Inoculation with isolates of arbuscular mycorrhizal fungi influences growth, nutrient use efficiency and gas exchange traits in micropropagated apple rootstock ‘Marubakaido’

Apple rootstocks establish symbiosis with arbuscular mycorrhizal fungi (AMF), however the influence of fungal isolates on nutritional and physiological parameters are limited. The aim of this work was to evaluate the growth, nutrient uptake and use efficiency, and gas exchange of apple micropropagated rootstock ‘Marubakaido’ inoculated with four isolates of AMF with differing levels of phosphorus (P). We grew plantlets in a non-sterilized soil inoculated with AMF isolates Acaulospora colombiana SCT115A, A. morrowiae SCT400B, Claroideoglomus etunicatum SCT101A, and Gigaspora albida SCT200A, plus a non-inoculated treatment at three levels of P (0%, 50% e 100%). After 90 days of AMF inoculation, internal CO 2 concentration ( ci ), transpiration rate ( E ), stomatal conductance ( g s ) and photosynthetic rate ( A ) were evaluated and after 315 days, total dry biomass, macro and micronutrient contents and mycorrhizal colonization were determined. AMF inoculation, regardless of P levels, decreased ci , E and g s , and increased the intrinsic water use efficiency (A/gs) and water use efficiency ( A/E ). The total biomass results differed among the AMF isolates, where G. albida stood out increasing apple rootstock growth in all levels of P. Gigaspora albida also increased the relative accumulation of N, K, Ca, Mg, Cu and B and had lower mycorrhizal colonization rates. Nutrient use efficiency was higher in plants inoculated with G. albida compared to control plants. In conclusion, although the AMF isolates demonstrated positive results depending on the soil P concentration, we found evidence that G. albida has the potential to be used as inoculant on apple rootstock ‘Marubakaido’ production in nurseries to enhance tree performance.