ISHS Acta Horticulturae 564: IV International Symposium on Mineral Nutrition of Deciduous Fruit Crops
NITROGEN, CELL WALLS AND TEXTURE OF STORED COX'S ORANGE PIPPIN APPLES |
| Authors: | D.S. Johnson, C.J. Dover, T.J. Samuelson, I.M. Huxham, M.C. Jarvis, L. Shakespeare, G.B. Seymour |
| Keywords: | Malus domestica, urea, calcium nitrate, sprays, mechanical properties |
| Abstract:
Sprays containing urea or calcium nitrate were applied repeatedly to Cox's Orange Pippin apple trees during the cell division (early) or cell expansion (late) phases of fruit growth. Nitrogen (N) concentration in the fruit at harvest was increased by early and late sprays of urea and by early sprays of calcium nitrate. Only late sprays of calcium nitrate increased the calcium (Ca) concentration in the fruit. In apples from controlled atmosphere (CA) storage, electron energy loss spectroscopy (EELS) was used to determine local N and Ca elemental intensity ratios relative to total carbon (C) in the primary cell wall (PW) and middle lamella (ML) regions in tissue prepared to preserve the elements in their native state. Both types of spray applied late in fruit development increased the N/C ratios in the ML and PW but they had no affect on the Ca/C ratios. Increases in the N/C ratios in the cell walls were associated with increased resistance to failure in compression and wedge-fracture tests performed on cortical tissue extracted from CA-stored apples. Late sprays of calcium nitrate also improved harvest and ex-store fruit firmness as measured with an automated penetrometer, a device relevant to the commercial evaluation of firmness. Additional benefits of calcium nitrate application included greater retention of a green background colour and a reduced incidence of bitter pit and rotting in CA-stored fruit. A negative effect of the treatment was the development of lenticel damage on the fruit. Further work is required to ameliorate this damaging effect of the calcium nitrate application. Results of these experiments support suggestions that cell wall proteins might play a significant role in determining texture in apples. | |
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