Applications of magnesium affect pericarp colour in the Feizixiao lychee

Abstract

The pericarp of the Feizixiao lychee (Lychee chinensis Sonn.) remains green when the concentration of sugar in the aril peaks, the so-called stay-green phenomenon. The objective of the present study was to evaluate the effect of foliar-applied Mg on pericarp colour, and to determine the relationship between pericarp colour, plant growth substances, and activities of the key enzymes associated with colour development. We quantified the pigment concentrations and endogenous plant growth substances (abscisic acid–ABA–and ethylene), and determined the activities of chlorophyllase (Chlase), pheophorbide acid monooxygenase (PaO), and UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT). Magnesium was found to increase the accumulation of anthocyanin in the pericarp, and contributed to the red colour of the pericarp and overcame the stay-green phenomenon. In contrast, Mg had no effect on the concentration of chlorophyll in the pericarp. Strong relationships between anthocyanin, UFGT, and ABA suggest that the enzyme increased the accumulation of anthocyanin by increasing the concentration of ABA and the activity of UFGT. Strong negative relationships between chlorophyll, PaO and Chlase, and ethylene production suggest that ethylene increased the degradation of chlorophyll by increasing the activity of the two enzymes. The Mg spray was suggested for application in lychee orchards.