Fig. 1. a-Farnesene concentration in peel tissue of ‘White Angel’ × ‘Rome Beauty’ selections at harvest as a function of
the log of the internal ethylene concentration IEC. Data points represent both red- and yellow-skinned lines from the
1997 and 1998 harvests. The polynomial equation derived from regression analysis was Y = 12.77 + 10.54X + 2.25X
2
, with an R
2
value of 0.478.
3. Results
3
.
1
. Relationship between a-farnesene and internal ethylene concentrations at har6est
In apples with IECs at or above log 0 ml l
− 1
, a
-farnesene concentrations increased with higher IECs Fig. 1. Although the R
2
for the relation- ship was low 0.478, few exceptions to the trend
occurred, and in fruit with IECs below log 0 ml l
− 1
the farnesene content was always B 10 mg kg
− 1
fresh weight.
3
.
2
. Incidence and se6erity of scald in relation to a
-farnesene synthesis and oxidation in red-skinned selections
Three of the eight red-fruited lines harvested in 1997 R-44, R-48 and R-85 developed scald after
21 weeks at 0.5°C plus 1 week at 20°C Table 1. Two of the scald-resistant SR lines R-01 and
R-16 were absent from the 1998 harvest, but the poststorage outcome was the same for the remain-
ing six lines; R-44, R-48, and R-85 exhibited scald and R-03, R-20 and R-22 did not. For both R-44
and R-48, the percentage of scalded fruit and scald severity were similar in the 2 years, whereas
for R-85, the number of scalded fruit was much lower in 199899 than in 199798.
R-44 was clearly the most scald-prone red- skinned selection, with incidence \ 90 and
about one-third of the fruit surface affected in both years.
In both SR and scald-susceptible SS red- skinned selections, peel a-farnesene levels gener-
ally peaked at 7 weeks in fruit harvested in 1998 and at 14 weeks in those harvested in 1997 Fig.
2. Also, among the selections harvested in both years, total a-farnesene accumulation was greater
in 199899 in SR fruit, but not in SS fruit. Of the lines that produced the most a-farnesene, peak
concentrations were at least as great in peel of SR lines R-20 and R-22 as in peel of SS lines R-48
and R-85. In R-44, the red-skinned selection most prone to scald, peel concentrations of a-farnesene
were only determined in 199899 and were consis- tently lower than in R-48 or R-85 that year.
Fig. 2. a-Farnesene concentration in peel tissue of scald-resis- tant and -susceptible red-skinned selections over 21 weeks at
0.5°C in air. Closed and open symbols indicate fruit from the 1997 and 1998 harvests, respectively. Data points represent the
average of two replicate analyses; variation between replicates was generally less than 10 except for values 5 10 mg kg
− 1
fresh weight.
B .D
. Whitaker
et al
. Posthar
6 est
Biology and
Technology
20 2000
231 –
241
235 Table 1
Scald evaluation in red- and yellow-skinned ‘White Angel’בRome Beauty’ selections after 20 weeks at 0.5°C in air plus 1 week at 20°C, and relative a-farnesene and conjugated trienol CT levels in peel tissue over the course of storage
199798 Harvest and storage 199899 Harvest and storage
Hybrid Hybrid
Scald percent Scald severity
Scald percent Scald severity
a -Farnesene
CTs a
-Farnesene CTs
selection selection
Red fruit –
– c
01 –
– 0.0
Very low Mod. High
c 01
Very low c
03 0.0
Moderate Very low
c 03
0.0 Low
– –
– –
c 16
Very low c
16 0.0
Low 0.0
Very high Mod. low
c 20
0.0 High early
Mod. Low c
20 0.0
Mod. high Mod. high
c 22
c 22
High late High late
0.0 92
2.5 Moderate
c 44
Mod. high 98
2.5 Not analyzed
Not analyzed c
44 19
1.9 Mod. high
Very low c
48 Very low
c 48
27 1.9
Mod. high c
85 4
63 1.8
Mod. high Very high
1.3 Very high
Very high c
85 Yellow fruit
High c
07 –
– –
– 0.0
c 07
Very high 0.0
Moderate Very low
c 26
c 26
Low Very low
0.0 c
40 100
4.0 Very high
Moderate 0.0
Mod. high c
28 Low
47 1.8
Mod. high Moderate
c 67
Mod. low Very high
c 38
35 1.1
c 55
70 54
1.0 Very low
Very low 1.4
Very low Very low
c 55
Very high c
65 76
2.0 Mod. low
Very high c
65 100
3.5 High early
Fig. 3. Conjugated trienol concentration in peel tissue of scald-resistant and -susceptible red-skinned selections over 21
weeks at 0.5°C in air. Closed and open symbols indicate fruit from the 1997 and 1998 harvests, respectively. Data points
represent the average of two replicate analyses; variation be- tween replicates was generally less than 10 except for values
5
2 mg kg
− 1
fresh weight.
lated no more than 6 mg kg
− 1
of CTols in either storage season. Most red-skinned SR selections
did not exceed 6 mg kg
− 1
CTols throughout storage, but fruit of SR line R-22 reached 13 –
15 mg kg
− 1
CTols in both years, comparable to levels in highly SS line R-44 fruit. The pattern of
CTol accumulation in peel of R-22 fruit was quite different in the two seasons and reflected the
different pattern of a-farnesene accumulation Fig. 2. Both a-farnesene and CTols began to rise
much sooner, and peaked 7 weeks earlier, in 199899 than in 199798.
3
.
3
. Incidence and se6erity of scald in relation to a
-farnesene synthesis and oxidation in yellow-skinned selections
Five of the 8 yellow-fruited lines tested Y-38, Y-40, Y-55, Y-65 and Y-67 developed scald
Table 1. One SR line Y-28 and 1 SS line Y-38 included in the 199798 storage experiments were
replaced by two other SS lines Y-40 and Y-67 in 199899. The SR selection Y-26 exhibited no scald
in both years. Of the 3 SS lines examined in only one season, the incidence and severity of scald
were extreme in Y-40 199899, intermediate in Y-67 199899, and relatively low in Y-38 1997
98. SS lines Y-55 and Y-65 were harvested in both years, and for each of them, the incidence
and severity of scald were greater in 199798 than in 199899. Scald was more extensive in Y-65 than
in Y-55 fruit, the incidence and severity index averaging 88 and 2.8, and 62 and 1.2,
respectively.
As noted for red-skinned selections, a-farnesene content tended to increase earlier in yellow-
skinned fruit harvested in 1998 compared with those harvested in 1997 Fig. 4. However, the
two SS lines that were harvested in both years, Y-55 and Y-65, did not show this trend. In con-
trast, the only SR selection harvested in both years produced much more a-farnesene in 199899
than in 199798. The a-farnesene content of both SR and SS yellow-skinned selections varied con-
siderably. Fruit of the most acutely SS line, Y-40, showed the earliest rise in a-farnesene and main-
tained the highest levels throughout storage, whereas fruit of the moderately SS line Y-55 had
Overall, peel tissue CTol levels were somewhat higher in SS than in SR red-skinned selections
Fig. 3. However, both groups included lines with relatively high and relatively low concentrations
of CTols. SS line R-85 accumulated the most CTols among red-skinned selections. In R-85 fruit
harvested in 1998, the rate of CTol accumulation increased throughout storage and CTol concen-
tration peaked at 27 mg kg
− 1
at 21 weeks, whereas in 1997, CTols accumulated most rapidly
from 7 to 14 weeks and reached a maximum of 18 mg kg
− 1
at 21 weeks. Peel CTols in fruit of the most highly SS line, R-44, increased linearly
for 14 weeks to a peak level of 15 mg kg
− 1
then declined. Fruit of R-48, which had a 19 – 27 incidence of moderate scald Table 1, accumu-
Fig. 4. a-Farnesene concentration in peel tissue of scald-resis- tant and -susceptible yellow-skinned selections over 21 weeks
at 0.5°C in air. Closed and open symbols indicate fruit from the 1997 and 1998 harvests, respectively. Data points represent
the average of two replicate analyses; variation between repli- cates was generally less than 10 except for values 5 10 mg
kg
− 1
fresh weight.
scald were lesser, in 199899 than in 199798 Table 1. The most acutely SS line, Y-40, and the
moderately SS line Y-67 had similar, moderate peel CTol levels throughout storage, with maxima
at 21 weeks of 6 and 8 mg kg
− 1
, respec- tively. The pattern and final level of CTol accu-
mulation in peel of SR line Y-07 were almost identical to those in peel of SS line Y-67, although
the data were from different years. SR line Y-26 in both years, and SR line Y-28 in 199798, did
not exceed a peel CTol content of 3 mg kg
− 1
. Finally, and most notably, in accord with their
low production of a-farnesene Fig. 4, fruit of moderately SS Y-55 accumulated no more than 1
mg kg
− 1
CTols throughout storage in both years.
Fig. 5. Conjugated trienol concentration in peel tissue of scald-resistant and -susceptible yellow-skinned selections over
21 weeks at 0.5°C in air. Closed and open symbols indicate fruit from the 1997 and 1998 harvests, respectively. Data
points represent the average of two replicate analyses; varia- tion between replicates was generally less than 10 except for
values 5 2 mg kg
− 1
fresh weight.
the lowest a-farnesene levels after 21 weeks of any of the ‘White Angel’ × ‘Rome Beauty’ selections.
In addition, among the selections harvested in 1997, the rate and extent of a-farnesene accumu-
lation in SR lines Y-07 and Y-28 were comparable to those in SS line Y-38.
Peel tissue CTol levels were generally higher in SS than in SR yellow-skinned selections Fig. 5.
However, among the SS lines there was wide variation in the production and peak level of
CTols. Highly SS line Y-65 accumulated the most CTols of any yellow-skinned selection in both
years, with a maximum concentration of 15 – 18 mg kg
− 1
at 21 weeks. It is noteworthy, though, that the rate and final level of CTol accumulation
were greater, but the incidence and severity of
3
.
4
. Comparison of a-farnesene and CTol concentrations determined by HPLC – UV analysis
and spectrophotometric estimation Using aliquots from the same peel tissue hexane
extracts, a-farnesene and CTol values calculated by the UV absorbance method Anet, 1972 were
compared with those determined by HPLC – UV analysis Whitaker et al., 1997. Data for three
representative scald-susceptible yellow-skinned se- lections Y-40, Y-55 and Y-65, which include
values in the low, moderate, and high ranges, are shown in Fig. 6.
a -Farnesene concentrations determined by the
two methods were generally quite similar. For Y-40, which had the highest a-farnesene levels of
any selection, spectrophotometric values were typ- ically 5 – 10 higher than HPLC values. Con-
centrations of CTols determined by the two methods did not differ substantially for Y-65,
which had the highest CTol levels among the yellow-skinned selections, but were markedly dif-
ferent for Y-40 and Y-55. Hexane extracts from these two lines, which accumulated very low Y-
55 to low-moderate Y-40 levels of CTols, gave UV-absorbance-derived values that were from
1.4- to 6.2-fold higher than those obtained by HPLC – UV analysis.
4. Discussion
