Effects of Short-Term Root Cooling before Harvest on Yield and Food Quality of Chinese Broccoli (Brassica oleracea var. Alboglabra Bailey)

Vegetable product quality is an important consideration for consumers. Long-term root cooling could improve certain food quality of horticultural crops, but often comes at the expense of reduced shoot biomass or yield. Since few studies have investigated how fast Chinese broccoli (Brassica oleracea var. alboglabra Bailey) responds to changes of root temperature, we shortened the duration of the root cooling treatment to one week before harvest to make the production system more effective. The aim of this study was to improve the food quality of Chinese broccoli without causing deleterious effects on plant growth and yield. The seedlings were cultivated hydroponically at two root temperatures (10 and 20 °C) during the last week prior to harvest in summer 2018 (Exp-1) and autumn 2019 (Exp-2). Plant growth, yield, physiological variables, soluble sugars, total chlorophyll, glucosinolates and mineral elements concentration were examined. The results showed that the yield reduction was alleviated compared to results over the long-term. Specifically, yield was not affected by root cooling in Exp-1 and reduced by 18.9% in Exp-2 compared to 20 °C. Glucose and fructose concentrations of the leaves were increased when the root temperature was 10 °C in both experiments with a more pronounced impact in Exp-2. In addition, root cooling produced a significant accumulation of individual glucosinolates, such as progoitrin, gluconapin, 4-methoxyglucobrassicin and 4-hydroxyglucobrassicin, in the stems of Exp-1 and the leaves of Exp-2. Minerals, such as N, showed reductions in the shoot, but accumulation in the root. Therefore, compared to long-term root cooling, short-term (one week) reduction of the root temperature is more economical and could help improve certain quality characteristics of Chinese broccoli with less or even no yield reduction.

Effects of Root Temperature on the Plant Growth and Food Quality of Chinese Broccoli (Brassica oleracea var. alboglabra Bailey)

Root temperature has long been considered an essential environmental factor influencing the plant’s physiology. However, little is known about the effect of root temperature on the quality of the food produced by the plant, especially that of horticultural crops. To fill this gap, two independent root cooling experiments (15 °C vs. 20 °C and 10 °C vs. 20 °C) were conducted in autumn 2017 and spring 2018 in hydroponics with Chinese broccoli (Brassica oleracea var. alboglabra Bailey) under greenhouse conditions. The aim was to investigate the effect of root temperature on plant growth (biomass, height, yield) and food quality (soluble sugars, total chlorophyll, starch, minerals, glucosinolates). A negative impact on shoot growth parameters (yield, shoot biomass) was detected by lowering the root temperature to 10 °C. Chinese broccoli showed no response to 15 °C root temperature, except for an increase in root biomass. Low root temperature was in general associated with a higher concentration of soluble sugars and total chlorophyll, but lower mineral levels in stems and leaves. Ten individual glucosinolates were identified in the stems and leaves, including six aliphatic and four indolic glucosinolates. Increased levels of neoglucobrassicin in leaves tracked root cooling more closely in both experiments. Reduction of root temperature by cooling could be a potential method to improve certain quality characters of Chinese broccoli, including sugar and glucosinolate levels, although at the expense of shoot biomass.

The Effects of Root Temperature on Growth, Physiology, and Accumulation of Bioactive Compounds of Agastache rugosa

Plants respond to root temperature stresses by producing antioxidants as a defense mechanism. Since a number of these are phytochemicals with enhancing effects on human health, we examined the effects of 4 root-zone temperature (RZT) treatments (10, 20, 28, and 36 °C) on plant growth and the main bioactive compound concentrations in each organ of Agastache rugosa plants. We aimed to determine the optimal RZT treatment to increase bioactive compound concentrations with no deleterious effects on plant growth. Four-week-old seedlings were grown in a plant factory for 32 days. Nine plant growth parameters, namely, shoot and root fresh weights, stem and root lengths, leaf length and leaf width, leaf area, and shoot and root dry weights were significantly decreased at 10 and 36 °C compared with other treatments. A similar pattern was observed for the chlorophyll content and leaf gas exchange parameters. Of all the RZT treatments, RZT at 28 °C produced the significantly greatest accumulation of two major bioactive compounds, namely, rosmarinic acid (RA) and tilianin contents per the A. rugosa plant, and had no adverse effects on the overall growth of A. rugosa. This supports the use of 28 °C RZT to successfully improve the bioactive compounds with no adverse influence on plant growth or yield.

Effects of Root Cooling on Plant Growth and Fruit Quality of Cocktail Tomato during Two Consecutive Seasons

Understanding the effects of root temperature on plant growth and key food components of horticultural crops under greenhouse conditions is important. Here, we assess the impact of root cooling on plant growth and fruit quality of two cocktail tomato cultivars (Lycopersicon esculentum cv “Amoroso” and cv “Delioso”) during the winter of 2017-2018 and the summer of 2018. Plants were grown hydroponically on rockwool under different root temperatures (16–27°C and 10°C) from the 2nd inflorescence to harvest inside the greenhouse. A root temperature of 10°C was controlled independently from air temperature (18–23°C in winter and 21–29°C in summer) by circulating cooling water. Reductions of marketable yield per plant (7.9–20.9%) in both cultivars were observed in response to root cooling in winter, but not significantly in summer. In most cases, root cooling had a positive effect on the functional quality (sugars, vitamin C, and carotenoids levels). In the case of “Delioso,” glucose concentration increased by 7.7–10.3%, vitamin C by 20–21%, and lycopene by 16.9–20.5% in both seasons. “Amoroso” exhibited only higher consistent values in glucose with increments between 6.9 and 7.8% in the two seasons. The levels of elements decreased by root cooling, with statistically significant reduction of N, P, S, and Fe by 12.1–15.7% in “Delioso” in winter and P and Zn by 9.1–22.2% in both cultivars in summer. Thus, manipulation of root temperature could be a feasible method to improve the overall fruit quality of cocktail tomato; however, this effect was also dependent on cultivars and other environmental factors.

Electrical and Thermal Transport Properties of Layered Superconducting Ca10(Pt4As8)((Fe0.86Pt0.14)2As2)5 Single Crystal

We have synthesized single crystals of iron-based superconducting Ca10(Pt4As8)((Fe0.86Pt0.14)2As2)5 and performed extensive measurements on their transport properties. A remarkable difference in the behavior and a large anisotropy between in-plane and out-of-plane resistivity was observed. Disorder could explain the in-plane square-root temperature dependence resistivity, and interlayer incoherent scattering may contribute to the out-of-plane transport property. Along the ab plane, the estimated value of the coherence length is 15.5 Å. From measurements of the upper critical magnetic field Hc2 (T ≥ 20 K), we estimate Hc2(0) = 313 T. Thermal conductivity for Ca10(Pt4As8)((Fe0.86Pt0.14)2As2)5 is relatively small, which can be accounted for by the disorder in the crystal and the low-charge carrier density as verified by the Hall effect.

Influence of Beet necrotic yellow vein virus and Freezing Temperatures on Sugar Beet Roots in Storage

Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) is a yield-limiting sugar beet disease that was observed to influence root resistance to freezing in storage. Thus, studies were conducted to gain a better understanding of the influence of BNYVV and freezing on sugar beet roots to improve pile management decisions. Roots from five commercial sugar beet cultivars (one susceptible and four resistant to BNYVV) were produced in fields under high and trace levels of rhizomania pressure and subjected to storage using five temperature regimes ranging from 0 to −4.4°C for 24 h. After cold treatment, eight-root samples were stored in a commercial indoor storage building (set point 1.1°C) for 50 days in 2014 and 57 days in 2015. Internal root temperature, frozen and discolored tissue, and moisture and sucrose loss were evaluated. The air temperature at 0, −1.1, and −2.2°C matched internal root temperature but internal root remained near −2.2°C when air temperature was dropped to −3.3 and −4.4°C. In a susceptible cultivar produced under high rhizomania pressure, the percentage of frozen tissue increased (P < 0.0001) from an average of 0 to 7% at 0, −1.1, and −2.2°C up to 16 to 63% at −3.3°C and 63 to 90% at −4.4°C, depending on year. Roots from the susceptible cultivar produced under low rhizomania pressure and those from the resistant cultivars from both fields only had elevated (P ≤ 0.05) frozen tissue at −4.4°C in 15 of 18 cultivar–year combinations. Frozen tissue was related to discolored tissue (r2 = 0.91), weight loss (r2 = 0.12 to 0.28), and sucrose reduction (r2 = 0.69 to 0.74). Consequently, BNYVV will not only lead to yield and sucrose loss in susceptible sugar beet cultivars but also to more frozen root tissue as temperatures drop below −2.2°C. Based on these observations, the air used to cool roots in nonfrozen sugar beet piles throughout the winter should not drop below −2.2°C to maximize sucrose retention.