Initial low oxygen stress controls superficial scald of apples

Abstract

The effectiveness of initial low oxygen stress (ILOS) to control apple scald without postharvest application of scald inhibitors and fungicides was investigated. Scald susceptible (‘Granny Smith’, ‘Law Rome’, ‘Red Delicious’) and not susceptible (‘Idared’) fruits were harvested preclimacterically and treated at 1°C with (1) ILOS pretreatment or (2) no pretreatment as control. Fruit were then stored at 0.5–1°C in 3% O 2 with 0% CO 2 , 1.5% O 2 with 3% CO 2 , or 0.7–0.8% O 2 with 3% CO 2 in flow-through controlled atmosphere (CA) or in air. ILOS of 0.5 and 0.25% O 2 for 2 weeks resulted in excellent control of scald when fruits were subsequently held in CA (3% O 2 , 0% CO 2 ). Initial treatment with 0.25% O 2 for 2 weeks, and when this treatment was supplemented with an additional 2 weeks of low O 2 stress after 2 months of storage, were more effective treatment regimens for scald control than all other treatments. ILOS followed by CA storage at 1.5% O 2 gave complete control of scald. A commercial test of initial low O 2 stress confirmed its efficacy for controlling scald in several cultivars of apples. The production of α-farnesene and its volatile oxidation product 6-methyl-5-hepten-2-one (MHO) was inhibited by initial low O 2 stress treatments and 1.5% O 2 CA. The 0.25% O 2 initial stress treatment caused stronger inhibition of α-farnesene and MHO production than 0.5% O 2 initial stress treatment. The accumulation of MHO was related to scald development of apples.