Agriculture Reference
In-Depth Information
Due to solar radiation and the “greenhouse effect” temperatures could sometimes
rise above the optimal level for plant growth and development. Under such condi-
tions many horticultural crops are exposed to a heat stress situation. Deleterious
effects of high temperature can be direct or indirect. Direct temperature can damage
cellular membranes, proteins, and nucleic acids. Indirect temperature effects can
include inhibited pigment synthesis and thermal degradation of existing pigments as
a result of sun scald or systems of sun burn (Kays
1999
) as well as desiccate tissue
and plant organs induced by water stress. In this case, internal fruit and vegetable
temperature is more important than air temperature.
Physiologically high temperatures influence the photosynthesis process by in-
ducing stomatal closure, increasing the rate of respiration and resulting in lowered
biomass production and yield. Air temperatures do not only have an effect on plant
growth and yield, but rather affect the development processes at different develop-
ment phases. High temperatures result in “heat delay” a term that characterizes the
effect of temperature, on delaying flower initiation. First in line are high night tem-
peratures, but also day temperatures above the optimum for given species and cul-
tivar leading to flowering delays. Warner and Erwin (
2005
), for instance, reported
that high temperatures of 32 °C reduced the number of flower buds and resultant
flowering in five annual herbaceous ornamentals, regardless of DLI.
Pollination, fruit set formation and horticultural products quality, are influenced
by extreme high temperatures (Gruda
2005
). For instance, Sato et al. (
2002
) re-
ported that a continuous temperatures of 32/26 °C (day/night) led to the disruption
of development in the pollen, endothecium, epidermis and stomium of anthers of
tomato plants. Similar day/night temperatures reduced the percentage of germinated
pollen of pepper plants compared with those at normal temperatures (26/22 °C) as
well as fructokinase activity in mature pollen (Karni and Aloni
2002
). Pollen grain
release and germination has of course an effect on the ability of plants to set fruits.
Abdelmageed and Gruda (
2009
) reported that heat stress associated with high day
temperatures of 37 °C markedly decreased fruit fresh weight and the percentage of
fruit set of tomatoes, as well as increasing the proportion of parthenocarpic fruits
and aborted flowers. On the other hand reducing night temperatures from 27 to
22 °C had a positive effect on the number of pollen grains produced and released
and fruit set percentage in the tomato. These results concur with Peet et al. (
1997
)
who showed that low or optimal night time temperatures could compensate for high
daytime temperatures in influencing pollen grain production in the tomato.
A combination of increased daily radiation and temperature has increased the in-
cidence of blossom-end-rot (BER) of tomatoes, pepper and eggplant and tipburn of
Chinese cabbage and lettuce. Taste, flavor and nutraceutical compounds of fruit and
vegetables, grown under protected areas are also influenced by temperature. Gruda
(
2005
) and Castilla and Hernandez (
2007
) reported that high temperatures can limit
tomato fruit acidity, negatively influence taste and flavor, develop poor color and
exhibit low lycopene content. Gross (
1991
) has shown that the optimal temperature
range for lycopene formation in the tomato is between 16 and 21 °C, whereas tem-
peratures between 12 and 21 °C favor best tomato fruit color (Dorais et al.
2001
).
However, both Dorais et al. (
2001
) and Dumas et al. (
2003
), agree that very high air
