Enhancement of Tomato Fruit Lycopene by Potassium Is Cultivar Dependent

The purpose of this experiment was to determine the response of tomato ( Solanum lycopersicum L.) cultivars with fruit of average and high lycopene to increased K fertilization. The field experiment was designed as a factorial, split-plot, randomized complete block with four replications. The main plot consisted of K rates ranging from 0 to 372 kg·ha −1 K as KCl, and the subplot was cultivar (‘Mountain Spring’ or the high-lycopene Florida hybrid, ‘Fla. 8153’). The soil type was a well-drained, central Iowa loam with a soil test level considered low. The soil K application effect on total marketable fruit yield was linear ( P < 0.001, Y = 53 Mg·ha −1 + 0.084x, r 2 = 0.51) with both cultivars responding similarly. Fruit K analysis indicated a linear response to fertilization across four harvest dates, from 1236 to 1991 mg·kg −1 , fresh weight basis. Harvest date had no effect on fruit lycopene concentration, but there was a significant ( P = 0.006) interaction of K fertilization rate and cultivar. Overall, ‘Fla. 8153’ contained 9.5 mg·kg −1 more lycopene in fruit tissue than ‘Mountain Spring’. ‘Mountain Spring’ lycopene concentration was not enhanced by higher K fertilization (44.2 mg·kg −1 ). ‘Fla. 8153’ lycopene concentration increased 21.7% at the highest K rate compared with lower rates (62.9 vs. 51.7 mg·kg −1 , respectively). A controlled greenhouse study in the fall of 2005 with the same cultivars indicated similar results. Fruit K concentration for ‘Fla. 8153’ was significantly ( P < 0.01) correlated to the fruit carotenoids, phytoene and phytofluene, indicating a possible role for K in one of the enzymes that synthesize phytoene. In the field and greenhouse studies, increasing fruit K concentration in the high-lycopene ‘Fla. 8153’ depressed fruit β-carotene by 53%. These results indicate that K fertilization can affect carotenoid biosynthesis, and the response of tomato to a high K rate is genotype dependent.