Ethylene Evolution Stimulated by Chilling in Citrus and Persea Sp

Chilling temperatures (below 10' but above the freezing point of the tissue) injure fruits of coldsensitive crops native to tropical and subtropical areas (1,4, 5). Sweet orange (Citrus sinensis Osb.) fruits, even though mature internally, may not lose their chlorophyll on the trees when grown in tropical climates. However, oranges grown on the northern fringes of the sutbtropical regions of Florida, Texas, Arizona, and California lose their green color at the onset of cool autumtnn weather (4). Yellowing and shedding of leaves occur in the trifoliate orange [Poncirus trifoliata (L.) Raf.] in subtropical and temperate regions (6). Most citrus varieties, however, are evergreen, in the sense that the leaves normally remain green allI fall and winter. The physiological reasons for these chilling-induced phenomena are not known. Cooper et al. (3) reported that chilling temperatures of 5' increased the evoluttion of ethylene in calamondins (C. reticulata -var. anstera? X Fortunella sp?) ; and thereafter, the fruit lost its chlorophyll con-tent rapidly. We now have gas chromatographic evidence that chilling causes ethylene production in fruit of grapefruit (C. paradisa Macf.), sweet oranges, and avocados (Persea avierican,a Miller), and in leaves of the deciduotus trifoliate orange before leaf abscission.