Effects of selenium application with different combinations of secondary elements on 'Qingcui' plum leaf nutrition and fruit quality

Aims We aimed to identify the optimal combination of selenium (from Na2SeO4) and secondary elements required for obtaining the best nutritive characteristics and quality of 'Qingcui' plums. Methods Five treatments (Na2SeO4 with MgSO4 and CaSO4) and a control treatment without Se, Mg, Ca, or S were applied to 2-year-old 'Qingcui' plum trees in a greenhouse. Plum leaves and fruit were analyzed for color, nutrient, and quality characteristics during the growing and deciduous seasons as well as the following year. Results Leaf color parameters, pigment content, and specific weight significantly improved by CaSO4 addition during the growing and deciduous seasons. Ca and Mg contents during the growth, defoliation, and young leaf stages of the following year exhibited consistent trends under the different treatments, whereas Se and S contents differed according to the season and treatment. Thus, Mg and S showed high mobility and reutilization rates, whereas Ca and S showed poor mobility and reutilization rates. Leaf and fruit nutrient contents decreased in the order of Ca > Mg > S and S > Ca > Mg, respectively. The combination of 77 mg Na2SeO4, 10 g MgSO4, and 19 g CaSO4 yielded optimal fruit quality in terms of fruit weight, hardness, and soluble solids and fruit Se content. A large amount of Ca was present in the cell wall, whereas S and Mg were mainly observed as soluble components. Conclusions Our study revealed the best combination of Se and secondary elements leading to optimal leaf nutrition and fruit Se content and quality in 'Qingcui' plums.