The Influence of Fertilizer and Biostimulant Application on the Quality of Red Raspberry (Rubus Idaeus L.) Fruit in Continental Montenegro: Fruit Chemistry and Cultivar Response Under Climate Variability

The analysis of the effects of fertilisers, biostimulants, and climatic variability on the quality of red raspberry (Rubus idaeus L.) fruits is presented in this research. The research was conducted in Bijelo Polje, in northern Montenegro, which is characterized by mountainous continental climatic conditions. The research period was 2021-2023. In the experimental planting of raspberry cultivars: ‘Willamette’ and ‘Glen Ample’, seven treatments were applied: one control treatment; Four treatments with mineral fertilizer; Two biostimulant treatments. The chemical quality of the fruit was analysed, with parameters TSS, TS, TA, TSS/TA, and TS/TA, and also the vitamin C content. Variety, treatment, and year had significant effects. The ‘Willamette’ variety had a higher content of total sugars (up to 6.30%). The TS/TA ratio was more favourable (up to 8.52). This indicates better sensory quality and greater stability in changing climatic conditions. ‘Glen Ample’ variety is characterised by a higher content of total acids (up to 2.46%). The content of vitamin C is also higher (up to 54.43 mg 100 g⁻¹). This confirms its higher nutritional value. The best fruit quality was in 2023, when temperatures were accompanied by a more favourable water regime. Monoammonium phosphate (MAP) gave the best results with the variety ‘Glen Ample’. Treatments with phosphorus and potassium, together with biostimulants, were most effective with the variety ‘Willamette’. The results obtained confirm that raspberry fruit quality results from the interaction of genotype, nutrition, and climatic conditions, and emphasise the importance of adapting production technology to conditions of pronounced climatic variability.