Evaluation of Indigenous Olive Biocontrol Rhizobacteria as Protectants against Drought and Salt Stress

Abstract

Stress caused by drought and salinity may compromise growth and productivity of olive (Olea europaea L.) tree crops. Several studies have reported the use of beneficial rhizobacteria to alleviate symptoms produced by these stresses, which is attributed in some cases to the activity of 1-aminocyclopropane-1-carboxylic acid deaminase (ACD). A collection of beneficial olive rhizobacteria was in vitro screened for ACD activity. Pseudomonas sp. PICF6 displayed this phenotype and sequencing of its genome confirmed the presence of an acdS gene. In contrast, the well-known root endophyte and biocontrol agent Pseudomonas simiae PICF7 was defective in ACD activity, even though the presence of an ACD-coding gene was earlier predicted in its genome. In this study, an unidentified deaminase was confirmed instead. Greenhouse experiments with olive ‘Picual’ plants inoculated either with PICF6 or PICF7, or co-inoculated with both strains, and subjected to drought or salt stress were carried out. Several physiological and biochemical parameters increased in stressed plants (i.e., stomatal conductance and flavonoids content), regardless of whether or not they were previously bacterized. Results showed that neither PICF6 (ACD positive) nor PICF7 (ACD negative) lessened the negative effects caused by the abiotic stresses tested, at least under our experimental conditions.

Identification of Volatile Organic Compounds Emitted by Two Beneficial Endophytic Pseudomonas Strains from Olive Roots

“…PICF6, is still very limited except for its effectiveness to antagonize V. dahliae in vitro and to control Verticillium wilt of olive (VWO) [ 28 ]. Interestingly, both PICF6 and PICF7 are able to colonize the interior of olive roots [ 39 , 40 ].…”

Sustainable Olive Culture under Climate Change: The Potential of Biostimulants

“…Greenhouse experiments with potted olive plants, cv 'Picual' (5-month-old), inoculated with Pseudomonas ssp. PICF6 and Pseudomonas simiae PICF7, together or individually improved the content of leaf flavonoids under drought and salinity stress [124]. Also, under salinity conditions (100 and 200 mM NaCl), the application of the amino acid proline to potted olive plants (2-years-old) enhanced stress tolerance by improving the leaf water status (leaf relative water content and water potential), upregulating the antioxidant enzymes (SOD, APC and CAT), enhancing the levels of chlorophylls, and improving the gas exchange parameters (photosynthesis, stomatal conductance and transpiration rate) [125].…”

Confronting stresses affecting olive cultivation from the holobiont perspective

“…However, better tolerance to salinity was not found in young olive plants inoculated with two different PGPMs (Pseudomonas sp. PICF6 and Pseudomonas simiae PICF7), regardless of whether (PICF6) or not (PICF7) they displayed ACD activity (Montes-Osuna et al, 2021b).…”

“…In vitro and in planta antagonistic ability against V. dahliae has been thoroughly investigated for P. simiae PICF7, an indigenous inhabitant of olive roots (Mercado-Blanco et al, 2004;Martıńez-Garcıá et al, 2015;Montes-Osuna et al, 2021a). However, no protective effect was found for this strain to mitigate drought and salt stress (Montes-Osuna et al, 2021b). Previously, this and other 28 strains of bacteria and fungi isolated from olive organs were tested for their in vitro antagonistic activity against V. dahliae (Varo et al, 2016) (Table 4).…”