Potassium nutrition increases the lycopene content of tomato fruit

To determine the influence of potassium levels in the nutrient solution on lycopene content, tomato plants were grown in a soil-less system using rockwool slabs as substrate. Two growing seasons were studied with the aim of comparing three potassium levels: low, medium and high (corresponding to 150, 300 and 450 mg K l–1 in the nutrient solution). In the first growing season (Spring–Summer), two high-pigment cultivars of tomato (Solanum lycopersicum L.,‘SVR’ and ‘Kabiria’) were compared. In the second growing season (Summer–winter) ‘Esperanza’, a non high-pigment hybrid and the two previous cultivars were used. Total fruit yield was higher in the Summer–Winter growing season than in the Spring–Summer season, but was not influenced by potassium nutrition. Growing season, potassium level, and the genetic traits of the cultivars influenced the principal quality parameters of fruit, with higher dry matter and total soluble solids contents in the first growing season, correlating with lower lycopene and K+ contents in the fruit. The lycopene content increased linearly with increasing potassium level in the nutrient solution. The high-pigment genotypes showed a higher lycopene content than ‘Esperanza’.The higher lycopene content in ‘Kabiria’ fruit can also be related to the size of the fruit.