Yanitsa Ilieva, Saurabh Gupta, Michael Wittenberg, Valentina Ivanova, Petar Kazakov, Saleh Alseekh, Neerakkal Sujeeth, Tsanko Gechev
Raspberry fruits are a healthy food rich in fibre, vitamins, minerals and antioxidants. Raspberries, however, are vulnerable to climate change effects. In particular, heat stress combined with solar radiation leads to white drupelets disorder: appearance of white spots on the fruits, making raspberry fruits unusable. We report that treatment of raspberry plants with a seaweed-based biostimulant, derived from the brown algae Ascophyllum nodosum , prevents the heat-induced sunburn, significantly reducing the number of damaged fruits and the number of white spots caused by the heat stress. Fruits from the biostimulant-primed raspberries were larger and the yield was higher. Comprehensive RNA-seq transcriptional analysis of biostimulant treated and untreated raspberries revealed that the biostimulants treatment induced genes related to auxin signalling and cell wall related proteins including expansins and extensins, supporting the notion that the biostimulant positively regulates growth. Genes encoding proline metabolic process, response to lipids and lipid biosynthetic processes, regulation of pH, and magnesium ion transport were also induced. At the same time, the A. nodosum -based biostimulant suppressed expression of genes encoding heat shock proteins and other stress related proteins. Downregulation of these genes provided molecular confirmation of the lower stress status of fruits collected from the biostimulant-treated plants. Metabolome analysis performed by GC/UHPLC-MS revealed that the fruits collected from biostimulant treated plants had up to three-fold higher levels amino acids, higher levels of the dipeptides HisAsp and ThrAla, and higher content of anthocyanins, two flavonoid glycosides, and Vitamin C. Overall, this demonstrated that the A. nodosum -based biostimulant prevented heat-induced sunburn and lead to production of fruits with higher concentrations of essential nutrients and health promoting metabolites, suggesting additional health benefits for the raspberry consumers.