“Cloud” or vascular browning in tomatoes

Summary The browning in the vicinity of the vascular system characteristic of cloud appears to be polyphenol oxidase browning. Polyphenol oxidase has been found to be active in abnormally ripening cloud‐affected wall tissue, but appears to be inactive in normally ripening wall tissue even in cloud‐affected fruit. High polyphenol oxidase activity has been found in very young fruits, diminishing and finally disappearing with increasing maturity. It is suggested that cloud‐affected fruits show an abnormal retention of polyphenol oxidase activity in the blotched areas. This activity persists in cloud tissue ripened to the orange‐red stage on the plant.