EFFECTS OF PHOSPHATE SPRAYS ON McINTOSH APPLE FRUIT AND LEAF COMPOSITION, FLESH FIRMNESS AND SUSCEPTIBILITY TO LOW-TEMPERATURE DISORDERS

Abstract

Phosphate compounds (NH4H2PO4, KH2PO4 and CaH4(PO4)2 in 1982; NH4H2PO4 in 1983) applied to McIntosh apple trees as six foliar sprays at weekly intervals starting 4 wk after bloom, increased leaf and fruit P, decreased loss of firmness under some storage conditions and decreased incidence of low-temperature storage disorders. Phosphate sprays improved firmness retention of apples stored in either 5% CO2 plus 3% O2 or 0.7% CO2 plus 1% O2 in 1982 and maintained fruit firmness during a simulated shelf life at 20 °C for apples stored at 0 °C. Firmness retention at 20 °C of the 1983 crop was improved by monobasic ammonium phosphate regardless of storage temperature. Apple samples from unsprayed control trees had mean phosphorus concentrations of 85.4 and 94.4 ppm fresh weight in 1982 and 1983, respectively (whole fruit less seeds and stems).Key words: Apple, fruit phosphorus, low temperature breakdown, core flush