Influence of High Tunnel Microclimate on Fruit Quality and Calcium Concentration in ‘Santina’ Sweet Cherries in a Mediterranean Climate

Abstract

The use of protective covers, such as high tunnels, is recognized as an effective technology to reduce rain-induced fruit cracking in sweet cherries; however, there is a lack of information concerning the effects of this production system on the fruit’s mineral concentration, quality, and postharvest life. This study assesses the feasibility of using high tunnels on ‘Santina’ sweet cherries under the Mediterranean climate of the Central Valley of Chile to obtain earlier harvests of high-quality fruit with long storage life. The study included two plots: Plot 1 during the 2018/2019 growing season, and Plot 2 during the 2019/2020 growing season. High temperatures and relative humidity inside the high tunnels during bloom and fruit set decreased fruit yield, particularly in Plot 1. On average, trees inside the high tunnels were harvested 11 days earlier than those in the open. Fruit from covered trees were significantly larger (13%) and softer (10%) than those from the outside. Fruit quality characteristics, such as soluble solids concentration and titratable acidity, were not affected by high-tunnel-protected cultivation. Fruit from covered and uncovered trees maintained the firmness differences obtained at harvest between treatments, but showed similar postharvest quality after 45 days at 0 °C and a further 3 days at 20 °C on the other characteristics. The covered fruit had lower Ca concentrations (7.7 mg 100 g−1) and higher K:Ca, Mg:Ca, and N:Ca ratios. Significant relationships were found between Ca or K:Ca and fruit firmness at harvest. Lower Ca concentrations in the fruit may explain the lower firmness of fruit grown under plastic covers. There were no differences between covered and uncovered cherries in either cracking susceptibility or induced pitting. ‘Santina’ cherries were very sensitive to pitting damage, but this is not associated with the fruit’s Ca concentration. The results obtained show that high tunnels influenced fruit yield, development, and quality, and emphasize that the fruit’s Ca concentration under this growing condition plays a significant role in the firmness of ‘Santina’ sweet cherries.

Impact of Potassium Pre-Harvest Applications on Fruit Quality and Condition of Sweet Cherry (Prunus avium L.) Cultivated under Plastic Covers in Southern Chile Orchards

“…In this work, in order to assess the impact of light exposure on fruit quality, fruits of the upper and lower area of the canopy were evaluated separately. As a result, we detected firmer fruits in the lower area of the canopy, independent of the treatments, which had already been observed in previous studies in a temperate climate [21,25]; this could be in response to a delay in the maturation of fruits located in the lower area of the canopy, which is highly shaded by the upper area. Reduced sweet cherry fruit firmness by the use of plastic covers detected here, which has also been previously reported [18,21,22], could be explained by the lower levels of calcium (Ca) detected in fruits grown under plastic covers [25].…”

“…Nonetheless, the cultivation of sweet cherry in the southern zone (temperate rainy climate) is frequently affected by several climatic constraints, including the high incidence of rains at bloom and pre-harvest, which forces producers to use plastic covers to mitigate flower falls and, most importantly, fruit cracking. The impact of the use of plastic covers on sweet cherry has been poorly explored; however, some studies have shown that its use can increase the caliber and reduce the cracking [41,42] of fruits but decrease cherry firmness [18,21,22,25] and soluble solids contents [43,44]. On the other hand, according to information provided by the fruit export company Ranco Cherries of Chile, the cherry produced in southern Chile exhibits low acidity levels, which worsens with the use of covers, a factor that is stronger in more southern regions.…”

“…The protective covering installed at flower bud-burst increased fruit size, weight, and soluble solids content but reduced fruit firmness. Similarly, Blanco et al [25] studied the feasibility of using high tunnels on 'Santina' sweet cherries under the Mediterranean climate of the Central Valley of Chile to obtain earlier harvests of high-quality fruits with long storage life. They found that high temperatures and relative humidity inside the high tunnels (during bloom and fruit set) decreased fruit yield and that trees inside the high tunnels were harvested 11 days earlier.…”

“…Besides representing a physical barrier that prevents direct water contact with the fruit surface, plastic covers can modify the micro-environmental conditions of the orchards, increasing both air temperature (by almost 15 • C) and relative humidity [21,22], thus protecting fruit crops against frost but increasing the incidence of fungal diseases [23]. Previous works have shown that plastic covers can negatively alter fruit quality parameters such as firmness (decreases) and caliber (increases) [21,24,25], decreasing the resistance of fruits to mechanical damage that can occur during harvest, handling, and a long postharvest trip. In addition, a notorious decrease in the crispiness sensation, an attribute desired by consumers, has been lately reported [25,26].…”

“…Previous works have shown that plastic covers can negatively alter fruit quality parameters such as firmness (decreases) and caliber (increases) [21,24,25], decreasing the resistance of fruits to mechanical damage that can occur during harvest, handling, and a long postharvest trip. In addition, a notorious decrease in the crispiness sensation, an attribute desired by consumers, has been lately reported [25,26]. Moreover, deficient skin color and low acidity levels have been detected in sweet cherries produced in several southern Chile locations, probably explained by reduced radiation under plastic covers and the low thermal sum of this zone [27].…”