates, a period of 18 months was sufficient via callus culture. For generative segregation a time span of 30 months was needed. More tetraploid plants were gained from callus culture than from generative segregation. The auto-tetraploid mutants do not differ in fertility and were used in test crosses with F. ×ananassa resulting in hexaploid hybrids. A second mutagen treatment is being executed to obtain auto-octoploids via polyploidisation of the tetraploid F. vesca.