Quality and fruit colour change in Verna lemon

Abstract

While most lemon cultivars in the northern hemisphere are harves¬ted in autumn-winter, Verna, an autochthonous Spanish cultivar, is harvested later (February to August), supplying the European market when lemons are in short supply, a market that is also served by imports from the southern hemisphere, mainly Argentina and South Africa. The aim of this study was to determine the temperature at which degreening begins naturally in Verna lemon, noting the evo¬lution of colorimetric parameter a and comparing the same with the equivalent measurements made in Eureka lemon, the most widely cultivated lemon worldwide. The influence of solar radiation on the colorimetric parameters in Verna was studied, and the influence of the minimum temperatures on the change from green to yellow, using the data collected over five growing seasons, was assessed. The results confirmed the relation between net solar radiation and degreening, a process that begins when net solar radiation reaches a value of between 2 and 4 MJ/m2.day and when the mean temperature of the 14 days prior to sampling is 8.8 °C or when the daily mean temperature reaches 5.5 °C on two consecutive days. The informa¬tion obtained will enable growers to predict the colour changes that will occur in the field and potential growers to ascertain whether a given geographical zone is suitable for the crop in question.