Use of a SCAR-based marker for the early detection of dwarf off-types in micropropagated Cavendish bananas

Abstract

A PCR-based marker, termed sequence characterised amplified region (SCAR), has been developed to allow a more robust and reliable method for detecting dwarf off-types in micropropagated Cavendish bananas, as compared to a RAPD marker (Damasco, et al., 1996). This SCAR-based marker allows for the early in vitro detection of dwarfs. It has also been used as an early guide to investigate the factors that promote genetic instability during micropropagation. Dwarf off-types can arise early in the multiplication process and were detected as early as the 4th subculture after initiation of shoot tips. The results also strongly indicated that adventitious shoot multiplication is the main factor contributing to the formation of dwarf off-types. Adventitious buds are promoted by higher concentrations of the phytohormone, benzylaminopurine (BAP), by splitting of propagules longitudinally during micropropagation and by preferentially selecting bulbil-like structures as propagules for further multiplication. The inherent instability of the cultivar being micropropagated was another major factor influencing the production of dwarf off-types. It was found that New Guinea Cavendish produced dwarfs at a higher frequency than Williams. Furthermore the dwarf off-types were more stable in vitro, and the conditions that favoured the induction of dwarfism in control plants did not favour reversion to normal plants in the dwarfs.