Pineapple transformation: managing somaclonal variation

Abstract

A biolistics technique is now available for producing transgenic Smooth Cayenne pineapple plants. The regeneration system is based on the production of highly regenerable callus from leaf bases of in vitro grown plantlets. Approximately 90% of leaf bases produce callus within three months of initial culture and at least 90% of such callus pieces have proven regenerable upon transfer to a shoot regeneration medium. Multiple shoots can be readily obtained within four weeks. Bombarded calli are cultured on selective media containing geneticin, with monthly subcultures. After 3-4 months of culture transformed cells can be seen to grow and develop into healthy green tissue, while non-transformed tissue turns black and dies. The whole process, from establishment of in vitro plants to provide a source of explant material for callus initiation to glasshouse establishment of transgenic plants, takes from 2-3 years. Somaclonal variation was observed on transgenic plants in the glasshouse as indicated by the incidence of leaf spininess, which varied from 0-14%. This was not appreciably different from the incidence observed among non-transgenic, micropropagated plants. However Smooth Cayenne is known to produce a range of somatic mutations, including fruit defects, and the full extent of somaclonal variation in transgenic plants is not yet known.