Agriculture Reference
In-Depth Information
of growth more than 170% higher than those at 400 ppm. When the trees
grown older and are matured, this CO
2
induced enhancement lowered to
approximately 100%. However, 127% increase in orange production was
recorded from the trees under 700 ppm CO
2
exposure. Experiments have
also shown that stomata conductance of C3 plants is initially reduced with
elevated CO
2
, leading to reduced transpiration and increased conservation
of water (higher carbon assimilation per water lost); but, such responses
are short- lived in some species (Bunce, 1992). Increased CO
2
has also
been reported to ameliorate the negative effects of drought stress (Tolley
and Strain, 1985).
2.5
FRUIT QUALITY
Temperature is an important factor that affects anthocyanin biosynthesis
in plants. The expression of anthocyanin biosynthetic genes has been in-
duced by low temperature. However, it has been repressed by high tem-
perature in various plants such as apple (Ubi
et al.,
2006), grape (Yamane
et
al.,
2006) and red oranges (Lo Piero
et al.,
2005). In grapes, high tem-
peratures above 115 °F cause thick skin of berries. Similarly, higher night
temperatures reduce anthocyanin accumulation in berry skin and the de-
crease in anthocyanin accumulation under high temperature results from
factors such as anthocyanin degradation as well as the inhibition of mRNA
transcription of the anthocyanin biosynthetic genes (Mori et al., 2005). In
ripening apples, anthocyanin's are apparently induced at low temperatures
(<10 °C) (Curry, 1997) while synthesis takes place under high irradiation
at mild temperatures (20 °C to 27 °C) in detached, mature apples (Curry,
1997; Reay, 1999).
High temperatures results in poor red peel color development of apples
(Wand et al., 2002, 2005). Felicetti and Schrader (2008) reported three
types of sun-burn: a disorder that occurred due to heat and or light stress.
The first type is sun-burn necrosis and is heat-induced when the tempera-
ture of fruit surface reaches 126 °F for 10 min. It induces thermal death
of cells in the peel followed by a necrotic (dark brown or black) spot. The
second type of sun-burn is sun-burn browning and it is the most common
type, which results in a yellow, brown, or dark tan spot on the sun exposed
side of the fruit. Third type of sun-burn is induced when fruits are sud-
denly exposed to full sun light. These apples have been shaded earlier and
