Physiological responses of tomato fruit to ethylene at high temperature /

Abstract

Lycopene biosynthesis during ripening is inhibited at temperatures of 30C or higher. Tomatoes are typically harvested at a mature but unripe stage of development ("mature green") and treated with C 2 H 4 to initiate ripening. Tomato pulp temperatures may be 30C or greater during parts of the harvest season in Florida and other production areas. In this study, the response of tomatoes to C 2 H 4 at temperatures of 30C and greater was investigated in terms of color development, respiration, C 2 H 4 production, suberization and infection by G. candidum. Tomatoes held in air at 20 to 35C for 24, 48 or 72 hr, then transferred to 20C, ripened slowly and nonuniformily compared to fruit previously treated with C 2 H 4 at the same temperatures and for the same periods of time. Prior exposure to 100 ppm C 2 H 4 at 30C and, in some instances, 35C stimulated red color development in air at 20C. When the duration of C 2 H 4 treatment at 40C was increased to 48 or 72 hr, subsequent red color development was inhibited after transfer to air at 20C. Further vii increase in C 2 H 4 treatment concentration to 1 ,000 ppm did not alter the fruit response to high temperature. There were few ripening behavior differences in terms of respiration, C 2 H 4 production and 1-amino-cyclopropane-carboxylic acid oxidase activity in air at 20C in tomatoes previously exposed to C 2 H 4 at high temperatures (> 30C) for 24 hr compared to those treated at lower temperatures (i.e. 20 and 25C). Ethylene production was inhibited after 48 or 72 hr at 40C but lower temperature exposure stimulated C 2 H 4 production in the following order: 35 > 30 > 25C. During ripening in air at 20C, ACC conversion to C 2 H 4 increased in fruit previously exposed to C 2 H 4 at 20 or 25C but did not change in fruit from 30 or 35C, while exposure to 40C resulted in the lowest ACO acitivity. Fruit previously treated with C 2 H 4 for 72 hr at 30C lost less weight than fruit held at 30C for 24 hr or 48 hr, which lost as much weight as fruit held at 20 or 25C. Fruit held at 35C lost the most weight. There was enough evidence to conclude that the optimum conditions for suberization are between 25 and 30C and near saturation humidity. Wounded mature green tomatoes were inoculated with Geotrichum candidum, placed at 20, 25, 30, 35 or 40C, and treated with air or C 2 H 4 and near saturation RH. Wounded tomatoes previously treated with C 2 H 4 at 35, 30 or 25C subsequently exhibited increased disease development after 9, 10, or 1 1 days in air at 20C, respectively, compared to fruit previously treated with air only. 'Sour rot' severity in air at 20C after at least 9 days increased as the temperature of previous exposure while treating with air or C 2 H 4 increased from 20 to 25 and 30C and then declined in fruit that came from 35C. A thermophilic bacteria, which caused decay only in wounded tomatoes at temperatures > 35C, was identified as probably being a Bacillus species after Gram testing. viii

Management of Postharvest Diseases of Vegetables in a Tropical and Sub-tropical Environment of the Kingdom of Eswatini

“…Senescing vegetables are more susceptible to opportunistic postharvest pathogens. Manipulation of C 2 H 4 technologies in order to suppress its production, perception, signal transduction and action will reduce the rate of senescence of vegetables [39,40] and subsequently reduce relative susceptibility to pathogen attack. Suppression of gene expression through anti-sense technologies of cell wall degrading enzymes: pectin methyl esterase (PME) and polygalacturonase (PG) will help keep cell walls of vegetables intact [36,37,38,39].…”