While most of lemon cultivars in the northern hemisphere are harvested 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 evolution 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 was studied, and then the influence of the minimum temperatures on the change from green to yellow, using the data collected over five growing seasons, was also assessed. The results confirmed the relation between net solar radiation and degreening in Verna, 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 is8.8 ºC or when the daily mean temperature reaches5.5 ºC on two consecutive days. The information 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.
