Biostimulant applications to mitigate multiple summer stress effects on potted Corylus avellana L. young plants

In the current scenario of decreasing in precipitation and water resources, and increasing in temperature,   it is pivotal to define multiple strategies to cope with the negative consequences on the crop production and food security. Hazelnut (Corylus avellana L.) is an important nut tree crop grown in several countries all over the world and mainly in the Mediterranean Basin area. Among the producer countries Italy is the second main worldwide producer, soon after Turkey. Despite the long-lasting and traditional cultivation of hazelnut in the hilly areas and a recent wider spread of its orchards to newly cultivated fertile plains, hazelnut is well known as a very sensitive species to both water stress and high temperatures. The main aim of this study was to evaluate growth performances and morpho-physiological adaptive responses to prolonged water stress in potted young hazelnut plants. Secondarily, the effect of biostimulant treatments in mitigating the effects of water and heat stresses were evaluated. The research was conducted on one-year-old cultivar micro propagated plants of cv “Tonda di Giffoni” grown in a cold polycarbonate greenhouse at the Department of Agricultural Sciences of the University of Naples “Federico II” during two consecutive growing seasons. Three irrigation levels (i.e. 100, 80, and 60% of the daily water requirement) were applied in combination with two different biostimulant treatments. In particular, they consisted in the application near the roots of protein hydrolysate or mycorrhizae inoculation. The first one was applied every two weeks with a dosage of 2.5 ml/l according to the chemical characteristics of the product, during the whole growing season; instead, the second one was applied with a single-dose of 15 g per plant at the beginning of each growing season. During the two seasons, growth rate (i.e. basal diameter, branch length, leaf number, leaf area, and buds), eco-physiological behaviour (i.e. gas exchanges measurements, Chlorophyll a fluorescence emission, SPAD index, and leaf water potential), and leaf functional traits were investigated. Results   showed that the use of biostimulant and mycorrhizae positively influenced physiological behaviour and growth of plants by counteracting deficit irrigation stress effects. In conclusion, our study demonstrate how these type of treatments help to improve the quality of plants.