diameter, white, hermaphroditic, and are attractive for pollinators [40]. The cherry
flower structure is usually characterized by stamina standing far from the pistil, thus
insects can touch the stigma only during nectar collection, passing along the pistil
[41]. In cherries like in most of the temperate fruit trees, sieve tubes more or less
directly supply secretory parenchyma cells called the “nectariferous tissue” with prenectar prior to nectar secretion. The nectary is receptacular, covering the whole
surface of the receptacle [42].
For the protogyn, sour cherry varieties is very important to know the periodicity
of nectar production and the synchronization of the endogen rhythm with stigma
receptivity and anther dehiscence. As it was stated in [43], dichogam flowers
produce nectar periodically by 12th hours, the homogam ones by 6th hours, and
the time of maximum production is synchronized by the stigma receptivity and
anther dehiscence. In the hybrids of sweet and sour cherries, 3-h gaps can be
observed in nectar production [43]. Additionally, the change of pollination strategy
for the protogyn sour varieties: (i) stigma exerted – wind pollination, (ii) state of
pollination chamber – beetle pollination, (iii) opening of anthers – pollination by
bees and other insects was observed [44].
A sour cherry flower may secrete nectar for 2–4 days and, depending on the
cultivar, produces 0.2–9.0 mg nectar. Generally, autochthonous landraces like
“Cigánymeggy” or “Oblačinska sour cherry” type yield less but more concentrated
nectar, with sugar values of 0.1–1.8 mg/flower/day, while cultivated varieties produce more but rather dilute nectar [45]. Among sour cherry cultivars, “Meteor korai”
and “Debreceni bötermö” are one of the best nectar producers giving 10.27 μl and
7.21 μl of nectar respectively; with 13.96% and 16.6% of sugar, respectively [46].
The nectar of early blooming fruit trees such are cherries is important for
honeybees in the brood rearing season, but rarely can provide unifloral honey, as
well [45]. Sweet cherry blossom is more attractive for bees than sour cherry
blossoms primarily because the nectar of sweet cherries is much richer in sugar
(55%) than that of sour cherries (28%). But, sour cherry cultivars produce
a significant amount of nectar at night [47], thus attracting night insects.
If a successful fertilization should be achieved even at self-incompatible cherry
and sour cherry cultivars, all details of their pollination biology should be known,
including the sugar and polyphenolic composition of nectar, as ones of the primary
attractants [46, 48].
4
Nectar Compositions
The number of papers related to the examination of the chemical composition of the
floral nectar is not large, although it is much more available for floral nectars than for
extrafloral nectars. Mainly studies have focused on the qualitative aspect. The main
components of the nectar, sugars and amino acids, were the most examined, while
other solutes were not subjected to the research to that extent. This is rationale since
the nectar is predominantly an aqueous solution of sugars. Also, sampling is not easy
considering the duration of secretion (few hours to several days), and the amount of
29 Sugar and Polyphenolic Diversity in Floral Nectar of Cherry
759
flower structure is usually characterized by stamina standing far from the pistil, thus
insects can touch the stigma only during nectar collection, passing along the pistil
[41]. In cherries like in most of the temperate fruit trees, sieve tubes more or less
directly supply secretory parenchyma cells called the “nectariferous tissue” with prenectar prior to nectar secretion. The nectary is receptacular, covering the whole
surface of the receptacle [42].
For the protogyn, sour cherry varieties is very important to know the periodicity
of nectar production and the synchronization of the endogen rhythm with stigma
receptivity and anther dehiscence. As it was stated in [43], dichogam flowers
produce nectar periodically by 12th hours, the homogam ones by 6th hours, and
the time of maximum production is synchronized by the stigma receptivity and
anther dehiscence. In the hybrids of sweet and sour cherries, 3-h gaps can be
observed in nectar production [43]. Additionally, the change of pollination strategy
for the protogyn sour varieties: (i) stigma exerted – wind pollination, (ii) state of
pollination chamber – beetle pollination, (iii) opening of anthers – pollination by
bees and other insects was observed [44].
A sour cherry flower may secrete nectar for 2–4 days and, depending on the
cultivar, produces 0.2–9.0 mg nectar. Generally, autochthonous landraces like
“Cigánymeggy” or “Oblačinska sour cherry” type yield less but more concentrated
nectar, with sugar values of 0.1–1.8 mg/flower/day, while cultivated varieties produce more but rather dilute nectar [45]. Among sour cherry cultivars, “Meteor korai”
and “Debreceni bötermö” are one of the best nectar producers giving 10.27 μl and
7.21 μl of nectar respectively; with 13.96% and 16.6% of sugar, respectively [46].
The nectar of early blooming fruit trees such are cherries is important for
honeybees in the brood rearing season, but rarely can provide unifloral honey, as
well [45]. Sweet cherry blossom is more attractive for bees than sour cherry
blossoms primarily because the nectar of sweet cherries is much richer in sugar
(55%) than that of sour cherries (28%). But, sour cherry cultivars produce
a significant amount of nectar at night [47], thus attracting night insects.
If a successful fertilization should be achieved even at self-incompatible cherry
and sour cherry cultivars, all details of their pollination biology should be known,
including the sugar and polyphenolic composition of nectar, as ones of the primary
attractants [46, 48].
4
Nectar Compositions
The number of papers related to the examination of the chemical composition of the
floral nectar is not large, although it is much more available for floral nectars than for
extrafloral nectars. Mainly studies have focused on the qualitative aspect. The main
components of the nectar, sugars and amino acids, were the most examined, while
other solutes were not subjected to the research to that extent. This is rationale since
the nectar is predominantly an aqueous solution of sugars. Also, sampling is not easy
considering the duration of secretion (few hours to several days), and the amount of
29 Sugar and Polyphenolic Diversity in Floral Nectar of Cherry
759