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Since psoralens have a very weak antifungal activity in vitro, we propose that (+)marmesin, the precursor of psoralens in celery (Apium graveolens L.) is associated with celery resistance to pathogens. (+)Marmesin has at least 100 times greater antifungal activity in vitro than psoralens. After 1 month of storage at 2C, the concentration of total psoralens increased from 8 to 67 μg·g-1 fresh weight, (+)marmesin decreased from 27 to 4 μg·g-1 fresh weight, and the incidence of decay increased from 0% to 34%. However, when celery was treated with GA3before 1 month of storage at 2C, decay increased to only 7%, the concentration of psoralens increased to 31 μg·g-1 fresh weight and the concentration of (+)marmesin decreased to 13 μg·g-1 fresh weight It seems that GA3 retarded celery decay during storage by slowing down the conversion of (+)marmesin to psoralens, thereby increasing the resistance to pathogens during storage.
Abstract
Yellowing and decay of leaves were reduced when romaine lettuce (Lactuca sativa L. cv. Hazera Yellow) was prepackaged in closed polyethylene (PE) bags in which O2 concentration was reduced by flushing with N2. Similar, but less effective results were obtained when the lettuce was prepackaged in closed PE bags (not flushed with N2 gas), or when open bags were placed in PE-lined cartons, as well as when lettuce was vacuum precooled after packaging in open bags. Vacuum precooling of PE-lined cartons of lettuce did not further delay deterioration, since the process of vacuum cooling eliminated the modified atmosphere previously produced in PE liners. The efficacy of PE-lined cartons and that of closed PE bags in delaying deterioration of lettuce was related to reduction of O2 and accumulation of CO2 in the ambient atmosphere in the package.
Concentrations of CO2 in PE-lined cartons, which reached 8 to 12% at the end of holding at 18 to 20°C following storage at 1°C, had no adverse effect on romaine lettuce. However, about 64% of the heads of ‘Great Lakes’ lettuce packed in similar packages during cold storage showed CO2 damage, even when CO2 was not higher than about 3%.
Abstract
A single preharvest spray of gibberellic acid (GA3), alone or with the cytokinin, isopentenyladenine (IPA), retarded leaf yellowing, and, to a lesser extent, leaf rot of romaine lettuce (Lactuca sativa L. ‘Hazera Yellow’). The most effective spray was 10 ppm GA3 plus 0.1 ppm IPA. Effects of 1 ppm GA3 together with 0.1 ppm IPA were similar to those of 25 ppm GA3 and were always superior to the controls (water-sprayed). Lettuce sprayed by the hormones and packed in polyethylene (PE) liners remained green and sound longer than that either sprayed or packaged.