Rootstocks modulate the physiology and growth responses to water deficit and long-term recovery in grafted stone fruit trees

The effects of climate change have forced to search quickly new strategies to achieve sustainable agriculture in the context of a growing demand for food. Rootstocks have shown to have a key role in the resistance and tolerance to biotic and abiotic stresses in horticultural and fruit trees species, being a way to incorporate these strengths to the cultivated varieties. Here, we report the assessment of physiological parameters and growth responses of two commercial interspecific hybrid Prunus rootstocks contrasting in their tolerance to water deficit: 'ROOTPAC (R) 40' (tolerant) and 'ROOTPAC (R) 20' (sensitive); grafted with the almond cultivar Non Pareil or the Japanese plum cultivar Angeleno. Plants were subjected during 35 days to two irrigation treatments, well-watered and water deficit (drought period), followed by a recovery period of 44 days. On each period, biomass accumulation, stomatal density, water-use efficiency at the whole plant level and root hydraulic conductivity were determined in both irrigation treatments. Also, in the drought period, the fraction of transpirable soil water when the relative transpiration drops and the expression of seven aquaporins belonging to plasma membrane intrinsic proteins subfamily was assessed. In the drought period, 'ROOTPAC (R) 20' had a decrease in the aquaporin gene expression in roots and also had an early decline in transpiration, independent of the grafted scion. Also, on this rootstock, the biomass was more severely affected. On the other hand, 'ROOTPAC (R) 40' induced a late decline in transpiration and increased the water-use efficiency, keeping less affected the biomass accumulation. Contrasting with the above, in the recovery period, 'ROOTPAC (R) 20' improved the water-use efficiency, reaching higher biomass accumulation in the grafted plants. Also, we observed some interesting interactions between rootstocks and scions. 'ROOTPAC (R) 20' induced a higher stomatal density in both, almond and plum scions, and 'Angeleno' plum induced a bigger root hydraulic conductivity in both rootstocks, in comparison to almond 'Non Pareil', in the drought period.