Effect of Temperature Regime and Soil Moisture Level on Fruit Quality of 'Summer Queen' Passionfruit (Passiflora edulis X P. edulis f.flavicarpa)

摘要

The high acidity of 'Summer Queen' passionfruit (Passiflora edulis x P. edulis f. flavicarpa) in the winter season lowers the taste and affects the acceptability to consumers. The present study was conducted to determine whether a high temperature regime and a high soil moisture level could improve the fruit quality by reducing the acidity in the winter season. Potted plants were grown in three different greenhouses where the maximum/minimum temperatures were 27.3/20.7 deg C (high), 25.3/19.4 deg C (medium), and 24.0/16.3 deg C (low) combined with three different soil moisture levels: high (around 18%), moderate (around 13%) and low (around 7%) by the application of irrigation at different intervals in a plastic house located at Ishigaki, Okinawa, Japan, to examine the fruit acidity at maturity in winter. The acid content was the highest under low temperature conditions combined with a low soil moisture level, and the lowest at a high temperature combined with a high soil moisture level. Since a high temperature accelerated fruit development, the peak of the acid content was observed at 50-55 days after pollination (DAP), while at 60-65 DAP under medium and low temperature regimes. Low soil moisture level delayed the peak of fruit acidity by 5 days irrespective of the temperature regimes. The number of days required to maturity were 60 to 75 DAP under high temperature conditions, 70 to 85 DAP under medium and low temperature conditions. Citric acid was the main organic acid in the juice of 'Summer Queen' passionfruit and the titratable acidity was correlated with the content of citric acid.