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William J. Bramlage

Preharvest temperature (hrs. below 10°C) is a predictor of scald development on North American apples after long-term storage. In Mass., these variables are highly negatively correlated for both `Delicious' and `Cortland' apples. However, this predictor was not generally applicable for scald development on `Delicious' or `Granny Smith' apples in New Zealand. There, the relationship between temperature and scald varied greatly among districts for both cultivars, with scald resistance often occurring with far fewer hrs. below 10° than in Mass. Yet, in two cases when the temperature: scald relationship for `Granny Smith' was similar to that for `Cortland' and `Delicious' in Mass., temperature patterns during fruit ripening were similar to that in Mass. In all other cases, more moderate temperature changes occurred. These results suggest that the true base temperature for developing resistance to scald may be between 10° and 15°C, rather than 10°.

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William J. Bramlage

`Cortland' and `Delicious' apples were stored at 0C for up to 25 weeks, and at 20C in either open boxes or non-sealed poly bags for up to 8 weeks. At 20C, lesions occurred mostly around lenticels, but with some calyx bronzing and scald-like symptoms on shaded areas. At 0C, typical scald symptoms occurred. At both temperatures, high concentrations of alpha-farnesene and conjugated trienes occurred in conjunction with symptom appearance, and both these concentrations and discolorations decreased with later harvest of fruit. Scald development appeared to be chilling-enhanced, but not chilling-dependent.

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Zhanyuan Du and William J. Bramlage

When Cortland apples were stored at 0 and 20C, 0C reduced ethylene production and increased accumulations of ∞-farnesene and conjugated trienes (CTs) in fruit peel, but it resulted in a lower CT258: CT281 ratio than did 20C. At 20C no fruit developed scald, but at 0C, 84% of the fruit scalded. When fruit were stored at 0C but transferred to 20C for 5 days after 0 to 8 weeks at 0C, only transfer after 2 or 4 weeks reduced scald. During warming, ethylene production and accumulations of ∞-farnesene and CTs increased, but after 20 weeks of storage, when scald developed, warming at 2 and 4 weeks reduced CT281 and increased the CT258: CT281 ratio. Warming at other intervals had no effect.

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Zhanyuan Du and William J. Bramlage

Three experiments were conducted using `Cortland' and `Delicious' apples (Malus domestica Borkh.). Fruit varying widely in superficial scald susceptibility, because of either endogenous or experimentally induced conditions, were stored for various intervals at 0C and evaluated for scald development at 20C. Samples were extracted periodically in hexane, and ultraviolet absorption spectra of the extracts were used to evaluate α-farnesene and conjugated triene (CT) relationships to scald development. CT concentrations were calculated using each of the three CT absorption maxima (258-290 nm, 269-290 nm, and 281-290 nm) and expressed accordingly as CT258, CT269, and CT281. The poor association of CT281 concentrations with scald development led us to propose that metabolic products of CT281 species are more likely to be associated with scald development than the species themselves.

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Zhanyuan Du and William J. Bramlage

Much correlative data support the hypothesis that superficial scald on apples results from oxidation of α farnesene to conjugated trienes (CT) in the coating of apples. However, these associations are poorly defined both chemically and physiologically. α Farnesene and CT are measured as OD 232 and OD 281-290, respectively, of a hexane extract of the fruit surface. During assays, we observed anomalies in absorbance characteristics of extracts from fruit with different scald potentials, particularly in the region of 258 nm. Results suggest that absorbance near 258 nm might represent a metabolite of CT, which may be further metabolized. It appeared that under different conditions, CT metabolism could be altered, resulting in changed ratios of OD 258/OD 281. Higher ratios correlated with lower scald development, regardless of CT concentration. Thus, CT metabolism, rather than its concentration, may determine if scald occurs.

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Zhiguo Ju and William J. Bramlage

Influences of fruit maturity, AVG and ethephon preharvest treatments, and storage conditions on cuticular phenolic concentration, α-farnesene accumulation and oxidation, and scald development of `Delicious' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] were studied. Advanced maturity and ethephon treatment increased free phenolics in fruit cuticle at harvest, while AVG treatment caused a reduction. Free cuticular phenolics increased during early storage in ethephon-treated and nontreated fruit but not in AVG-treated apples. Advanced maturity and ethephon did not alter α-farnesene accumulation overall, but reduced conjugated triene (CT281) formation and scald development. When stored in a low-ethylene room (<1 μL·L-1), AVG-treated fruit accumulated very low levels of α-farnesene and CT281 and did not develop scald after 6 months at 0 °C. When stored in a commercial room (ambient ethylene >5 μL·L-1), the AVG-treated and control fruit accumulated similar amounts of α-farnesene and CT281 and developed similar percentages of scald. In general, free phenolic concentrations in fruit cuticle were negatively correlated with CT281 formation and scald development of apples. Chemical names used: aminoethoxyvinylglycine (AVG); 2-chloroethylphosphonic acid (ethephon).

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Zhanyuan Du and William J. Bramlage

Ethephon treatments had two opposing effects on scald induction. First, synthesis and metabolism of α- farnesene were immediately enhanced, which could increase scald development. Second, during prolonged storage the relative concentrations of two conjugated triene forms (CT281 and CT258) were altered so as to increase the CT258/CT281 ratio, which could reduce scald development. The balance between these responses determined whether ethephon increased or decreased scald. DPA treatment also had two effects, immediately suppressing ethylene and α- farnesene concentrations, and over long periods, suppressing CT281 but increasing CT258 concentrations. Both effects of DPA appeared to reduce scald development. Effects of DPA, as well as of ethephon, were at least partly ethylene - mediated, and treatment with DPA counteracted effects of an ethephon treatment.

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Zhiguo Ju and William J. Bramlage

Cuticle provides a barrier for secretory of volatile lipophilic metabolites like α-farnesene in fruit. The accumulation and oxidation of α-farnesene or the propagation of its oxidation products can be affected by the thickness, the constituents, and the structure of this cuticle. To measure the development changes of cuticle components, `Delicious' trees were treated separately with 250 ppm aminoethoxyvinylglycine (AVG) on 12 Sept. and 200 ppm ethephon on 19 Sept. Fruit were harvested on 28 Sept. and stored at about 20C for 6 weeks. Total wax in both treatment and control fruit at harvest was around 2.8 mg/f.fr.wt. It increased rapidly after 2 weeks and reached 8.4 mg/g fr.wt. in control fruit after 6 weeks, which paralleled increasing internal ethylene and accumulation of α-farnesene. Ethylene synthesis, α-farnesene, and total wax accumulation were enhanced by ethephon treatment and completely suppressed by AVG treatment during the whole period of storage. The cutin contents in fruit from treated fruit and the control were similar at harvest, and they remained constant during storage.