Determination of in-Field Gene Flow Between Sugarcane Cultivars

Abstract

Genetically modified (GM) sugarcane is being developed for use in commercial production in several countries. Regulatory approval is required before these cultivars can be released and grown. Part of the approval process is to understand and assess the potential for environmental harm that might result from introduction of a GM organism. A key piece of biological information to assist in this analysis is to determine if and over what distance transgenes could be transferred by pollen from the GM plants and passed onto the next generation of sugarcane seeds. This is not known for sugarcane. Consequently, a field experiment was designed and conducted in Australia to determine the level of pollination between sugarcane cultivars (Saccharum spp. hybrids), and the distance over which it occurs, by placing non-GM flowering plants of cultivar Open image in new window in the centre of a field of non-GM cultivar Open image in new window . Mature inflorescences of the pollen receptor ( Open image in new window ) were collected in eight directions up to 200 m from the centre of the field. Parentage of the seeds from the mother plants germinating in controlled conditions was determined by molecular markers. At a distance of 1 m in all directions from the pollen source, relatively high levels of hybridisation were found, though this was highest (100%) in the upwind direction. The level of hybridisation decreased in the shape of an exponential decay curve but detectable levels of hybridisation still occurred at 200 m downwind from the pollen source. The high level of cross- pollination at close distance was confirmed in a second experiment. The potential for pollen to travel several hundred metres and effect pollination and the subsequent production of sugarcane seeds means that containment of a transgene by distance cannot be assumed for sugarcane. The potential for cross- pollination of sugarcane plants or of compatible, sympatric relatives will be dependent upon local conditions. The risk of harm as a result of pollen carrying a transgene subsequently pollinating and producing seed will have to be evaluated against the likelihood of germination and survival of the seed and the nature and effects of the transgene.