Relationship between air temperature and degreening of lemon ('Citrus lemon' L. Burm. f.) peel color during maturation

Abstract

This study describes the relationship between air temperature and the loss of greenness in lemon peel and the appearance of the typical yellow color in the lemon varieties Eureka Frost, Lisbon Frost and the Fino 49, all on Citrus macrophylla rootstock. The change in the colorimetric coordinate a was studied, and the hue angle and chroma were calculated to ascertain the influence of temperature on these parameters. The study covered six campaigns (2003-2009), with measurements being made every week or fortnight in 10 fruit per tree and 4 trees per variety. The results show that the values of the colorimetric coordinate a (of the HunterLab) was most closely correlated with the mean of the minimum daily temperature of the 21 days prior to the measurement (adjusted R 2 >0.93). Identical results were obtained for Chroma and hue angle. It was determined that the color of the peel begins to change from green to yellow when the minimum temperature falls below 15 oC, reaching full “lemon yellow” below 6 oC. This means that in areas where the mean of the minimum temperatures of the 21 days prior to the measurement do not reach 15 oC, natural degreening will not occurr. As a consequence, artificial degreening, with the increased expense that this entails for the crop, will be necessary. The knowledge gained with this study will be of interest for determining the suitability of areas of the world where lemon tree plantations are being considered, so that prospective growers will not have to resort to artificial degreening.