Agriculture Reference
In-Depth Information
An inverse relationship between average annual precipitation and TA in grape-
fruit juice has been reported. Similarly, heavy rainfall in the 2 months prior to har-
vest can significantly reduce TA and TSS content in Clementine mandarins and
'Valencia' orange juice. Rainfall also affects fruit shape and peel thickness. Some-
times, and on an irregular basis, hail damage occurs in citrus-growing areas. The
extent of the damage depends on the size of the hailstones, but the peel may get
slightly pitted, deeply sunken or even dramatically broken.
Citrus trees have high shade tolerance, but maximum yields are produced under
high light intensity. There is a correlation between smaller fruit sizes and the high
percentage of cloudy days through the spring. Total soluble solids concentration in-
creases with higher light intensity, and the vitamin C content in the juice can vary
with exposure of the fruit to light, with the outside fruit having the highest content.
However, juice content of the fruit can decrease with exposure to increasing light in-
tensity. Peel colour is also affected by light, which is necessary for carotenoid and an-
thocyanin synthesis, with exposed fruits more coloured than those exposed to shade.
Citrus fruits are highly resistant to insolation (sunburn) injury. Temperature
as high as 44.4 °C is necessary to cause sunburn injury in 'Valencia' whereas the
'Murcott' tangerines and some early maturing Clementine mandarins are peculiarly
susceptible to sunburn.
Wind can have a definitive limiting effect on citrus production and quality. Wind
injuries have been recognized as the major abiotic factor contributing to peel dam-
age worldwide. Wind speeds above 24 km h
−1
have been considered potentially
damaging. Wind injuries take the form of an irregular brown spots, which normally
affect only the flavedo or the outer colored layer of the mesocarp of a citrus fruit.
Intensity of the injury depends on wind speed, varietal sensitiveness, the presence
and size of thorns, the leaf roughness, and the size of fruit.
Flowering
In subtropical regions,
Citrus
has three flushes of shoot development, early in
spring, after physiological fruitlet drop, and later in summer, with bloom occurring
during the spring flush (Fig.
6.2
). In tropical climates, however, bud sprouting and
flowering take place throughout the year, although the main bloom also occurs in
spring.
Citrus
species produce leafy and leafless flowered shoots, the number of both
flowers and leaves varying among them. Thus, there are single-flowered and multi-
flowered leafy and leafless shoots, and vegetative shoots (Fig.
6.3
).
The proportion of each type of shoots depends on the species and varieties. For
example the Satsuma mandarin group produce only single flowered shoots and veg-
etative shoots.
Citrus species have 2-5 years period of juvenility in which trees are unable to flow-
er. Afterwards, citrus trees usually produce larger number of flowers than they need
to achieve optimum yields. However, in some cases, competition among developing
