Agriculture Reference
In-Depth Information
temperature (30-35 °C and above) may drastically reduce or fully inhibit lycopene
production in tomatoes. Liptay et al. (
1986
) stated that seasonal variations in the
ascorbic acid content of the tomato cv. 'Jumbo' fruit ranged from 70 to 230 mg kg
−1
fresh mass at the mature-green stage, and are directly correlated with temperature
variations, when grown under greenhouse conditions.
Pardossi et al. (
2000
), Islam and Khan (
2001
), and Kano (
2004
) reported that
sugar accumulation can be suppressed by high air temperatures when growing
melons, cherry tomatoes, and watermelon, respectively. Moreover, preharvest tem-
peratures can influence harvest quality and postharvest deterioration. For example,
Kang et al. (
2002
) reported that cucumber fruit grown at a high average day tem-
perature of 32 °C had a storage life of 16 days at 10 °C and did not exhibit chilling
injury, whereas fruit grown at 27 °C developed symptoms of chilling injury after 12
days, at 10 °C. In addition during storage, firmness, vitamin C content, activity of
superoxide dismutase, and catalase were higher in high temperature grown fruits
than in control fruits.
Root-Zone Temperature
Root temperature is also known to have an effect on plant growth and product qual-
ity. Optimum root temperatures are known to stimulate constant new root growth
and improve the uptake of nutrients and water in hydroponic or substrate culture
systems, during the rapid development stage of the tomato, bell pepper, and cucum-
ber fruits (Schnitzler and Gruda
2002
).
Calatayud et al. (
2008a
) found that rose roots growing in cold solution (10 °C)
were thin, white, succulent, short and sparsely branched, whilst in warm solution
(22°C) roots were long, brown, thick and branched. In addition Kafkafi (
2001
)
showed that at the same water potential gradients, and at constant light radiation and
air humidity as well as canopy temperature, the rate of water flow through the stem
in tomato was increased by 250 % when root temperature changed from 12 to 20 °C.
Studies with lettuce grown in a floating hydroponic system have shown that
the head size, leaf color and thickness, as well as root structure, developed best at
24 °C water temperature, regardless of air temperature. Keeping water temperature
at 24°C maintained the market quality of lettuce heads even at 31 °C air tempera-
ture (Thompson et al.
1998
). Benoit and Ceustermans (
2001
) and Li et al. (
2002
)
reported a much lower rate of BER of soilless culture sweet pepper plants grown on
cooled slabs than on non-cooled slabs, possibly due to a higher root activity from
better oxygen content in the root environment.
Suboptimal stress, on the other hand, can be used to improve the quality of veg-
etable seedlings. Chen et al. (
1999
), reported shorter and more compact plug-grown
seedlings, which were irrigated with cold water (tomatoes 5-15 °C, cabbage 5 °C)
compared with actively growing warm-season plants, e.g. cucumber, where irriga-
tion with too much cold water sometimes cause irreparable damage from cold shock
(Fig.
10.12
).
