DESCRIPTION OF EUROPEAN CHESTNUT
F. Ferrini and F.P. Nicese
Horticulture Department - University of Florence - Italy
BOTANICAL SPECIES: Castanea sativa Mill.
HABITAT. At present we still don’t know what was the actual area of the first diffusion of European Chestnut, even some Authors agree that we can indicate the Mediterranean Eurasian (Middle-East) as the original area where it is native from. In Europe, chestnut is generally grown between 300 and 800-900 m a.s.l., but we can also find good plants at the sea level and at an elevation more than 1000 m a.s.l. in Southern Italy, Greece and Spain. For the Euro-Japanese hybrids the limits are about 100-200 m lower.
Even though the European chestnut is a heliophilous plant, it likes N-NE exposures because they are less subjected to summer drought and they have more regularity in the seasonal changes overall between the end of the Winter and the beginning of the Spring.
Chestnut is generally grown in zones with more than 600 mm/year of rainfall. However much important is the frequency of the rainfalls in the summer.
The winter hardiness is good (up to -20 -25°C). As regards the annual mean, chestnut grows well in zones that have an annual mean temperature between 8 and 15°C, and at least with six months with mean higher than 10 °C
As to the soil is known the high relevance of pH value, that wouldn't be higher than 6, and of the active limestone, because of the high sensitivity of chestnut. However, it seems that such sensitivity is lower in soils with high potassium content and in zone with abundant rainfalls.
PLANT. The European chestnut or sweet chestnut (C. sativa) is a long-lived tree (400-500 years) with a majestic shape, 10-20 m tall (but some specimens can be 30-35 m in height) and with a trunk diameter between 60-70 cm and more than 2 m. The crown is spreading and roundish. The root system is sturdy and very expanded but not very deep. The stem is straight and often squat. After 20-25 years the bark begins to crack, originating a dark-reddish thick rhytidome (outer bark), with long and big protuberances sometimes spiral-shaped. In the younger shoots the bark is smooth, brilliant brown-red, which tends to become grey as the season progresses. On the younger shoots are visible typical white and roundish lenticels. Buds are smooth, short and squat with a dark-reddish color.
LEAVES. Leaves are apparently distich for the pedicel torsion, which is long between 1,5 and 2,5 cm. Leaf form are usually elliptic-lanceolate, with a coarsely toothed margin but it can vary from being wavy-edged (crenate), and with a acuminate apex; they are also very coriaceous, bright green and quite big (12-20 cm in length and 3-6 in width). The veining is very evident. All chestnut species are deciduous and the bud breaking is quite late in the season (usually it starts in early April but it can happen up to mid-may, depending on the climate condition, the species or the ecotype (the eurojapanese hybrid and the wild ecotype are more precocious), the altitude and the exposure of the orchard an so on. The vegetative cycle lasts 140-185 days.
FLOWERS. Chestnut species are, in general, monoeocious: on the same plant are present, in different position, male and female flowers. In general the male flowering precedes that of female flowers. The male flowers are grouped in the unisexual catkins located in the lower part of the shoot or, in the distal part of the shoot, in the bisexual catkins. Staminate flowers are spirally arranged along the axis of the catkins in cluster of three to seven The catkins are very "garish" (especially in the eurojapanese hybrids) and white to cream-coloured, very long (15-20 up to 30-35 cm). In general, only the wild ecotypes of European chestnut produce pollen.
Both type of catkins (unisexual or bisexual) are born in the current year’s growth and the position, the length and the habit (upright or hanging) are different depending on the cultivar. The male flowers can be distinguished in: sterile (with no stamina) and fertile (with stamina). Depending on the stamina length they can be classified in: astaminate, brachystaminate, mesostaminate and longistaminate. Only the flower which have stamina longer than 5-7 mm with well developed anthers are fertile.
The Spring climatic conditions can anticipate or postpone the bloom; however in general, the male flowers anthesis starts in early June but it can be much later depending on the cultivar and the environmental characteristics. Generally the anthesis lasts for 20-30 days: the male catkins bloom first. The female flowers are at the base of the bisexual catkins, and bear 1-5 flowers, but only 2-3 are fertile. Each of this inflorescences contains, on average, three female flowers that can produce 3 fruits
The major part of the "Marroni" cultivars are not self-fertile both because they don’t produce pollen (astaminate cultivars) or because the pollen is not able to pollinate the female flowers of the same cultivar (morphological and factorial sterility).
FRUIT. The fruit is botanically an achenium, commonly called chestnut, enclosed in a very thorny burr; the nuts are usually dark in color, pointed, and may have characteristic stripes running lengthwise. They vary in size, but nuts from most cultivars are rather large, ranging from 10 to 25 g. European chestnuts are less sweet than the American ones, and sometimes they can be astringent, and difficult to peel (to remove the pellicle-episperm) but many cultivars are exceptions to these generalities and can be very sweet and easy to peel. Fruit shape is determined, besides by the species and the cultivar, by the number of fruit/burr and the position inside the burr: it is emispherical for the lateral fruits, flattened for the central one. Quite often some empty chestnuts can be present.
CULTIVARS. Genetic diversity is very high for most traits, although differences among certain cultivars ("Marroni" for example) may be small, even tough separated by great distances according to isozyme studies. Some genotypes have easily removed pellicle while in other this is adherent. In general, the nuts are not very sweet and may even be astringent when uncooked. However, sweet non astringent types do exist. Therefore, germplasm reserves in Europe are large.
Cultivated forms include hundreds of named varieties selected for specific nut qualities and consumers uses such as: candying, roasting, boiling, drying, flour and domestic and export marketing. Certain clones have been selected for their superior timber form and wood quality and many dual purposes cultivars are known. From a nut quality standpoint, among the best and most well known are "Marroni". The word is subject of debate among producers, merchants and consumers, each of whom seems to have an idea about what a "Marrone" really is. The simplest definition may be that offered in France where a distinction is made between "chestnuts" and "Marroni" stating that while both are the fruit of the chestnut tree, the kernel is divided into multiple embryos (with pellicle intrusion) in chestnut while the "Marroni" are defined as particular cultivars of the best quality, well adapted to candying, with a small hylar scar that tends to be rectangular, a light coloured shell with dark, closely spaced stripes often in relief and the nutmeat is not grooved and is easily separated from the pellicle that does not intrude into the cotiledonary mass. Some Authors added that "Marroni" are formed either one or two per burr, the nut is never divided into more than one cotyledon, the flavour is sweeter and the tree has more exacting requirements and, in general, is less productive (number of chestnuts per single tree) than ordinary chestnut. Many of the "Marroni" cultivars are male sterile (they do not produce pollen and have astaminate or brachystaminate catkins). From a technical standpoint the cultivar are distinguished in: "Marroni" (Italian and French cultivar), Chestnuts and hybrids between European chestnut and the Asian species.
ITALIAN "MARRONI": the burr is very big, with a quadrangular shape. When the fruit are ripened the burr opens in 3-4 valves and contains 1-3 fruits. Only when pollination have been good, all three fruit are normal, more often, only 1-2 fruits are well developed and the other(s) is (are) deformed. The skin is brown with evident stripes. Fruit weight ranges from 10 to 25 g. The most widely grown are: "Marrone di Chiusa Pesio", "Marron Buono di Marradi", "Caprese Michelangelo", "Feltre", "Val Sugana", "Città di Castello", "Marrone di Palazzolo sul Senio", "Marrone di Firenzuola", "Marrone di Avellino", etc.
CHESTNUTS: several chestnut varieties that for the exterior characteristics of the fruits are very similar to the most famous "Marroni". Sometimes they are preferred by the growers for their higher rusticity and their productivity. From North to South we should mentioned the "Gioviasca", "Garrone" (rosso and nero), "Castagna della Madonna" or "Tempuriva", "Carpinese" (also called "Carrarese"), "Pistolese" and the "Raggiolana", "Castagna di Montella".
FRENCH "MARRONI": among the most widely grown varieties we should mentioned: "Sardonne"; "Comballe", "Bouche Rouge", "Marron d’Olargues", "Belle Epine", "Marron du Var". HYBRID CULTIVARS: the most widely grown are: "Marigoule, "Maraval", "Bournette", "Marsol", "Precoce Migoule", "Vignols", "Bouche de Betizac".
USES. Historically, the European chestnut (Castanea sativa) was important because it provided large quantities of sweet edible chestnuts to people, domestic animals and wildlife including deer and bear. An entire food chain was based on the abundant annual production of the chestnut forests. Often, pigs were allowed to forage for chestnuts in the fall. "Chestnut-fattened" pork was justly famous for its fine quality. At present most of the fruit production is for the fresh market and for dried chestnut (about 80% in Italy), livestock food (5-10%) and for confectionery (10-15%). Chestnut wood was used for building and roofing materials, fencing, mine timbers and railroad ties. Chestnut log cabins and split-rail fences can still be seen in some parts of the chestnut's former natural range. The wood and bark are rich in easily extracted tannins, much used by the leather tanning industry. The total volume of chestnut timber was probably more than that of any other tree species. However there are still thousands of hectares for pole production and for wood production.