Higher quality and nutritional value in cherry tomatoes with Ultrasol®ine K Plus

The application of Ultrasol®ine K Plus resulted in more uniform bunches, better fruit weight, higher antioxidant levels and more calcium in the fruit of cherry tomatoes at a research station.

Iodine (I) should be considered as a plant nutrient. This is the main conclusion of Kiferle et al., 2021. In that work they published the presence and identity of natural iodinated proteins in higher plants, which had never been described before. Eighty-two iodinated proteins have been identified that are involved in important biological processes in higher plants. Like deficiency of any other plant nutrient, iodine deficiency can lead to yield losses.

In fertigation and protected horticultural crops grown in a commercial production environment, iodine deficiency can occur when the presence of iodine in the nutrient solution is below a target value of sufficiency. In intensive and fertigation under cover cropping systems, the nutrient solution and irrigation water are the main sources of iodine. This deficiency will manifest itself in the form of suboptimal root or leaf development, delayed flowering, reduced fruit growth and reduced stress resistance, resulting in lower yields compared to a crop that has been supplied with sufficient iodine in the nutrient solution.

At a research station in Almeria, Spain, cherry tomatoes of the variety "Genio" were grown in a sandy soil, following local commercial practice. The research station monitored fertilizer application, crop data recording, and water and plant tissue sampling.

In one sector (300^m2) a fertigation rate of potassium nitrate without iodine (control) was compared with the other sector (300^m2) in which Ultrasol®ine K Plus (potassium nitrate containing a fixed amount of iodine) was applied as a source of K and N - and iodine - in the nutrient solution. Both potassium nitrate sources were applied at the same dose and at the same time in a nutrient solution following local recommendations (Table 1). Ultrasol®ine K Plus was applied throughout the growing season (August-February), starting at transplanting.

Prior to the trial, irrigation water samples were taken and the iodine concentration in these samples was measured. The iodine concentration in both the irrigation water and the soluble fraction of the soil (1:2 water extract), was less than μmol ^L-1. The amount of iodine in Ultrasol®ine K Plus was aimed at correcting the iodine concentration between 1 and 10 μmol ^L-1 in the root zone. For each sector, fruit weight was recorded on 5 occasions during cultivation. In addition, to see the effect of iodine on fruit quality, fruit concentration of phenolic compounds and vitamin C was determined on one sampling date, and fruit calcium concentration was measured in samples taken on 5 different dates. On these same dates, iodine concentration was also determined in the first fully developed leaf of the plants from which fruit samples were taken.

The application of Ultrasol®ine K Plus produced a five-fold increase in iodine in the leaves of tomato plants. In the sector where Ultrasol®ine K Plus was applied, fruit weight was higher, and these fruits contained more antioxidants and calcium, compared to the control sector (Table 2).

Calcium concentration in fruit was particularly high in the months of December-February (Figure 1). In December, fruit bunch quality (vine cherry tomato) was observed to be deteriorated in the untreated (iodine-deficient) control compared to the Ultrasol®ine K Plus sector. The lower fruit quality in the control sector was related to cloudy weather during fruit development in the period prior to observation (Figure 2). In contrast, good fruit and bunch quality was observed in the Ultrasol®ine K Plus sector during the same period. The positive response in fruit quality to the application of Ultrasol®ine K Plus can be interpreted as a correction of a suboptimal level of iodine in the irrigation water. With a sufficient level of this micronutrient in the root zone, plants can iodize proteins in roots and leaves. These proteins have important functions in biological processes involved in growth, stress signaling and antioxidant production in roots and leaves. This allows the plant to maintain optimal levels of photosynthesis and sugar metabolism, even in the face of environmental stress.

Table 1. Macronutrients supplied with fertilizers in the nutrient solution applied at each irrigation.

*Irrigation water contained ^thefollowing elements (in mmol ^L-1) Ca 2.7; Mg 2.8; _SO4 0.5; Na 6.1; Cl 12.8

Table 2. Treatment means ± standard deviation of fruit weight and antioxidants in fruits of harvested cherry tomatoes in the sectors where the application of potassium nitrate without iodine in the control (Control) was compared with the application of potassium nitrate with iodine(Ultrasol®ine K Plus). Mean fruit calcium concentration is based on the average of 5 monthly analyses* statistically significant LSD, p<0.05.

Calcium concentration in cherry tomato fruits harvested in sectors with potassium nitrate without iodine (Control) or with Ultrasol®ine K Plus in the nutrient solution at each sampling time.

A pronounced difference in bunch quality was observed after a period of darkness and cold weather, with more uniform and better colored bunches in the Ultrasol®ine K Plus sector compared to the control.

The original publication is available at: https://doi.org/10.17660/ActaHortic.2021.1321.27