The incidence of calcium oxalate crystals in fruit walls of tomato (<i>Lycopersicon esculentum</i>Mill.) as affected by humidity, phosphate and calcium supply

Abstract

In tomato fruit walls, around the calyx and shoulders of the fruit, tiny yellowish spots are often present, so-called gold specks. Fruits with many gold specks have a reduced shelf life. High humidity and high calcium fertilizer supply resulted in more gold specks, which is consistent with the observed higher inflow of Ca into the fruit. Increased phosphate supply also promoted gold specks appearance through increased plant uptake of Ca, although it is not clear why P supply increased Ca uptake. X-ray diffraction showed the crystals to be a mixture of CaC2O4, H2O and CaC2O4,2H2O, with the dihydrate form in only small amounts. Consequently gold specks can be considered as symptoms of Ca excess.