VARIATIONS IN CHILLING INJURY AND EPICUTICULAR WAX COMPOSITION OF WHITE GRAPEFRUIT WITH CANOPY POSITION AND FRUIT-DEVELOPMENT DURING THE SEASON

'White grapefruit from interior and exterior tree canopy positions wer e harvested monthly over an 8-month season, and their epicuticular wax composition and susceptibility to chilling injury during cold storage were determined. Chilling injury was quite pronounced during the enti re season in exterior canopy and to a far less degree in interior cano py fruit when stored at 5 degrees C. Fruit from both canopy positions stored at 15 degrees C were free of chilling injury. Levels of wax, as measured by gas chromatography, increased throughout the season but a t a more rapid rate and to higher levels in exterior canopy fruit. Lev els of total wax increased greatly in fruit from both canopies when th e fruit were stored at 15 degrees C, indicating that, in grapefruit, c hilling injury is not directly related to the level of total epicuticu lar wax. The seasonal and 15 degrees C stored fruit increases were mos t pronounced in the aldehyde, alkane, and linear alcohol wax fractions and less in the triterpene fraction. Chromatograms of the exterior an d interior canopy fruit triterpene fractions were quite different, ind icating possible relationships of triterpenes, sun exposure, and chill ing injury. The sun-exposed and shaded sides of exterior canopy grapef ruit were assayed for chilling injury development and relative percent ages of components in the triterpene fraction of the wax. Four major t riterpenols were greater on sun-exposed surfaces compared with shaded surfaces, while six triterpenones showed the reverse trend. Ratios of the 10 triterpenes in exterior versus interior canopy grapefruit mirro red the respective ratios of 10 triterpenes in sun-exposed and shaded sides of the fruit, indicating that triterpenes may interact with sunl ight and possibly alter the susceptibility of grapefruit to chilling i njury.