Cultivar-dependent gene transfer into citrus using agrobacterium

Abstract

Florida’s citrus industry is currently under severe onslaught from two non-indigenous but now endemic pathogens causing the diseases huanglongbing (HLB) and citrus canker. None of the commercial cultivars are resistant to either disease, which result in severe losses to the industry. Genetic transformation of citrus, to incorporate gene(s) for disease resistance not found in citrus, is gaining importance due to the possibility of incorporating resistance to these diseases. In an effort to transform a large number of cultivars via Agrobacterium-mediated transformation, epicotyl explants of several citrus scion and rootstock cultivars were evaluated for their ability to incorporate transgenes into their genome. It was determined that genetic transformation effi ciency depended on cultivar studied, and the cultivars were either relatively easy to transform, moderately diffi cult, or recalcitrant to Agrobacterium infection. In general, of the cultivars investigated, Carrizo and ‘Duncan’ had the highest transformation effi ciency (over 40%), followed by ‘OLL8’, a ‘Valencia’ like somaclone, and ‘Hamlin’ (20% to 40%). Poncirus trifoliata, ‘Marsh’ and ‘Flame’ grapefruit, and ‘Valencia’ sweet orange were moderately diffi cult (10% to 20%), while ‘Mexican Lime’, ‘Volkamer’ lemon, Citrus macrophylla, and tangerines were recalcitrant (less than 10%). Our results also suggested that fi nal recovery rate of transgenic plants suitable for transfer to a greenhouse were signifi cantly lower than the total transgenic plants obtained after transformation since the cultivars also varied in their ability to regenerate after in vitro grafting.