Herbicide-tolerant sugarcane (Saccharum officinarum L.) plants: an unconventional method of weed removal

Unnecessary weed growth in sugarcane fields forces plants to compete for nutrients and sunlight for survival, which most often leads to significant yield losses. As chemical herbicides cannot differentiate between crop plants and weeds, the development of herbicide-tolerant crops is anticipated. Four sugarcane varieties, CPF-234, CPF-213, HSF-240, and CPF-246, were used to develop glyphosate herbicide tolerance. A glyphosate-tolerant gene of 1368 bp cloned directionally under the 35S promoter with the beta-glucuronidase (GUS) reporter gene was used as the transgene. Through the biolistic transformation of sugarcane, calli of all cultivars were transformed with glyphosate-tolerant gene constructs. Efficient regeneration conditions were optimized on 1.5-2.5 mg/L kinetin, 1.5-2.5 mg/L 6-benzylaminopurine (BAP), and 1 mg/L gibberellic acid (GA(3)). The transformants exhibited the best shoot regeneration on a medium containing 2 mg/L kinetin, 2 mg/L BAP, 2 mg/L GA(3), and 1 mg/L indole-3-acetic acid. Based on initial screenings through GUS assay, the transformation efficiency was 22%, 32%, 17%, and 13% for cultivars 246, 234, 213, and 240, respectively. In transformed sugarcane plants, the transgene of 1368 bp was amplified. ELISA with gene-specific coated monoclonal IgG confirmed the transgene protein expression. It was revealed that all acclimatized transgenic sugarcane plants survived the glyphosate spray application of 900 mL/0.404 ha, except for the control nontransformed plants. However, at spray application of 1100 mL/0.404 ha, transgenic plants having the transgene protein OD of 0.2 to 1.0 did not survive, while those that had a transgene protein OD range of between 1.0 and 2.0 did. In addition, weeds growing alongside transgenic sugarcane plants turned brown and subsequently died at glyphosate spray applications of both 900 and 1100 mL/0.404 ha.