Genetic Stability

When a gene is transferred or induced to change by physical or chemical agents in long-lived perennials such as fruit trees, it is essential that stable patterns of gene expression are maintained for long periods of time and, although fruit trees are normally vegetatively propagated, the T-DNA should also be heritable in the progeny. Several studies have been carried out on genetic stability and inheritability with marker genes (James et al. 1996) or with important genes for agronomic performance, such as rolABC in transgenic kiwi plants of both cvs staminate GTH and pistillate Hayward (Rugini et al. 1997; 2000a). After 12 years the staminate rolABC plants still maintain the same morphology and the offspring (transgenic staminate X normal pistillate) was transgenic in 50% of plants. The cherry rootstock Colt, transgenic for RiT-DNA which seems able to modify the scion vigour (Rugini and Gutierrez-Pesce 1999), showed the same stability after four years in the field (Rugini, pers. com.). Transgenic apricot for virus coat protein still maintains its tolerance to viruses after several years in the field (Laimer, pers. com.). A lot of work has been done in the USA by Scorza and co-workers on transgenic plants of Prunus domestica carrying plum pox virus coat protein (PPV-CP), gus and nptII genes. The expression has been stable in the greenhouse for over five years and the progeny produced from hybridisation of transgenic plants carrying plum pox virus coat protein inherited the transgenes and expressed it (Ravelonandro et al. 1997). One should note that in some cases the transgenic plants may require different agronomic management in the field to optimise the performance of the plants, that is, vigorous growth observed in kiwi rolABC plants may require less N₂ fertilisation to avoid pathogen attacks (Balestra et al. 2001) and maybe less water.