third vegetative generation of a field-grown transgenic pineapple clone shows minor side effects of transformation on plant physiological parameters

Genetic modifications of pineapple provide the potential to increase fungal resistance without the use of pesticides. Previously, we developed a procedure for pineapple callus transformation, introducing the antifungal chitinase and AP24 genes, and the herbicide-tolerance conferring bar gene as a selectable marker. The three recombinant genes were under the control of the constitutively expressing promoters OCS-35S CaMV-rice actin I, 35S CaMV, and maize Ubi1, respectively. The objective of this study was to analyze whether these genetic modifications caused unintentional side effects on growth-related properties under field conditions. We analyzed the third vegetative generation of a transgenic pineapple clone, approximately 7 years after the genetic modification occurred. Plant height and diameter, chlorophyll and phenolic contents, fruit mass and D leaf (middle-age) mass, water content, succulence, sap pH, transpiration, CO₂ assimilation, and water use efficiency were recorded and compared to a micro-propagated cultivar. A macro-propagated variant was also cultivated at the field site in order to distinguish unintended effects of the propagation method from that of the genetic modification. While all parameters analyzed in this study were highly similar to each other for the three cultivars, statistically analyses revealed significant deviations of the genetically modified variant for the succulence index being higher at in the morning and evening, carbon dioxide assimilation being lower at noon and, at night, the water use efficiency was lower. The minor deviations were all within the range which can be expected between common cultivars grown together.