Abstract
The relationship between fruit quality and planting density (varying from 330 to 3178 trees·ha−1) was studied in 7- to 11-year-old ‘Starking Delicious’ apple trees (Malus domestica Borkh.) grafted onto M.9, M.26, M.7 and MM.106 and grown under a no-pruning system. On all rootstocks, fruit weight decreased as planting density (ρ) increased. The density effect on fruit weight (ω) was represented by ω = K1ρ−k1, where K1 and k1 depend on the relative solar radiation or light interception of the previous year, the current year and rootstocks. The watercore intensity index and soluble solids decreased as planting density increased, but flesh firmness increased. The density effect on watercore intensity index (μ), soluble solids (δ) and flesh firmness (ζ) was represented respectively by μ = K2exp(−k2ρ), δ = K3ρ−k3 and ζ = K4ρk4. The density effect on acidity (η) was represented by η = K5ρk5 for mature fruits, and η = K5ρ−k5 for immature fruits, and in these equations, when planting density for high-quality fruit production was set, an applicable equation was η = K5ρk5. K2, k2, K3, k3, K4, k4, K5 and k5 depend on the meteorological element in the canopy of the current year and rootstocks. These findings suggest that planting density for high-quality fruit production can be set using the equations described above, and that the high-quality fruit production capacity that set planting density possesses is demonstrated by harvesting when the fruit has reached the appropriate stage of maturity.
