RELATION BETWEEN TEMPERATURE AND THE COLOUR COORDINATE

This study analyze the influence of temperature on the evolution of the colour coordinate ‘a’ in the peel of the lemon cultivars ‘Eureka Frost’, ‘Lisbon Frost’ and the clone ‘Fino 49’, all on Citrus macrophylla rootstock. The study covered six seasons (2003/04 and 2005/06 to 2009/10) with measurements made every week or fortnight. The results point to greater correlation between the colour coordinate ‘a’ in peel and low temperatures than medium temperatures. The correlation between the colour coordinate and low temperatures is the greatest for the mean value recorded during the previous 21 days. The correlation for the loss of greenness in lemon peel increases when the average of the minimum temperatures, rather than the average of the means, is considered. The negative values of the colour coordinate ‘a’ decrease below 15-17°C, increasing as the minimum temperatures fall until they reach zero. The colour coordinate ‘a’ and the average minimum temperature for the 21 days preceding the measurement provide excellent adjustments. The good values of R² for the cultivars ‘Eureka’, ‘Fino’ and ‘Lisbon’ show that the synthesis of the many carotenoids in the peel varies as a function of temperature. The model presents a higher correlation considering the variable ‘a’ for a period and for the previous observation. For this purpose we use a fixed type model.