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.

白粉病是无土系统中黄瓜生产的持续威胁，需要大量使用化学杀菌剂来限制产量损失。然而，种植者的毒性风险以及与杀菌剂残留相关的食品安全问题是黄瓜等收获期频繁和延长的作物的主要关注点，迫切需要环保替代品。本研究的目的是评估稀有塔格糖的叶面和根部应用对天然白粉病（Podosphaera xanthii 和 Golovinomyces cichoracearum）的有效性) 在类似商业温室条件下在无土系统中生长的黄瓜植物。在未经处理的植物中，在低严重度条件下，塔格糖的叶面和根部施用降低了白粉病的严重程度和发病率，但当疾病严重程度稳定增加时，塔格糖和化学标准策略在控制白粉病方面失去了作用。硫磺与塔格糖的叶面施用相结合，有效地减少了严重条件下的白粉病。总体而言，在高病害压力下，叶面和根部施用塔格糖比标准化学处理更有效，可降低白粉病的发病率和严重程度。叶面喷施塔格糖直接抑制P. xanthii分生孢子萌发。根应用后，塔格糖被转移到叶子上，保证了系统保护，不会在黄瓜果实中积累。塔格糖的根应用代表了黄瓜防止白粉病和减少杀真菌剂应用的新策略。