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Abstract
The disorder known as Jonathan spot commonly observed on ‘Jonathan’ apples actually consists of 2 spot types which must be distinguished in order to define the affecting factors and to resolve the confusing and contradictory evidence in the literature. The spots which occur in the epidermal tissues without definite relation to lenticels are considered as Jonathan spot. Those which occur directly around the lenticels are defined as lenticel spots.
Histologically, the epidermal tissues afflicted with Jonathan spot showed a significant radial compression of the collenchyma cells in the 4 to 7 subepidermal tiers; whereas, such modification was not always apparent in tissues affected with lenticel spot. For the latter, some degree of rupture of the epidermis and the 3 to 5 subepidermal collenchyma tiers was usually noted. Jonathan spot development was inhibited by high temperature (70°F). It was favored by delayed harvest, yet none was observed until the fruit was stored at low temperature for several months. Conversely, lenticel spot often was present at harvest time and its development was accelerated at high temperature and inhibited at low temperature. High relative humidity (90%) enhanced lenticel spot development, whereas, humidity level had no effect on Jonathan spot.
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.