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Postharvest changes in flesh firmness, soluble solids concentration (SSC), and titratable acidity (TA) associated with increasing severity of sunburn browning of apples (Malus ×domestica Borkh.) were investigated over time in regular atmosphere cold storage. In 2005, ‘Gala’ apples were harvested at maturity and sorted into five classes ranging from no sunburn (Sb-0) to severe sunburn browning (Sb-4). Flesh firmness, SSC, and TA were measured on flesh tissue beneath the sunburned area of the apples at harvest and at monthly intervals for 6 months. In 2006, a similar protocol was used for ‘Gala’, ‘Golden Delicious’, ‘Jonagold’, ‘Granny Smith’, and ‘Fuji’ apples, except that these fruit quality traits were determined at harvest and after 3 and 6 months in regular atmosphere cold storage. Flesh firmness and SSC increased, but TA decreased both years in all cultivars as sunburn severity increased from Sb-1 to Sb-4. The patterns of higher firmness with more severe sunburn browning persisted during cold storage even though firmness in all classes of fruit decreased gradually with time in cold storage. The patterns of lower TA as severity of sunburn increased also persisted during cold storage, but TA declined more markedly in apples with more severe sunburn. The ratio of SSC to TA (SAR) increased as the severity of sunburn increased in all five cultivars. The SAR also increased dramatically from harvest to 3 and 6 months after harvest with ratios exceeding 200 in Sb-4 of some cultivars after 6 months storage. This occurred because TA declined very markedly as time in cold storage increased. Relative water concentration of tissue in sunburned areas of apples declined as the severity of sunburn increased, and helps to account for the higher SSC and firmness observed in sunburned apples.
Gibberellins inhibit flowering in apple (Malus domestica) and show promise as tools to promote annual bearing. The authors validated the efficacy of gibberellic acid (GA) to reduce return bloom dramatically in two biennial cultivars. ‘Honeycrisp’ fruit treated in 2004 with GA4+7 at 0, 200, 400, or 600 mg·L−1 demonstrated advanced maturity in terms of starch levels, flesh firmness, and titratable acidity, whereas ‘Cameo’ fruit showed variable treatment effects. In 2005, 0, 300, 600, 900, or 1200 mg·L−1 GA4+7 was applied to ‘Cameo’, and fruit maturity was once again unaffected. Two commercial GA products (GA4, GA4+7) were applied in 2005 to ‘Honeycrisp’ at 400 mg·L−1. Both formulations caused fruit to have less flesh firmness and acidity, and increased levels of starch conversion compared with the untreated control at harvest and after 140 d of common storage. All GA treatments in all four trials profoundly diminished flowering in the season after treatment. Results demonstrate differences in sensitivity to GA between the two cultivars.