Inheritance and segregation of virus and herbicide resistance transgenes in sugarcane

Transgenic sugarcane parents containing multiple copies of herbicide resistance (bar) and Sorghum mosaic virus (SrMV) resistance (hut) genes were crossed with non-transgenic sugarcane varieties. Segregation of the transgenes in the progeny was determined using Southern blot analysis; herbicide resistance and SrMV resistance were assessed using bioassays. The segregation data were used to infer linkage relationships between transgenes in the parent plants. In two of the parents, all transgene insertions were linked in one position in the genome, although some recombination between insertion events did occur. In the third parent, insertion had occurred in two independent, unlinked loci. Analysis of progeny of this parent indicated that rearrangement or mutation occurred in both loci, resulting in non-parental transgene DNA fragments in some progeny. Most transgenic progeny containing the bar gene showed resistance to herbicide. SrMV inoculation indicated that a fairly high proportion of the transgenic progeny showed susceptibility. As the post-transcriptional gene silencing mechanism responsible for the virus resistance phenotype may be reset during meiosis, phenotypic screening of older plants may be a more reliable indication of virus resistance than screening young seedlings. This is the first report of transgene segregation in sugarcane, and we have demonstrated that transgenic sugarcane parents showing stable inheritance of transgenes can be effectively used in breeding programs.