Figure 1. PGP strains have a cross-efficacy in promoting drought resistance in different plant models. (A) Representative images of the promotion effect on the root system of pepper plants inoculated with R05ACCd and R16ACCd strains⁶ and field-grown for 2 months under irrigation-limited conditions, compared with the uninoculated control (labeled with “no bacteria added”). Bar = 10 cm. (B) Pepper root fresh weights determined on the plants of the experiment in (A). Values are means of 4 plants ± standard deviations. The P values according to the student t-test are indicated to evaluate the differences between the plants treated with bacteria and the non-treated controls. (C) B-O strain, isolated from the rhizosphere of an olive tree growing in South Tunisia, was used to inoculate tomato plants (3 plants for each treatment). After re-watering, following a 10-d induced drought by withholding irrigation, tomato plants treated with B-O strain exhibited an increase of root fresh biomass compared to untreated control. (+): uninoculated plants, properly supplied with water during the experiment; (-): uninoculated control plants subjected to drought; (B-O): plants treated with B-O isolate and subjected to water stress. (D) B-G strain, isolated from the root endosphere of Barbera plants, was used to inoculate SO4-grafted grapevine plants (5 plantlets for each treatment). After re-watering, following a drought event induced by reducing water irrigation to 50% of water holding capacity, grapevine plants treated with B-G strain exhibited an increase of grapevine fresh biomass compared with untreated control. (+): uninoculated plants, properly supplied with water during the experiment; (-): uninoculated control plants subjected to drought; (B-G): plants treated with B-G isolate and subjected to water stress. *: P ≤ 0.05 according to the student t-test.