Agriculture Reference
In-Depth Information
quantitatively expressed as GDH (growing degree hours) and GDD (growing de-
gree days). GDH is defined as 1 h at an actual temperature of 1 degree above a base
threshold of 5 and 10 °C in early blooming species (all the Rosaceae ) and in late
blooming species (kiwifruit, grape, etc), respectively. GDD (growing degree days)
is defined as the difference between the average daily temperature and the base
threshold define above. GDH are conveniently used from bud-break up to anthesis,
while GDD for fruit development up to ripening.
Climatological predictive models based on the dynamics of chill (chill unit-CU)
and heat (growing degree hours-GDH) accumulation have been developed.
The para-dormancy is defined by the reduced metabolic and morphogenetic
activity of one organ due to impediments external to the organ itself but within
the tree. The apical dominance referring to apical and lateral meristems or apical
and lateral buds relies on para-dormancy as all the correlative inhibitions existing
within the tree.
The main temperate fruit species belong to the Rosaceae family and include
pomefruit (apple, pear, quince), stonefruit (peach, nectarine, apricot, plum, almond,
etc.) as well as other species belonging to different families as walnut, hazelnut, pe-
can, pistachio, chestnut, olive, fig, persimmon, grape, strawberry, raspberry, black-
berry, blueberry, cranberry, currant and gooseberry, kiwifruit and some minor crop
as pomegranate, jujube, juneberry and the northern papaya. In Fig. 4.1 the acreages
and the yields of the main temperate fruit species are reported.
Main Temperate Fruit Species
The general climatic requirements are given below for the main temperate fruit
species.
Apple The domesticated apple (  Malus × domestica ) originated in the Caucasus
region of South-Eastern Europe and possibly South-Western Siberia is one of the
hardiest temperate zone fruits. The winter chilling requirement of the most com-
mercial varieties is indicatively 1,700 h. The growing season can be as short as 140
days for some varieties, thus extending its growing areas to the higher latitudes.
Pear European cultivated pear (  Pyrus communis ) probably developed through
selection of the wild pear (  Pyrus caucasica ) of South-East Europe, whereas
Asian cultivated pear derived from Pyrus pyrifolia and Pyrus ussuriensis . West-
ern pear varieties are somewhat less hardy than apple, so they cannot be grown
at high latitudes. The chilling requirement for most pears is ranging from 500
up to 1,500 h. The Pyrus pyrifoglia varieties and its hybrids usually require less
than1,000 h, thus are adapted to lower temperate latitudes. Pears perform well in
a warm to hat arid summer. Low humidity helps in controlling fireblight, a bacte-
rial disease caused by Erwinia amylovora , to which most pear and apple varieties
are susceptible. The growing season varies from 100 to 180 days depending on
the varieties.
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