Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: 3/31/2004
Publication Date: 6/24/2004
Citation: Pechous, S.W., Whitaker, B.D., Watkins, C.B. Expression of alph-farnesene gene afsi in relation to levels of faresene and conjugated trienols in peel tissue of scald-susceptible 'law rome' and scald-resistent 'idared' apple fruit. Hortscience. 2004. 39(4):782.
Technical Abstract: Fruit of different apple cultivars vary widely in their susceptibility to the storage disorder superficial scald. The genetic and biochemical factors involved in this variation are unknown. Conjugated trienol (CTol) oxidation products of the sesquiterpene alpha-farnesene are thought to play a major role in the induction of scald, and a high rate of farnesene accumulation in peel tissue of scald-susceptible apples early in storage is often associated with later development of the disorder. Pre-storage treatment of apple fruit with 1-methylcyclopropene (1-MCP) strongly inhibits the early burst of farnesene production and prevents scald, suggesting that ethylene induces transcription of key genes involved in farnesene biosynthesis. We recently cloned a gene from apple peel tissue, AFS1, which encodes alpha-farnesene synthase, the final, rate-limiting enzyme in the farnesene biosynthetic pathway. In this study, expression of AFS1 was compared in scald-susceptible 'Law Rome' and scald-resistant 'Idared' apples at harvest and over 20 weeks of storage in air at 0.5C. Overall, AFS1 transcript levels were closely correlated with accumulation of farnesene and CTols. In fruit of both cultivars, a sharp increase in AFS1 mRNA during the first 4 to 8 weeks of storage preceded a proportional rise in farnesene and a subsequent increase in CTols. However, maximum levels of AFS1 transcript, farnesene, and CTols were, respectively, 2.5-, 4-, and 33-fold greater in 'Law Rome' than in 'Idared' apples. Treatment of fruit of each cultivar with 1-MCP at harvest suppressed the increases in AFS1 transcript and farnesene early in storage, but AFS1 expression and farnesene synthesis had recovered in treated 'Law Rome' fruit after 20 weeks. The incidence of scald in untreated 'Law Rome' apples after 20 weeks at 0.5C plus 1 week at 20C averaged 86%, whereas 1-MCP treatment reduced the incidence to less than 1% and fruit of 'Idared' showed no scald regardless of the treatment.