Agriculture Reference
In-Depth Information
16.2 WEATHER VARIABLES AND ITS EFFECT ON FRUIT
QUALITY
16.2.1 TEMPERATURE
Fruit crops are sensitive to temperature and each plant species has its own
characteristic response to temperature. They have specific temperature re-
quirements for growth, higher yield and quality. Increase in atmospheric
temperature affects photosynthesis directly, causing alterations in sugars,
organic acids, firmness, flavonoids contents and antioxidant capacity of
fruits. High temperature reduces the net carbon gain in crops, particularly
in C
3
plants, by increasing photorespiration.
Higher temperature on fruit surface caused by prolonged exposure to
sunlight hastens ripening and other associated events. Grapes exposed to
direct sunlight ripened faster than those ripened in shaded areas within
the canopy. This delay in ripening is associated with reduced cell wall en-
zyme activity (cellulose and polygalacturonase) due to high temperature.
However, this delay did not occur via a direct effect on the enzymes as-
sociated with cell wall degradation. Fruit firmness is also affected by high
temperature conditions during growth. Changes in cell wall composition,
cell number and cell turgor properties were postulated as being associated
with the observed phenomenon.
Temperate fruit crops require sufficient accumulated chilling or vernal-
ization to develop fruitful buds and break winter dormancy in the spring.
Inadequate chilling due to enhanced greenhouse warming may result in
prolonged dormancy, leading to reduced fruit quality and yield. Flavor of
the fruit is also affected by temperature. Flavor is dependent on the bal-
ance between organic acids (citric, malic, tartaric acid, etc.) and sugars (su-
crose, fructose, and glucose). Fruits like apple exposed to direct sunlight
develop higher sugar content compared to those fruits grown on shaded
sides of the canopy (Brooks and Fisher, 1926). In case of grapes, high
temperature during growing season increases sugars and decreases tartaric
acid content (Kliewer and Lider, 1970). It is reported that an increases in
10°C temperature lead to 50% reduction in tartaric acid content. Moisture
content of 'Hass' avocados were found to be increased when grown un-
der higher temperatures (45±2°C), than comparatively lower temperatures
(30±2°C) (Woolf et al., 1999). The concentration of specific fatty acids
also increased (e.g., palmitic acid by 30%) at higher temperatures.
