ISHS Acta Horticulturae 92: Symposium on Mineral Nutrition and Fruit Quality of Temperate Zone Fruit Trees
INFLUENCE OF PHOSPHORUS SPRAYS ON THE STORAGE QUALITY OF APPLES |
| Author: | D.S. JOHNSON |
| Abstract:
The duration of the storage life of apples is inversely related to store temperature and, for many varieties, maximum life is obtained at -1 to 0°C, just above the freezing point (approximately - 2°C) of the tissue. However, both Cox's Orange Pippin and Bramley's Seedling develop low temperature breakdown (L.T.B.) when stored below 3°C and it may occur occasionally at recommended temperatures. Cool summers generally predispose fruits to L.T.B., particularly those containing relatively low concentrations of phosphorus. The effects of foliar applications of phosphorus have been investigated in East Malling trials. In preliminary screening the phosphorus concentration in Cox fruits was increased by orthophosphoric acid, monosodium dihydrogen phosphate, dipotassium monohydrogen phosphate, potassium dihydrogen phosphate and calcium tetrahydrogen diphosphate (all applied to give 0.2 per cent phosphorus) but the first three materials caused unacceptable amounts of lenticel injury. High volume (2250 l ha-1) sprays of the latter two materials increased fruit phosphorus concentration by 5.3 and 4.3 mg/100 g respectively and markedly reduced the severity of breakdown in controlled atmospheres (CA) (2 percent O2; 1 per cent CO2) at 1.5°C and 3.5°C. Potassium dihydrogen phosphate increased fruit potassium and the incidence of bitter pit at 3.5°C from 15 to 24 per cent whereas calcium tetrahydrogen phosphate promoted fruit calcium concentration and consequently reduced bitter pit (4 per cent). Foliar application (550 l ha-1) of triple superphosphate, calcium tetra-hydrogen diphosphate and mono-ammonium phosphate increased the phosphorus concentration in Bramley apples by 0.8, 1.2 and 1.1 mg/100 g respectively; the severity of breakdown (index of maximum 60) in fruits kept in 8–10 per cent CO2 at 1.5°C was 16, 19 and 18 respectively compared with 31 in the untreated. Bramley and Cox fruits with phosphorus levels below 9.0 mg/100 g and 11 g/100 g respectively may be at risk from L.T.B. in some years and, whilst supplementary phosphorus sprays may help offset this risk, there is little prospect of lowering recommended storage temperatures simply by raising fruit phosphorus levels. | |
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