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Powdery mildew is a constant threat to cucumber production in soilless systems requiring the intensive use of chemical fungicides to limit yield losses. However, the toxicity risks for the growers and the food safety issues linked to fungicide residues represent a major concern for crops with a frequent and extended harvest period, like cucumber, and create an urgent need of eco-friendly alternatives. The objective of this study was to assess the effectiveness of foliar and root applications of the rare sugar tagatose, against naturally occurring powdery mildew (Podosphaera xanthii and Golovinomyces cichoracearum) on cucumber plants grown in a soilless system under commercial-like greenhouse conditions. Foliar and root applications of tagatose reduced powdery mildew severity and incidence under conditions of low severity in untreated plants, but tagatose and the chemical standard strategy lost their effect in the control of powdery mildew when the disease severity was increasing steadily. The combination of sulphur with foliar applications of tagatose effectively reduced powdery mildew under high severity conditions. Overall, under high disease pressure, foliar and root applications of tagatose were more effective than the standard chemical treatment reducing powdery mildew disease incidence and severity. Foliar application of tagatose directly inhibited P. xanthii conidial germination. After root application, tagatose was translocated to the leaves guaranteeing a systemic protection with no accumulation in cucumber fruits. Root applications of tagatose represent a novel strategy for cucumber protection against powdery mildew and reduce fungicide applications.

Tagatoseis a rare sugar metabolised by a limited number of microorganisms that inhibits a large spectrum of phytopathogens. In particular, tagatose inhibitedPhytophthora infestansgrowth and negatively affected mitochondrial processes. However, the possible effects of tagatose onP. infestansmetabolism have not yet been investigated. The aim of this study was to analyse the impact of this rare sugar on the sugar metabolism inP. infestans, in order to better understand its mode of action. Tagatose inhibited the growth ofP. infestanswith a precise reprogramming of thecarbohydrate metabolismthat involved a decrease of glucose, glucose-1-phosphate andmannosecontent and β-glucosidase activity. The combination of tagatose with common sugars led to three different responses and highlighted antagonistic interactions. In particular, glucose partially attenuated the inhibitory effects of tagatose, while fructose fully impaired tagatose-mediated growth inhibition and metabolite changes. Moreover, sucrose did not attenuate tagatose effects, suggesting that the inhibition of sucrosecatabolismand the alteration of glucose-related pathways contributed to the growth inhibition caused by tagatose toP. infestans. The interactions of tagatose with the common sugar metabolism were found to be a key mode of action againstP. infestansgrowth, which may represent the basis for the further development of tagatose as an eco-friendly fungicide.

Reduction of copper-based fungicides with the final aim of phasing out has a high priority in European policy as well as in organic agriculture. Our survey aims at providing an overview of the current use of copper-based plant protection products in European organic agriculture and the need for alternatives to allow policy makers to develop strategies for a complete phasing out. Due to a lack of centralized databases on pesticide use, our survey combines expert knowledge on permitted and real copper use per crop and country with statistics on organic area. In the 12 surveyed countries, covering together 83% of the European organically managed horticultural area, we calculated approximately 3258 t copper metal per year are consumed by organic agriculture, equalling to 53% of the permitted annual dosage. This amount is split between olives (1263 t y -1 , 39%), grapevine (990t y -1 , 30%), and almonds (317 t y -1 , 10%), followed by other crops with much smaller annual uses (-1 ). Potato, usually considered a highly demanding plant for copper inputs, only uses 39 t y -1 of copper per year. In 56% of the allowed cases (countries × crops), farmers use less than half of the allowed amount, and in 27% less than a quarter, with some variability between countries. Considering the large volumes of copper used annually, replacement of copper seems only feasible if all preventive strategies from the crop protection pyramid are fully implemented and several affordable alternative plant protection products are successfully brought to the market.

The study of the interactions among microorganisms, especially between pathogens and other microorganisms, is a very useful way to identify possible biocontrol agents (BCAs). In this study we verified the capability of δ(13)C analysis using isotope ratio mass spectrometry (IRMS) to detect active parasitism or metabolic assimilation of (13)C-labeled Armillaria mellea (plant pathogen) by Trichoderma atroviride and Pseudomonas fluorescens (two BCAs).The three microorganisms were labeled in pure-culture using a specific medium to which D-glucose (13)C was added. The δ(13)C analysis of mycelia/cells and DNA was undertaken using IRMS at different times, to study the uptake kinetics of (13)C. The mechanisms of interaction were studied by implementing dual-culture tests and measuring the δ(13)C values of the two BCAs after 29 days of contact with the labeled pathogen.A. mellea absorbed (13)C more slowly (plateau at 21 days) than T. atroviride and P. fluorescens (3 and 1 day, respectively) in pure-culture. The maximum δ(13)C values were higher in A. mellea and T. atroviride mycelia (8,019.9‰ and 10,383.7‰, respectively) than in P. fluorescens (953.4‰ in cells). In dual-culture the mycelia of T. atroviride which remained in direct contact with labeled A. mellea showed an increased δ(13)C value with respect to the unlabeled treatment (66.4‰ and -26.6‰, respectively), due to active interaction. Lower assimilation of (13)C was detected in P. fluorescens.This work demonstrates that IRMS can be used for the in-depth study of direct parasitism and interaction process between biocontrol agents and labeled pathogens, allowing the screening of potential new BCAs.