Development and Application of a Quantitative PCR Detection Method to Quantify Venturia oleaginea in Asymptomatic Olive (Olea europaea) Leaves

Olive leaf spot caused by Venturia oleaginea: An updated review

Olive leaf spot (OLS) caused by Venturia oleaginea is widespread in all olive-growing areas and continents, where can cause severe yield losses. The disease is often underestimated for the difficulty to reveal early leaf symptoms and for the pathogen-induced phylloptosis, which creates the illusion of healthy and restored plants. The present review provide updated information on taxonomy, pathogen life style and cycle, epidemiology, diagnosis, and control. Application of copper-based fungicides is the main method to control OLS. However, the regulation 2009/1107 of the European Commission include these fungicides in the list of substances candidates for substitution. It is therefore urgent to find alternative control strategies especially for organic agriculture. Among new approaches/strategies for controlling OLS, promising results have been obtained using nanotechnology, endophytic microbes, and biostimulants.

An Insight into an Olive Scab on the "Istrska Belica" Variety: Host-Pathogen Interactions and Phyllosphere Mycobiome

The olive tree is one of the most important agricultural plants, affected by several pests and diseases that cause a severe decline in health status leading to crop losses. Olive leaf spot disease caused by the fungus Venturia oleaginea can result in complete tree defoliation and consequently lower yield. The aim of the study was to obtain new knowledge related to plant-pathogen interaction, reveal mechanisms of plant defense against the pathogen, and characterize fungal phyllosphere communities on infected and symptomless leaves that could contribute to the development of new plant breeding strategies and identification of novel biocontrol agents. The highly susceptible olive variety "Istrska Belica"' was selected for a detailed evaluation. Microscopy analyses led to the observation of raphides in the mesophyll and parenchyma cells of infected leaves and gave new insight into the complex V. oleaginea pathogenesis. Culturable and total phyllosphere mycobiota, obtained via metabarcoding approach, highlighted Didymella, Aureobasidium, Cladosporium, and Alternaria species as overlapping between infected and symptomless leaves. Only Venturia and Erythrobasidium in infected and Cladosporium in symptomless samples with higher abundance showed statistically significant differences. Based on the ecological role of identified taxa, it can be suggested that Cladosporium species might have potential antagonistic effects on V. oleaginea.

Early Detection and Temporal Dynamics of Pratylenchus scribneri Infection in Potato Roots Determined Using Quantitative PCR and Root Staining

The root-lesion nematode, Pratylenchus scribneri, is a migratory endo-parasitic nematode that impacts potato production on a large scale. Effective management of this nematode requires an understanding of its population dynamics alongside early detection. Typically, the nematode population estimates are made from infested soil; however, considering the endo-migratory lifestyle of this nematode, it also is crucial to determine the nematode population residing inside the host roots. In this study, a SYBR green-based quantitative real-time PCR (qPCR) assay was developed for detection and quantification of P. scribneri in potato roots. The assay used a previously reported primer pair (ITS-2F/ITS-2R), and it proved to be specific and sensitive, detecting as low as 1/128th equivalents of a P. scribneri individual per 0.2 g of potato roots. The robustness of the assay was reflected in high correlation observed between the P. scribneri densities determined microscopically and the densities detected by qPCR in artificially inoculated (R² = 0.93) and naturally infected (R² = 0.73) root samples. A time-course experiment conducted in the greenhouse using qPCR detected P. scribneri in potato roots as early as 5 days after planting. The results correlated well with the microscopic observations (R² = 0.80) and were complemented further with root staining. Additionally, three P. scribneri reproduction peaks were observed during one 3-month growth cycle of potato. Overall, the assay developed in this study is specific to P. scribneri in DNA extracts of root tissue and allows early detection and understandings of reproduction timings of this important nematode of potato.