Somaclonal variation in insect-resistant transgenic sugarcane (Saccharum hybrid) plants produced by cell electroporation

A population of 42 transgenic sugarcane ( hybrid, cv. Ja60-5) clones expres sing a truncated cryIA(b) gene from Bacillus thuringiensis was evaluated in field trials under artificial borer (Diatraea saccharalis Fab.) infection. Five clones displaying the highest borer tolerance were selected and analy sed with molecular tools (RAPD, AFLP and RAMP) to verify genomic changes. R esults of field trials provided evidence both for the expression of the res istance trait and for the occurrence of limited but consistent morphologica l, physiological and phytopathological variation, as compared with control plants regenerated from dedifferentiated culture without transformation (C1 -control) or with plants that were clonally propagated in the field (C2-con trol). The five elite transgenic clones, selected for consistent borer-resi stance and good agronomic traits, were further evaluated in a large scale f ield trial. It was found that the majority of agronomic and industrial trai ts were those of the original cv. Ja60-5, but that a small number of qualit ative traits was different. DNA changes were verified in the five selected clones. A total of 51 polymorphic DNA bands (out of the 1237 analysed bands ) was identified by extensive AFLP and RAMP analysis, thus showing rare but consistent genomic changes in the transgenic plants, as compared with C1- and C2-control plants. It is proposed that the increased variability verifi ed in transgenic plants by field trials and DNA analysis is essentially cor related with cell growth in the dedifferentiated state during the transform ation procedure. The results, which are consistent with those published in the case of other transgenic plant populations, are discussed in the contex t of selecting approaches to gene transfer that minimize somaclonal variati on. This is important especially in cases, such as that of sugarcane, where success of backcrosses to restore the original genotype is made difficult by the complex ploidy state of the plant.