Agriculture Reference
In-Depth Information
Table 10.2
Effects of EC and application timing of EC on lycopene content of tomato fruits at
different ripeness stages. (According to Wu and Kubota
2008a
)
Treatment
Lycopene concentration (mg g
−1
DW)
G B and T P and LR R
High EC ND 0.07 0.39 a 1.39 a
Delayed high EC ND 0.10 0.32 b 1.29 a
Low EC ND 0.08 0.25 c 0.99 b
ANOVA (
P
= 0.05) - NS * *
The six fruit ripeness stages characterized by color development, which include green (G), breaker
(B), turning (T), pink (P), light red (LR) and red (R) (USDA 1976). Low and high EC were 2.3
and 4.5 dS m
−1
, respectively. The high EC and the delayed high EC treatments were applied imme-
diately after anthesis and 4 weeks after anthesis, respectively. ANOVA, Analysis of Variance for
treatment significance: * or NS at
P
= 0.05. Means with the same letters are not significantly differ-
ent according to a Tukey HSD test at
P
= 0.05. NS = no significance. ND = not detected. DW = dry
weight (Source: Wu and Kubota
2008a
)
lycopene content of tomato,
cv
. 'Durinta', increased 12-20-fold as fruits developed
from the breaker/turning stages to the red stage (Table
10.2
).
Wu and Kubota (
2008a
) suggested that ethylene synthesis triggered by osmotic
and/or salt stress is central to the increase in lycopene concentration within the to-
mato fruit. The reduced water flux is linked to an increase in TSS and under these
environmental conditions tomatoes mature earlier and accumulate more lycopene
during the pre-harvest time.
Similar results, where an increased EC-value enhanced health-promoting sub-
stances, were also obtained for sweet pepper, cucumber (Sonneveld and van der
Burg
1991
; Trajkova et al.
2006
), eggplant (Savvas and Lenz
1994
), celery (Pardossi
et al.
1999
), watermelon (Colla et al.
2006
), as well as zucchini squash (Rouphael
et al.
2006
). Seo et al. (
2009
) reported that the EC-value of the nutrient solution
as well as the concentration of S and P can strongly influence the concentration of
sesquiterpene lactones; and therefore have an effect on bitterness and acceptability
of lettuce.
Adjusting the salinity of the nutrient solution allows growers to modify water
availability to the crop and hence improve the quality of tomato fruits. However,
increasing the salinity, limits marketable yield, increases the incidence of BER, and
reduces fruit size (Dorais et al.
2001
; Gruda
2009
). For instance, although cherry to-
matoes are considered to be more tolerant in respect to adverse effects of EC-values,
the total yield of cherry tomatoes was reduced at a higher salinity (6 dS m
−1
) in
comparison to 3 dS m
−1
(Serio et al.
2004
). One of the disadvantages of increasing
TSS by a high EC treatment is the reduction in fruit size due to a reduction of water
content in the fresh fruit (Adams and Ho
1989
) where fruits were smaller, mainly
due to a reduction in fresh weight (Ehret and Ho
1986
). This resulted in total yield
reductions and an increased occurrence of the physiological disorder blossom-end
rot (BER) (Petersen and Willumsen 1991), caused by a reduction of calcium absorp-
tion by the roots and increased resistance to xylem transport inside the fruit (Ho and
Adams
1989
). According to Ho et al. (1999), accelerated fruit enlargement may be
