Effect on temperature of lightweight plant cover enveloping papaya fruit (Carica papaya L.) in a naturally ventilated Mediterranean greenhouse

In recent years, the traditional horticultural crops in greenhouses on the Mediterranean coast as tomato have lost profitability. In this situation, a possible alternative is the production of tropical crops like Carica papaya. The plant growth in continental Europe presents the handicap of low winter temperatures. When air temperature falls below 12-14°C for several hours at night, papaya production can be affected. The objective of the present study was to analyze the effect of wrapping fruits with polypropylene lightweight non-woven curtain on the daily thermal oscillations and the production, in a naturally ventilated multispan greenhouse (1800 m²) in Almeria (Spain). White lightweight cover was placed around the fruit column, leaving the leaves out of the cover. The covers were used from December 11, 2017 to April 19, 2018 and placed around 30 trees in 111.11 m². Alternate rows with plant cover and without it were placed in the greenhouse. Temperature and humidity sensors were laid next to the unwrapped fruits at 1.5 m above the ground, in each row. At the same height, in plants with a plant cover, two sensors were placed close to the fruits, one inside the light white cover and one outside. As a result of the use of the plant cover, the minimum and mean temperature of the air inside of the thermal cover increased, respectively, 1 and 0.7°C. The augmentation of temperature seems to induce early production. The diurnal temperature range was reduced, and the reduction values were in the range of 0.4-1.2°C. No statistically significant increase in the yield (during the period using the plant cover) was observed in the wrapping plants, although production was 4.3 kg m^‑2 for protected plants and 3.5 kg m^‑2 without protection.