To identify the stage of flower development sensitive to low temperature-induced rough blossom-end scarring (RBS) in tomato (Lycopersicon esculentum Mill.), short-term low-temperature treatments (1, 3, and 5 days continuously at 10C or 6, 9, and 12 days at 18/10C day/night) were applied to young, flowering plants and to plants at the six-leaf stage. Flowers were tagged at anthesis over 4 weeks and the growth stage of the flowers at the beginning of the treatments was determined in days relative to anthesis. The blossom-end scar index (BSI), a measure for blossom-end scar size relative to fruit size, and number of locules were recorded for mature fruits. In three experiments, 5 days at 10C or 6 days at 18/10C, applied during early flower differentiation, induced RBS in mature fruits. For each of the three cultivars tested `Horizon', Waker', and `Solar Set'), flower buds were most sensitive from 26 to 19 days before anthesis. In this experiment, RBS induction was not caused by an increase in the average number of locules per fruit. A short period of sensitivity during very early flower development explains the variation in RBS among seasons and within plants encountered in field situations. This study also presents a standard induction technique for further investigation of physiological and morphological backgrounds of the disorder and possible genotype screening.
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