Isolation of endophytic bacteria from wild plants in dry regions and investigation of their ability to promote plant growth and inhibit pathogenic fungi

In the dry regions environments such as Saudi Arabia, bacterial endophytes isolated from the roots and soil of healthy wild plants can promote plant growth by developing siderophores, phosphate solubilizing, Indole 3 Acetic Acid (IAA), and inhibit the growth of some plant fungal pathogens. This study aimed to isolate bacteria from wild plants in dry regions and to investigate their ability to be used as plant growth-promoting agent and inhibit plant pathogenic fungi. More than ninety endophytic bacterial isolates associated with the leaves, roots, and soil of healthy wild plants were collected from different sites in the Qassim region, Kingdom of Saudi Arabia, with the aim of characterizing and testing for their ability to promote plant growth activities and inhibit plant pathogenic fungi. Seventy strains were shown to produce indole-3-acetic acid (IAA) and 45 isolates produced siderophores, with 16 of these exhibiting large amounts. Twelve isolates tested positive for phosphate solubilization, with two isolates (QUSA 66 and QUSA 91) exhibiting greater efficiency for phosphate solubility. Twenty-five isolates produced more than 100 µg mL-1 of IAA, with production ranging from 100.5 to 404.7 µg mL-1. Six of these bacterial isolates (QUSA 2, 7, 10, 29, 30. and 40) produced more than 200 µg mL-1. A wide spectrum of activities was noted within the pseudomonas strains, indicating promising plant growth-promoting potential (e.g., the isolates from Pulicaria crispa and Calligonum comosum). In vitro results against plant pathogenic fungi showed that fifteen of the bacterial isolates inhibited growth of fungal mycelia by producing wide antagonistic zones. The isolates QUSA 26, 27, 28, 36, and 87 were able to produce siderophores and IAA and to solubilize phosphate. In addition, these isolates delayed mycelium growth of some Fusarium, Rhizoctonia solani, Botrytis, and Stemphylium spp