Agriculture Reference
In-Depth Information
15.1 INTRODUCTION
Pyrus
L. is a member of the subtribe Pyrinae, tribe Pyreae, subfamily Spiraeoideae
(formerly Maloideae), family Rosaceae. Among the widely distributed in Euro Asia,
40 species of the genus
Pyrus
,
Pyrus communis
L., and
P. pyrifolia
(Burm.) Nak.
are the main edible pear species; however,
P. communis
are
of the greatest economic
value [1]. Most cultivars, grown in temperate zones, were created from this species.
Many researchers identify intraspecific taxon—
P. communis
subsp.
domestica
(Me-
dik.) Domin [2]—which enumerates over five thousand pear cultivars [3], and only
a small percentage of them are cultivated commercially [4]. Pear cultivars grown in
Japan, China, and other countries of Eastern Asia belong mostly to
P. pyrifolia
[1, 4].
About seven percent of pears are grown in commercial orchards of Ukraine, and
15 percent—in home orchards. According to this indicator, pears are second after ap-
ples; the latter occupies 75 and 40 percent of the areas allocated for fruit and berry
crops, correspondingly. Last decade witnessed a positive tendency in pear produc-
tion in compliance with a national program of horticulture development in Ukraine
approved in 2008; it is planned to increase pear orchards to 20.8 thousand ha for the
period up to the year of 2025 [5].
At present, Ukraine is among the top twenty world pear producers; its annual har-
vest is 102-177 thousand tons (metric tons), and it is the best index for former So-
viet Union countries. Last decade showed an increasing tendency of worldwide pear
production from 8 897 thousand tons in 2001 to 15 945 thousand tons in 2011. This
tendency is true for Ukraine except for quite unstable pear production in various years
[6]. With this in view, the requirements of quantity and quality are higher, including
unifi cation of planting pears; it also explained the necessity to do research concern-
ing the improvement of advanced vegetative propagation of both cultivars and clonal
(vegetatively propagated) pear rootstocks and their close wild relatives, which can be
used in a pear-breeding program.
Pear is an allogamous plant and, as a result, economic and other features are not
preserved when seed propagation is used. Thus, only vegetative propagation, includ-
ing clonal pear rootstocks, can provide unifi ed planting pears. All methods of vegeta-
tive propagation are associated with plant damage; they are based on the plants' ability
to regenerate, which in turn defi ned the subject/direction of our research.
Various localized damages occur on the plants (especially perennial plants) during
their life period. Stems of tender plants (and other organs) can be easily damaged by
strong wind, frost, pouring rain, insects, different animals due to poor handling, etc.
Thus, in the process of evolution, they develop an adaptive mechanism of protection
against damage, that is, the ability to recover. In some cases, natural damage (also a
severe one) can be a common and necessary stage of the development of an individual
(plants and animals), which results in breakage, and death of some parts [7]. The abil-
ity to repair can be considered as one of the adaptive modifi cations; it is proportionally
equal to intensity and duration of the effect of artifi cial and natural damaging factor.
Adaptive modifi cation takes place when intensity and duration of a damaging factor
is within the limit defi ned by previous evolution history of a species. Nonadaptive
changes, when a plant does not show adequate response and may die, can occur, pro-
vided intensity and duration of a damaging factor exceeds a standard [8].
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