Peel tissue a-farnesene and conjugated trienol concentrations during storage of ‘White Angel’× ‘Rome Beauty’ hybrid apple selections susceptible and resistant to superficial scald

In a 2-year study, fruit from eight redand eight yellow-skinned ‘White Angel’× ‘Rome Beauty’ hybrid selections were stored for 21 weeks at 0.5°C plus 1 week at 20°C and evaluated for the incidence and severity of superficial scald. Five red-skinned (R-03, R-20, R-22, R-48 and R-85) and three yellow-skinned (Y-26, Y-55 and Y-65) selections were examined in both seasons. Peel-tissue samples taken at 0, 7, 14 and 21 weeks of storage were analyzed for concentrations of a-farnesene and its conjugated trienol (CTol) oxidation products by HPLC with UV detection. Three red-fruited (R-44, R-48 and R-85) and five yellow-fruited (Y-38, Y-40, Y-55, Y-65 and Y-67) lines exhibited scald symptoms. The remaining lines (R-01, R-03, R-16, R-20, R-22, Y-07, Y-26 and Y-28) were free of scald. Overall, production of a-farnesene and accumulation of CTols were not closely correlated with scald susceptibility. Data for the selections most prone to scald, Y-65, Y-40 and R-44, were consistent with the proposed role of a-farnesene oxidation products in scald induction, but for Y-55 and R-48, which developed mild to moderate scald and accumulated very little CTols, the data conflicted with the a-farnesene oxidation–scald induction hypothesis. Also, scald-resistant lines Y-07 and R-22 produced high levels of a-farnesene and reached CTol concentrations comparable to those in several scald-susceptible lines. We conclude that if CTol do play a role in scald induction, there must be other mitigating factors of at least equal importance. Moreover, our findings support the proposal that oxidation products of a-farnesene are not essential for scald development in fruit with severely compromised antioxidative defenses, but free radicals and/or toxic volatiles generated by a-farnesene oxidation can exacerbate scald symptoms. © 2000 Published by Elsevier Science B.V.