Bioprotection of Olive Trees Against Verticillium Wilt by Pomegranate and Carob Extracts.

Bioprotection using plant extracts is an environmentally friendly strategy in crop protection. Effective control of Verticillium wilt of olive (Olea europaea; VWO), caused by Verticillium dahliae, has proven challenging due to the ineffectiveness of chemicals, which makes it necessary to search for new control tools. Thus, the aim of this study was to evaluate the effect of pomegranate (Punica granatum) and carob (Ceratonia siliqua) extracts against VWO. Extracts derived from pomegranate peels and carob pods and leaves were obtained using ethanol, methanol, or ethyl acetate as solvents. A targeted analysis of their metabolite composition was performed using QTRAP Ultra High-Performance Liquid Chromatography with Mass Spectrometry (QTRAP UHPLC‒MS). Remarkably, gallic acid was detected in all extracts at a high concentration. The effect of the extracts on the mycelial growth and on the germination of conidia and microsclerotia of V. dahliae was evaluated by in vitro sensitivity tests at various doses: 0 (control), 3, 30, 300 and 3,000 mg of extract/liter. Extracts obtained with ethanol or methanol significantly reduced the viability of V. dahliae structures when applied at the highest dose, while those obtained with ethyl acetate were ineffective across all doses. The most effective extracts, as determined in vitro, were then evaluated against the disease in olive plants. Potted plants of cv. Picual were treated by spraying (foliar application) or irrigation (root application) of extracts at 3,000 mg of extract/liter, followed by inoculation with V. dahliae. The results indicated that foliar applications were ineffective, while root treatments with pomegranate peel or carob leaf extracts were more effective in reducing disease severity, regardless of solvent, compared to that of the untreated control.

Effect of Cultivar Resistance and Soil Management on Spatial-Temporal Development of Verticillium Wilt of Olive: A Long-Term Study.

Verticillium wilt, caused by Verticillium dahliae, challenges olive cultivation and an Integrated Disease Management (IDM) approach is the best-suited tool to combat it. Since 1998, an IDM strategy in an orchard (called Granon, Spain) of the susceptible cv. Picual was conducted by increasing planting density with moderately resistant cv. Frantoio, chemical weed control, and replanting of dead olives with cv. Frantoio following soil solarization. The Verticillium wilt epidemic in Granon orchard was compared to the epidemic in a non-IDM orchard (called Ancla, Spain) with plowed soil and dead Picual olives replanted with the same cultivar. Field evaluations (2012-2013) showed an incidence and severity of the disease as Picual-Ancla > Picual-Granon > Frantoio-Granon. The spatiotemporal dynamics of the Verticillium epidemics from 1998 to 2010 were monitored with digital images using SIG. The annual tree mortalities were 5.6% for Picual olives in Ancla orchard, and 3.1 and 0.7% for Picual and Frantoio olives in Granon orchard, respectively. There was a negative relationship between the mortality of olive trees (%) by the pathogen and the height (m) above sea level. The annual mortality of cv. Picual olives was positively correlated with spring rainfalls. The Index of Dispersion and beta-binomial distribution showed aggregation of Verticillium-dead olives. In conclusion, this IDM strategy considerably reduced the disease in comparison with traditional agronomic practices.

Differences Between Ascospores and Conidia of Didymella rabiei in Spore Germination and Infection of Chickpea.

ABSTRACT Studies were performed to compare the germination and infection of ascospores and conidia of Didymella rabiei under different temperature and moisture conditions. Germination of ascospores and conidia on cover glasses coated with water agar began after 2 h, with maximum germination (>95%) occurring in 6 h at 20 degrees C. No germination occurred at 0 and 35 degrees C. Ascospores germinated more rapidly than conidia at all temperatures. Germination declined rapidly as the water potential varied from 0 to -4 MPa, although some germination occurred at -6 MPa at 20 and 25 degrees C. Ascospores germinated over a wider range of water potentials than conidia and their germ tubes were longer than those of conidia at most water potentials and temperatures. The optimum temperature for infection and disease development by both ascospores and conidia was around 20 degrees C. Disease severity was higher when ascospores were discharged directly onto plant surfaces from naturally infested chickpea debris compared with aqueous suspensions of ascospores and conidia sprayed onto plants Disease severity increased as the length of the wetness period increased. When dry periods of 6 to 48 h occurred immediately after inoculation, disease severity decreased, except for the shorter periods which had the opposite effect. Disease severity was higher with ascospore inoculum when no dry periods occurred after inoculation.

Identity and Pathogenicity of Two Phytophthora Taxa Associated with a New Root Disease of Olive Trees.

Fifty-two Phytophthora isolates from necrotic roots of olives were characterized. Colony morphologies on carrot-agar medium led us to separate them into two groups: A (36 isolates) and B (16 isolates). The optimum growth temperature for Group A was about 21°C, with slow growth at 30°C. In contrast, Group B isolates had an optimum temperature for growth of 26°C, and grew rapidly at 30°C. Growth rates, sporangial and oogonial characteristics of the Group A isolates conformed to P. megasperma "BHR-type" sensu stricto. This designation was supported by a sequence analysis of their ITS rDNA regions. Colony patterns, sporangial characteristics and temperature-growth relationships of the Group B isolates conformed closely to those of the 'O-group' taxon of Phytophthora. They also conformed to this unusual taxon in their ITS sequence. In addition, Group B isolates were either entirely self-sterile, self-sterile A1s or weakly self-fertile. Pathogenicity tests showed that both taxa were highly aggressive on roots of olive trees. The association of flooding with Phytophthora infection indicates that the previously reported high sensitivity of olive to root asphyxiation may be more properly regarded as root-rot caused by Phytophthora spp.