ROLC strawberry plant adaptability, productivity, and tolerance to soil-borne disease and mycorrhizal interactions.

The potential to improve strawberry cultivation was assessed regarding the use the rolC genes from Agrobacterium rhizogenes that can confer higher levels of free cytokinins. Strawberry (cv. Calypso) rolC lines were produced by genetic transformation of Agrobacterium tumefaciens. Yield and fruit quality of the control and transgenic lines were measured under open-field conditions. The effects of the transgenic rolC lines depended on gene copy number: rolC lines with one (Line A) or two gene (Line B) copies showed 30% greater yields than controls, due to 20% more fruit per plant and an increased fruit weight. Line A also differed in terms of the highest fruit quality, due to 10.5% increased soluble solids and 12.7% higher acidity. Moreover, cv. Calypso rolC lines A and B had increased tolerance to greenhouse infection by Phytophthora cactorum. Conversely, for all of these characters, Line F (five rolC copies) was not significantly different from the control line. The same lines were also used to examine their symbiosis with root arbuscular mycorrhizal fungi (AMF) using vital and non-vital staining of roots collected at different stages of plant growth. Control and rolC plants showed similar intensities of AMF infection according to plant phenology and/or physiology. Furthermore, possible horizontal gene transfer of the rolC gene was tested for the AMF spores by PCR, with all AMF samples negative using rolC primers. The use of the rolC gene should be considered for the improvements provided in productivity, fruit quality and disease resistance of cultivated strawberry that show no effects on soil microorganisms.