RNAI Confers Resistance to Mosaic Virus in Sugarcane in the Field

Abstract

Genetic resistance is a fundamental tool to control sugarcane mosaic. The objective of this work is to validate the development of genetically engineered mosaic-resistant sugarcane in the field. Putatively transformed clones (events) generated by transforming five mosaic-susceptible donor genotypes with an RNAi construct targeting four mosaic virus groups were tested. One to 18 plants of each event grown in the greenhouse were mechanically inoculated with leaf extracts from SCMV (group SCE)-infected plants. Clones displaying no infected plants after 90 days as determined by mosaic-specific leaf printing immunoassays were transplanted to the field under natural infection conditions and selected for the absence of visible mosaic symptoms 85 and 140 days after planting. Selected clones were advanced to 4-m, single-row plots for further visual inspection for mosaic symptoms, and then to multiplication plots for seed increase. Selected clones were planted in replicated trials (3 x 10-m rows with four replicates) alongside uninfected controls and visually monitored for mosaic symptoms during three crop seasons. Out of 395 clones (3406 inoculated plants), 226 (1895 plants) advanced to the first field trial and were selected for the lack of visible mosaic symptoms after natural infection. Following this, 86 selected clones were planted in single-row plots after PCR confirmation of the presence of the transgene. Finally, nine transgenic clones were selected for the lack of mosaic infection as well as for agronomic traits and advanced to replicated field trials. Whereas mosaic infection was high in donor cultivars, no (5 clones) or low (4 clones) infection rates were observed in the transgenic events. Uninfected clones have remained virus-free for more than 11 years, and two events displayed improved cane yield when compared to the non-GM donor genotype. Further research is required to assess performance against different virus groups.