Submitted to: Postharvest Biology and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/4/2006
Publication Date: 4/15/2006
Citation: Gapper, N.E., Bai, J., Whitaker, B.D. 2006. Inhibition of ethylene-induced a-farnesene synthase gene PcAFS1 expression in ‘d’Anjou’ pears with 1-MCP reduces synthesis and oxidation of a-farnesene and delays development of superficial scald. Postharvest Biology and Technology. 41:225-233. DOI: 10.1016/jpostharvbio.2006.04.014. Interpretive Summary: A disorder called scald occurs in many popular varieties of apples and pears, appearing as sunken brown patches on the skin that make the fruit unmarketable. Since scald often does not appear until after removal from cold storage, it can cause great loss of fruit after all the expense of growing, harvesting, and storing them. This study was conducted to find out if scald development in pears and apples involves the same basic mechanism. It also tested treatment of pears with a new food-safe chemical, 1-MCP, that is known to control scald in apple fruit. Our results showed that in pear, as in apple, scald is induced when the gene AFS1 is turned on in the cold-stored fruit. This leads to accumulation of a natural toxic chemical that eventually kills the peel tissue. Treatment of apples with 1-MCP blocks the switch that turns on AFS1 and thus prevents scald. We found this was also true for pears, but a dose of 1-MCP high enough to control scald also inhibited ripening. This work provided information that can be used by plant scientists to develop new scald-resistant varieties of apple and pear fruits. It also identified the need for further study before 1-MCP treatment can become a practical means of scald control in pear fruit by fresh fruit growers and distributors.
Technical Abstract: Pre-storage treatment of scald-susceptible apple and pear fruits with the blocker of ethylene action 1-methylcyclopropene (1-MCP) inhibits the synthesis of a-farnesene. Consequently, accumulation of a-farnesene and its conjugated trienol (CTol) oxidation products in the fruit skin is diminished, and superficial scald is largely prevented. In cold-stored apple fruit, a marked increase in expression of AFS1, the gene encoding a-farnesene synthase (AFS), precedes the rapid accumulation of a-farnesene. A Pyrus communis gene encoding AFS (PcAFS1) was cloned using RT PCR with primers based on apple AFS1 and RNA from peel tissue of d’Anjou pears cold-stored for 33-94 days. Non-treated control and 1-MCP-treated (300 ppb for 6 h at 1 C) pears were stored at –1 C in air for up to 216 days. PcAFS1 expression in control fruit increased sharply over the first 63 days, was constant from 63-157 days, and then increased again from 157-183 days. In comparison, expression of PcAFS1 in 1-MCP-treated fruit was attenuated; levels PcAFS1 transcript were about 8-fold, 2.5-fold, and 2.3-fold lower than in the controls at 63, 123, and 183 days of storage, respectively. Maximum concentrations of a-farnesene and CTols in control fruit occurred at 94 and 123 days, respectively, and scald incidence was 100% after 94 days. a-Farnesene and CTol levels at these time points were, respectively, 9- and 19-fold lower in 1-MCP-treated fruit, which had no scald at 157 days, 13% at 183 days, and 40% at 216 days. Post-storage ripening, with the associated increases in softening, respiration, and ethylene production, was fully enabled in control fruit after 63 days at –1 C, whereas 1-MCP-treated pears failed to ripen properly even after 216 days.