DRIFT IN GENETIC STABILITY IN MICROPROPAGATION: THE CASE OF STRAWBERRY

Abstract

Genetic stability during micropropagation is controlled by numerous factors. Among the internal plant factors, the genotypes, the presence of chimeral tissue and mainly the explant origin, play an enormous role, Moreover, some external factors as the tissue culture protocol, media sequences and the growth substance concentration, have also an important influence on genetic stability. In micropropagated strawberry plants, sporadic occurrences of abnormal fruit setting, with a hyper-flowering habit, were observed in some cultivars, always after numerous subcultures. Therefore, it was arbitrarily decided in 1980 to limit the number of subcultures to ten. In 1990, it was hypothesised that the hyper-flowering habit was related to and connected with the development of special buds, called stipular-buds, These always arise from a specific position on the leaf petiole and show an abnormal phyllotaxy, a very high propagation rate in vitro and a large number of flowers per inflorescence ex vitro. The hyper-flowering habit is unlikely to be due to true mutations, but rather to a reproducible event, possibly DNA methylation. The occurrence of these stipular-buds is reduced by decreasing the benzylaminopurine (BAP) concentration from 1 to 0.5 or 0.2 mg 1 -1 depending on the genotype. It is also necessary to limit the propagation to ten subcultures.