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The fertilization of the chestnut tree
Since male catkins develop at the leaf nodes, blooming generally occurs very late in the second half of June and in early July.
The chestnut tree is an imperfect, monoecious plant; that is, its male and female flowers develop separately but on the same tree. Both types of flowers are situated on different parts of a new shoot.
At the bottom of the shoot, at the leaf nodes, terminal buds develop, which ultimately take over the roles of axillary buds, and become full-blown only whe the apical buds die off the following year. The 15-20 cm long and 1.5 cm thick male catkins develop at the leaf nodes in the middle of a shoot. At the top of the shoots, at the nodes of the smaller and narrower leaves, hermaphrodite catkins develop with female flowers situated at their bottoms and male flowers located in their middle and top parts. At the nodes of the shoot’s top leaves, buds - hiding new shoots - are being differentiated.
Our domestic conditions are suitable only for growing versions of the European chestnut species (Castanea sativa). In the rest of the chestnut producing countries, the species that are mostly grown are the Japanese chestnut (C. crenatá), the Chinese chestnut (C. mollissimá), and the American chestnut (C. dentata), along with certain selected - artificially and naturally pollinated - versions of these and other chestnut species, e.g. the Seguini chestnut (C. seguini) and the Allegany chestnut (C. pumild). Their flowering and fertilization are identical to those of the European chestnut, and the former only differ from the latter in their earlier flowering period, which actually would reduce the certainty of chestnut growing in Hungary. When they flower together, they are able to effectively fertilize the European chestnut species. Considering that we exclusively grow European chestnut species, we are interested only in their fertilization.
The conditions for pollination are primarily determined by the number of male flowers. The chestnut is mainly a wind-pollinated plant. To a lesser extent, insect-pollination is also possible: the male flowers produce both pollens and nectar, for which insects frequently visit them. Chestnut plantations and forests are especially valuable for beekeeper, because they provide bees with pasture after the end of the blooming period of acacia; in addition, pure chestnut honey has a high use and pleasure value.
The production of great amounts of pollens also indicate wind-pollination – in the anthers of the larger catkins’ male flowers there are more than 2000 pollens, and during their dispersion, there are enough pollens to pollinate the female flowers as far as 200-300 meters from the pollinating trees.
The male flowers of certain chestnut types may have congenital developmental disorders, which impede their pollen production. Nevertheless, among these breeds, there are several ingeniuos species with great growing and sales value, which can only be fertilized near trees that do produce pollens. Male flowers can have four types of developmental disorders:
  • Without stamen (astamineae): they grow regular-size catkins, but their flowers do not bloom or produce either anthers or pollens. The Italian species „Maroni” belongs to this group.
  • With disturbed stamen (brahistamineae): Unlike the previous breed, they grow a few short-stamen (1-3 mm) anthers, but they contain only a few, barely germinating pollens (Perella, Nerüw breeds).
  • With medium-length stamen (mesostamineae): They grow several short-stamen (3-5 mm) anthers, which contain enough germinating pollens (Pistolese type).
  • With long stamen (longistamineae): They grow a lot of well-developed, long-stamen (5-7 mm) anthers, which contain a great amount of germinating pollens.
The first two (the ones with reduced-value stamen) rarely occur in our domestic stands: all of our chestnut breeds develop stamens with adequate length.
The pollen production of our domestic chestnut types is good, the conditions for pollination are adequate, and the blooming trees serve as great bee pastures. An important condition for fertility is having adequate numbers of female flowers. Similar to walnut trees, chestnut trees are only able to grow female flowers on the shoots of the apical buds of young twigs. Growing large numbers of shoots are beneficial, because as the number of cupules per shoots increase, the market value of the produce decreases, the fruits remain tiny. In extreme cases, on the clustered varieties, no hermaphrodite catkins - only female catkins - develop. Such catkins become fertilized all the way to their tips, but their fruits are so tiny that they do not have any market value. It is characteristic of the typically large-fruit „Maroni” breeds to have only one flower fertilized and growing among the many flowers. On the well-producing and large fruit-size breeds, there are only two or three nuts per cupule. All of our cloned types belong to this group.
Certain breeds frequently grow twin sprouts. In these cases, there are not only more sprouts but also more seed leaves with accompanying inner hulls within their nuts. The ostensibly even, large seeds’ insides between the seed leaves are covered with hull webs to such an extent, that they significantly decrease their peelability.

Chestnut trees rely on mutual pollination. The tree’s different-sex flowers do not bloom at the same time. It is frequent that male flowers bloom earlier than female flowers. In case there is no outside fertilization, the male flowers, situated above the female flowers of the late-developing and blooming hermaphrodite catkins, are able to fertilize in 15-50% of the cases, which are only enough for below-average fruit production.

Unlike those of other fruit species, the sensitivity of the chestnut’s stigma cannot be determined, because there are neither excretions assisting pollen adherence, nor discoloration accompanying growth or ripening. Pollination research shows that the middle and side flowers are open to fertilization within 8-21 days of stigma development. Pollination taking place within eight days of the stigmas’ appearance are inefficient. For the sake of good productivity, it is expedient to plant several types of mutually pollinating trees in clone plantations. According to Solignat’s research, compared to the smaller fruit-size pollinating trees, the size of the fruits are greater by 13-20% due to the influence of large-fruit pollinating trees.

Source: Szentiványi, Péter, Dr. - Chestnut - Agricultural Publisher -
   
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