Posted with permission of J. Janick and the International Society for Horticultural Science
Avocado Fruit Development and Ripening Physiology
John P. Bower and Jonathan G. Cutting Citrus and Subtropical FruitResearch Institute, P/Bag X11208, Nelspruit 1200, South Africa
Introduction A. Environmental Aspects 231 B. Endogenous Controlling Systems
II. Avocado Fruit Development 230 233 238 239 243 244 246 248 252 259
III. Avocado Fruit Ripening A. Plant Growth Regulators B. Structural Changes C. Enzymes D. Calcium E. Modification of the Ripening Process F. Postharvest PhysiologicalDisorders IV. Conclusions
I. INTRODUCTION The avocado (Persea americana Mill.) has a long history as both a subsistence and marketable fruit in the areas of origin in Central and South America. Recently, however, a considerable trade has developed, both locally and internationally, with the fruit becoming well known in the industrialised areas of North America and Europe. The largest producers (Table7.1) are, nevertheless, not substantial exporters. Marketing remote from the production areas has become important to the avocado industries of the United States (particularly California and Florida), Israel, and South Africa. These three countries are the main exporters and account for 90% of the world's exports, with Israel having by far the largest percentage (Van Zyl and Groenewald 1986).Rapid expansion is also taking place in Spain, with much of the crop destined for Northern European markets. Trade with distant markets requires the production of high quality fruit and efficient transport so that it may arrive at the market in sound condition. There are, however, many references in the literature to mesocarp discoloration (Van Lelyveld and Bower 1984) and chilling injury (Chaplin etal. 1982) which Couey (1982) attributed to long periods of cold storage during the transport of avocado fruit.
Table 7.1. Annual Avocado Production in the Five Major Producing Areas of the World (Anon. 1986)
Country Mexico Brazil United States of America Dominican Republic Israel Production (million kg) 450 270 190 90 68
There have been a number of comprehensive reviews concerningfruit-ripening physiology in which avocados are invariably mentioned. This fruit is, however, an exception in that it does not follow the patterns of physiological changes associated with ripening in many other fruits (Rhodes 1981). An evaluation of ripening physiology of the avocado is, therefore, necessary in order to examine the possible cause of ripening and storage disorders. It would be insufficientto examine only postharvest factors affecting final fruit quality, as preharvest conditions pertaining to fruit growth and development also play a role (Bower and Van Lelyveld 1985; Bezuidenhout and Kuschke 1982; 1983). This review will therefore include avocado fruit growth and development, as a background to ripening physiology, transport, and long-term storage, with its associatedphysiological disorders. II. AVOCADO FRUIT DEVELOPMENT While numerous studies on avocado maturity have been made over the last 50 years (Barmore 1977), the physiological development of the avocado fruit has been largely neglected. The anatomical development of the avocado fruit has, however, been thoroughly investigated (Schroeder 1953). No attempt will be made to review flowering as this has been extensivelycovered by Davenport (1986). The growth of the avocado fruit follows the single sigmoid curve (Valmayor 1964; Robertson 1971). The early period of fruit growth, regardless of early or late maturing cultivars, is characterized by rapid cell division (Barmore 1977). Variations in fruit size of cultivars maturing at approximately the same time result primarily from differences in the rate of cell...