Short anaerobiosis period prior to cold storage alleviates bitter pit and superficial scald in Granny Smith apples
BACKGROUND: Californian Granny Smith apples are very susceptible to bitter pit (BP) and superficial scald symptoms that developduring cold storage. The main preventive means are diphenylaminedipping and/or gaseous application of the ethylene inhibitor 1-methylcylclopropene (1-MCP),which is effective against superficial scald but not against BP. This study investigated the efficacy of a non-chemical alternative, low-O2 (LO2) stress, in preventing these two physiological disorders.
RESULTS: Application of LO2 stress at 20 °C for 10 days prior to cold storage of Granny Smith apples reduced superficial scald and BP incidence and severity during 8months at 0 °C. LO2 treatments induced volatile alcohols and reduced ethylene and 6-methyl-5-hepten-2-one (MHO-on) production, thereby reducing superficial scald development after 4 months at 0 °C. In addition, LO2-treated fruits had higher pectin methyl esterase (MdPME) gene expression, similar to that of 1-MCP-treated fruits, associated with their higher firmness. Conversion of MHO-on to 6-methyl-5-hepten-2-ol (MHO-ol) in LO2-treated fruits may explain the lower scald development.
CONCLUSION: The ratio between MHO-on and MHO-ol might serve as an index of superficial scald severity. Reduction of BP symptoms in LO2-treated fruits could be due to accumulation of volatile alcohols in the peel tissue.