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The skin blackening of pear fruit (cv. Niitaka) was commonly induced when stored at low temperatures immediately after harvest. Some postharvest factors such as CO₂, ethylene, and relative humidity were examined to clarify their involvement with the disorder. Hunter L value decreased significantly in high CO₂ treatments (10 and 50%) than in relatively low CO₂ (1 and 3%) during storage of fruit. More ethylene was produced with high CO₂ supply from 1, 3, 10 to 50% while fruit supplied with external ethylene showed a non-climacteric behaviour due to low production of ethylene. One percent CO₂ treatment showed no skin blackening for 60 days storage, whereas this disorder appeared in same CO₂ concentration with ethylene supply in low RH at 38 days and in high RH at 46 days, respectively. Three percent CO₂ plus ethylene induced the skin blackening at 20 days of storage with existing ethylene while no skin disorder was found in same CO₂ concentration without ethylene. The disorder was accelerated significantly by higher CO₂ (10 and 50%), and continued to influence flesh color and flavor. Firmness, TA and vitamin C significantly decreased in both treatments of 10 and 50% due to high CO₂ injury. High carbon dioxide after appearing the skin blackening softened successively the flesh and consumed quickly the respiratory substrates. The flesh quality was little influenced by external ethylene supply and RH conditions. The skin blackening was influenced firstly by ambient CO₂ concentrations more than 1% and secondly by ethylene followed by high RH in ´Niitaka´ pear fruit.
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