Crop Load Influences Fruit Quality, Nutritional Balance, and Return Bloom in 'Honeycrisp' Apple

The apple variety, 'Honeycrisp' has been extensively planted in North America during the last two decades. However, it suffers from several agronomic problems that limit productivity and postharvest quality. To reduce losses, new information is needed to better describe the impact of crop load on productivity and postharvest fruit quality in a desert environment and the major region where 'Honeycrisp' expansion is occurring. Here, 7-year-old 'Honeycrisp' trees on the M9-Nic29 rootstock (2.5 x 0.9 m) were hand thinned to five different crop loads [from 4.7 to 16.0 fruit/cm(2) of trunk cross-sectional area (TCSA)] to compare fruit quality, maturity, fruit size, elemental concentration, and return bloom. Fruit size distribution was affected by crop load. Trees with the highest crop load (16 fruit/cm(2)) produced smaller fruit. Index of absorbance difference (I-AD) measurements (absorption difference between 670 and 720 nm), a proxy indicator of the chlorophyll content below the skin of fruit measured by a DA-meter, were made shortly after harvest (T0) and after 6 months of storage (T1). Fruit from the trees with the lowest crop load had lower I-AD values indicating advanced fruit ripeness. The comparison between the I-AD classes at T0 and T1 showed that fruit belonging to the lowest I-AD class had significantly higher red blushed overcolor percentage, firmness, dry matter, and soluble solid content than those in the "most unripe" class (highest I-AD readings) regardless of crop load. The percentage of blushed color, firmness, titratable acidity (TA), soluble solids content, and dry matter were all higher in the lowest crop loads at both T0 and T1. Fruit calcium (Ca) concentration was lowest at the lowest crop load. The (K + Mg + N):Ca ratio decreased as crop load increased until a crop load of 11.3 fruit/cm(2), which was not significantly different from higher crop loads. For return bloom, the highest number of flower clusters per tree was reported for 4.7 fruit/cm(2) crop load, and generally it decreased as crop load increased. Here, we highlight the corresponding changes in fruit quality, storability, and elemental balance with tree crop load. To maintain high fruit quality and consistency in yield, careful crop load management is required to minimize bienniality and improve fruit quality and storability.