Improvement of Continuous Deficit Irrigation Efficiency on Young Plum Tree Using Arbuscular Mycorrhizal Fungi

This work aimed to improve the efficiency of continuous deficit irrigation (CDI) on plum tree through using symbiosis with arbuscular mycorrhizal fungi (AMF). Thus, an experiment was conducted in pots to evaluate the effects of arbuscular mycorrhization on the growth of young plum trees, in two cases of CDI (50% and 75% of full crop evapotranspiration - ETc) compared to full irrigation (100% ETc). We used a mixture of two mycorrhizal fungi species, Rhizoglomus intraradices and Funneliformis mosseae. The measurements concerned: 1) morphological parameters of the root system (total fresh weight, total dry weight, total volume and hairy root dry weight); 2) morphological parameters of aerial parts (primary shoot elongation, number of secondary shoots, trunk growth, leaf area, total fresh weight and total dry weight); and 3) nutritional status parameters (leaf phosphorus content and chlorophyll pigments content). Compared to full irrigation, the two CDI levels induced a significant decrease of hairy root percentage without significantly affecting total root weight and volume. The use of AMF enabled to limit this depressive effect because it stimulates root ramification, but this is effective only under moderate water stress (75% of ETc). Under this CDI regime, hairy root percentage has been enhanced by 87% in mycorrhizal plants comparatively to non-mycorrhizal plants. Water stress effects on vegetative growth were partially alleviated using AMF even under severe decrease of irrigation (50% of ETc): shoot elongation was higher for mycorrrhizal plants exceeding non-mycorrhizal ones by an average of 13%. AMF induced also a significant increase of phosphorus, nitrogen and chlorophyll pigments concentration in mycorrhizal plants. Thus, AMF significantly improves CDI efficiency on young plum tree, even at level of 50% of ETc. The observed improvements due to AMF were considerable under 75% of ETc, suggesting the possibility to adopt this CDI level associated with AMF to optimize deficit irrigation on young plants of this rosaceous under low water availability conditions.