Interactive Effects of Iron and Photoperiods on Tomato Plant Growth and Fruit Quality

Photoperiod and micronutrient iron (Fe) are critical for plant growth and development. However, the interactive effects of Fe nutrition and photoperiod on tomato plant growth and fruit quality remain elusive. In this study, the tomato genotype 'Micro-tom' was used to explore the influence of different concentrations of exogenous Fe (0, 100, 150, 200 μM Fe-EDTA) under two photoperiods (12 h/12 h and 16 h/8 h) on tomato plant growth, photosynthetic characteristics, and fruit quality parameters. The results show that compared with the 12 h/12 h photoperiod, the vegetative growth, and plant height decreased, but reproductive development (flowering and fruiting) improved under the 16 h/8 h photoperiod. Meanwhile, foliar spray with 100 or 150 μM Fe-EDTA improved the photosynthetic pigment content, the net photosynthetic rate, and the fruit quality indexes under both photoperiods. Moreover, the content of Fe increased, while the contents of K, Mg, and Mn, and the concentrations of individual and total amino acid decreased in tomato fruits. Under 16 h/8 h photoperiod, the contents of soluble protein, free amino acid, and lycopene significantly increased in tomato fruits by 90%, 84%, and 30%, respectively, after spraying the leaves with 100 μM Fe-EDTA. Similarly, the soluble solids, soluble sugar content, sugar-acid ratio, and vitamin C content in fruits increased by 71%, 171%, 246%, and 14%, respectively, after spraying with 150 μM Fe-EDTA. These results suggest that extending the illumination time to 16 h is beneficial to the development of tomato plants, and foliar application of 150 μM Fe-EDTA under 16 h/8 h photoperiod can best improve the flavor and nutritional quality of tomato fruits.