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

The production of volatile organic compounds (VOCs) represents a promising strategy of plant-beneficial bacteria to control soil-borne phytopathogens. Pseudomonas sp. PICF6 and Pseudomonas simiae PICF7 are two indigenous inhabitants of olive roots displaying effective biological control against Verticillium dahliae. Additionally, strain PICF7 is able to promote the growth of barley and Arabidopsis thaliana, VOCs being involved in the growth of the latter species. In this study, the antagonistic capacity of these endophytic bacteria against relevant phytopathogens (Verticillium spp., Rhizoctonia solani, Sclerotinia sclerotiorum and Fusarium oxysporum f.sp. lycopersici) was assessed. Under in vitro conditions, PICF6 and PICF7 were only able to antagonize representative isolates of V. dahliae and V. longisporum. Remarkably, both strains produced an impressive portfolio of up to twenty VOCs, that included compounds with reported antifungal (e.g., 1-undecene, (methyldisulfanyl) methane and 1-decene) or plant growth promoting (e.g., tridecane, 1-decene) activities. Moreover, their volatilomes differed strongly in the absence and presence of V. dahliae. For example, when co incubated with the defoliating pathotype of V. dahliae, the antifungal compound 4-methyl-2,6-bis(2-methyl-2-propanyl)phenol was produced. Results suggest that volatiles emitted by these endophytes may differ in their modes of action, and that potential benefits for the host needs further investigation in planta.

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

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.

Assessing the Involvement of Selected Phenotypes of Pseudomonas simiae PICF7 in Olive Root Colonization and Biological Control of Verticillium dahliae.

Pseudomonas simiae PICF7 is an indigenous inhabitant of the olive (Olea europaea L.) rhizosphere/root endosphere and an effective biocontrol agent against Verticillium wilt of olive (VWO), caused by the soil-borne fungus Verticillium dahliae. This study aimed to evaluate the potential involvement of selected phenotypes of strain PICF7 in root colonization ability and VWO biocontrol. Therefore, a random transposon-insertion mutant bank of P. simiae PICF7 was screened for the loss of phenotypes likely involved in rhizosphere/soil persistence (copper resistance), root colonization (biofilm formation) and plant growth promotion (phytase activity). Transposon insertions in genes putatively coding for the transcriptional regulator CusR or the chemotaxis protein CheV were found to affect copper resistance, whereas an insertion in fleQ gene putatively encoding a flagellar regulatory protein hampered the ability to form a biofilm. However, these mutants displayed the same antagonistic effect against V. dahliae as the parental strain. Remarkably, two mutants impaired in biofilm formation were never found inside olive roots, whereas their ability to colonize the root exterior and to control VWO remained unaffected. Endophytic colonization of olive roots was unaltered in mutants impaired in copper resistance and phytase production. Results demonstrated that the phenotypes studied were irrelevant for VWO biocontrol.

Verticillium Wilt of Olive and its Control: What Did We Learn during the Last Decade?

Verticillium (Verticillium dahliae Kleb.) wilt is one of the most devastating diseases affecting olive (Olea europaea L. subsp. europaea var. europaea) cultivation. Its effective control strongly relies on integrated management strategies. Olive cultivation systems are experiencing important changes (e.g., high-density orchards, etc.) aiming at improving productivity. The impact of these changes on soil biology and the incidence/severity of olive pests and diseases has not yet been sufficiently evaluated. A comprehensive understanding of the biology of the pathogen and its populations, the epidemiological factors contributing to exacerbating the disease, the underlying mechanisms of tolerance/resistance, and the involvement of the olive-associated microbiota in the tree's health is needed. This knowledge will be instrumental to developing more effective control measures to confront the disease in regions where the pathogen is present, or to exclude it from V. dahliae-free areas. This review compiles the most recent advances achieved to understand the olive-V. dahliae interaction as well as measures to control the disease. Aspects such as the molecular basis of the host-pathogen interaction, the identification of new biocontrol agents, the implementation of "-omics" approaches to unravel the basis of disease tolerance, and the utilization of remote sensing technology for the early detection of pathogen attacks are highlighted.

The genus Datura L. (Solanaceae) in Mexico and Spain - Ethnobotanical perspective at the interface of medical and illicit uses.

ETHNOPHARMACOLOGICAL RELEVANCE: The different species of the genus Datura have been used traditionally by some pre-Columbian civilizations, as well as in medieval rituals linked to magic and witchcraft in both Mexico and Europe. It is also noteworthy the use of different alkaloids obtained from the plants for medicinal purposes in the treatment of various groups of diseases, especially of the respiratory and muscularskeletal systems. AIM OF THE STUDY: A review of the ethnobotanical uses of the genus Datura in Mexico and Spain has been conducted. We focus on the medicinal and ritualistic uses included in modern ethnobotanical studies, emphasizing the historical knowledge from post-colonial American Codices and medieval European texts. Datura's current social emergency as a drug of recreation and leisure, as well as its link to crimes of sexual abuse is also considered. The work is completed with some notes about the distribution and ecology of the different species and a phytochemical and pharmacological review of Datura alkaloids, necessary to understand their arrival in Europe and the ethnobotanical uses made since then MATERIALS AND METHODS: A literature review and compilation of information on traditional medicinal uses of the genus has been carried out from the main electronic databases. Traditional volumes (codices) have also been consulted in libraries of different institutions. Consultations have been made with the National Toxicological Services of Spain and Mexico for toxicological data. RESULTS: A total of 118 traditional uses were collected in both territories, 111 medicinal ones to be applied in 76 conditions or symptoms included in 13 pathological groups. Although there are particular medicinal uses in the two countries, we found up to 15 similar uses, of which 80% were previously mentioned in post-Colonial American codices. Applications in the treatment of asthma and rheumatism are also highlighted. Apart from medicinal uses, it is worth noting their cultural and social uses, in the case of Mexico relating to diseases such as being scared, astonishment or falling in love, and in the case of Spain, as a recreational drug and lately, for criminal purposes. CONCLUSIONS: This review highlights the variety of uses traditionally given to the different species in both territories. The fact that most of the coincident or similar uses in both countries also appear in the classical codices can be found an example of the flow, not only of the plants from America to Europe, but also of their associated information. It is also relevant that particular uses have derived in both countries, reflecting the difference in the cultural factors and traditions linked to rituals and cultural practices. Finally, the significant growth of Datura consumption in recent years as a drug of leisure and recreation, as well as in crimes of sexual submission, should be considered as research of maximum relevance in the field of forensic botany and toxicology.