Farb- und Fruchtqualitätsverbesserung bei Äpfeln mit Monophosphat und Extenday

Monophosphates reportedly enhance red colouration of bi-coloured apple fruit by stimulating anthocyanin synthesis and, in addition with calcium or potassium, may improve fruit firmness; colour and firmness which may be restricted by the climate in Western Europe. 12-year-old cv. ‘Elstar’ apple trees at Klein-Altendorf near Bonn, Germany, were sprayed weekly with either of two monophosphates four weeks prior to harvest to improve fruit quality, i.e. colouration, sugar and firmness. White, woven reflective cloth was spread as an alternative on the grass strips between the tree rows six weeks prior to harvest for the same purpose. Untreated apple trees served as control. Neither of the three treatments affected fruit maturation, measured as Streif index. The monophosphate formulation containing calcium (Seniphos; 24% P₂O₅; 4% CaO; 2?×?10?L/ha) increased the sugar content of the cv. ‘Elstar’ apples in the outer as well as in the inner tree canopy and the reflective cloth additionally in fruit of the lower canopy close to the cloth's position on the ground. This white reflective cloth (Extenday) also affected fruit from the outer tree canopy with the largest sugar content (12.6°Brix) and firmness (7.6?kg/cm²) at harvest. The monophosphate formulation containing potassium (Rizammina 42; 8% P₂O₅, 21% K₂O; 3?×? 2.5?kg/ha) improved the category of greater 25% fruit colouration by only 3%. Both Seniphos and the reflective cloth increased this portion by 17–19%, thereby raising the portion of class-1-fruit by 8%, equivalent to additional earnings of 1,060 €/ha. The green ground colour of apples in the shaded inner canopy was retained by either monophosphate. In the well-illuminated tree periphery, however, the ground colour of fruit treated with either monophosphate was less green (more yellow-green) and the top colour was more red. The white reflective cloth induced the same positive effects on fruit colouration to a much larger extent. Both monophosphates increased fruit firmness after 4?months cold storage around 5% at a time when fruit were too soft for marketing as fresh products.