Micropropagated walnut dependency on phosphate fertilization and arbuscular mycorrhiza for growth, nutrition and quality differ between rootstocks both after acclimatization andpost-acclimatization

Abstract

AbstractThe English walnut (Juglans regiaL.) is the main species cultivated for the production of edible nuts.In vitromicropropagation of walnut explants, necessary for mass propagation of high-quality walnut rootstocks, needs anex vitroacclimatization phase followed by apost-acclimatization growth in greenhouse when plantlets become photoautotrophic. However, poor survival and slow growth rates are common difficulties encountered in nurseries when establishing micropropagated walnut saplings. As many other fruit and nut bearing trees, walnut exhibits a high dependency on symbiotic soil-borne arbuscular mycorrhizal fungi for better soil nutrient acquisition and development due to a coarse root architecture that notably limits soil inorganic phosphate (Pi) uptake. In the context of rootstock production, we investigated the establishment of seven walnut rootstocks of economic interest (RG2, RG6, R17, RX1, VLACH, VX211, and WIP3) inoculated or not withRhizophagus irregularisunder two contrasting Pi fertilization regimes. We demonstrated that inoculation withR. irregularisdecreases micropropagated walnut rootstock dependency on Pi fertilization both at the acclimatization andpost-acclimatization stages, together with improving quality, sapling biomass production and nutrition of walnut rootstocks. We also showed that these benefits are rootstock-dependent, indicating that walnut mycorrhizal dependency for Pi nutrition varies between cultivars.