Fruit Tissue Elements and Carotenoids in ‘Micro-Tina' Tomato Respond to Foliar Chelated Titanium

Titanium (Ti) is the ninth most abundant terrestrial element.  Average Ti concentration in plants is 1 mg/kg dry weight; however, large variations in Ti concentrations exist among different food crops due to differing regional soil and climatic conditions.  Titanium is non-toxic to humans and is often used in surgical and dental implants.  Food is the principal source of Ti in human diets, with an average intake of 300 to 800 µg Ti/day.  Even though Ti is poorly absorbed by plants, high concentrations can occur in food crops in localized areas.  Titanium exerts interesting influences on plant physiology.  Some research demonstrates Ti can be beneficial to plant growth at low concentrations, while higher Ti concentrations are very phytotoxic.  Recently, the beneficial effects of Ti have been described using the theory of “hormesis”.  Titanium uptake initiates defense responses in plants (increases in elemental uptake, production of secondary metabolites, and up-regulated antioxidant systems).  These defense reactions increase the health status of the plant and counteract any negative effects associated with increased tissue Ti.  Therefore, a study was undertaken to determine the impact of foliar applications of chelated Ti on quality factors in tomato fruits.  ‘Micro-Tina’ tomatoes (Lycopersicon esculentum Mill.) were grown in nutrient solutions and sprayed with a commercial chelated Ti.  ‘Micro-Tina' is a red-fruited, dwarf tomato cultivar with a short, compact growth habit.  A total of four foliar applications were made prior to flowering at 3 day intervals at concentrations of 0, 250, 500, and 1,000 mg Ti/L.  Fruit was harvested, graded and evaluated for yield, mineral nutrients, and carotenoid pigments.  Total fruit yield and weight of ripe fruits were not influenced by foliar Ti treatments.  Total fruit BRIX decreased with increasing foliar Ti treatments.  Foliar Ti did not influence fruit beta-carotene, or lycopene concentrations.  Fruit tissue lutein increased, then decreased in a quadratic response to increasing foliar Ti concentrations.  Fruit tissue Ti was below detection limits.  Calcium was the only element in the fruit to respond significantly to Ti treatments, increasing with Ti foliar concentrations.  Foliar applications of Ti to ‘Micro-Tina’ tomato influenced fruit tissue Ca and lutein concentrations; however, impacts on other fruit quality factors were minor.