Sustainable Mitigation of Alkaline Stress in Grapevine Rootstocks (Vitis spp.) by Plant Growth-Promoting Rhizobacteria

Practical use of plant growth-promoting rhizobacteria (PGPR) on plants under stress conditions remains elusive because most of the studies focused on merely evaluating the plant growth-promoting effects on non-stressed plants. This study focused on the effect of root inoculation of different PGPRs on the growth and physiology of grapevine rootstocks 41 B, 99 R and 140 Ru grown in soilless culture with elevated pH. The rootstocks in pots under glasshouse condition were inoculated with Agrobacterium rubi A18 and Bacillus subtilis OSU 142 bacteria in early spring. To increase the pH of growth medium, the plants were watered with 250 mL plant(-1) bicarbonate solution (840 g L-1 NaHCO3) four times (beginning at 3-4 cm shoot growth) with one-month interval during the vegetation. Along with the bicarbonate supplementation to growth medium, root rhizosphere pH increased from an initial value 7.76 to the final values between 8.10 and 8.26. Although the bacteria population decreased progressively, they were able to alleviate the negative effects of high pH by improving vegetative growth, leaf physiology and nutrient acquisition in many cases. The bacteria strains employed in this study can be recommended to support grapevine growth and physiology under alkaline conditions for a sustainable and environment-friendly viticulture.