Perhaps during nomadic life, the first food has been consumed by man, the chestnut dates to primitive times. The chestnuts (Castanea), members of the family Fagaceae, naturally occur throughout deciduous forests of eastern North America, Europe, and Asia. The genus Castanea comprises seven species. Four species are native to Asia: Chinese chestnut (Castanea mollissima Bl.), Seguin chestnut (Castanea seguinii Dode.), and Henry chestnut (Castanea henryi Rehd. & Wils.) on mainland China and Japanese chestnut (Castanea crenata Sieb. & Zucc.) on the Japanese islands and Korean peninsula. Two species are native to North America: the American chestnut (Castanea dentata) and chinkapin (Castanea pumila Mill.). European chestnut (Castanea sativa Mill.) is native to southern Europe and western Asia. All species are diploid (2n = 2X = 24) and hybridize freely, but interspecific F1’s usually suffer from low seed germination and male sterility. Blight resistance among the species differs. The American and the European species are susceptible, whereas the Asian species are blight resistant. The levels of susceptibility of the European and American species differ, and the American chestnut is the most susceptible species. Several recent studies on allozyme diversity suggest that the American chestnut has the lowest levels of genetic diversity among species in the genus (Huang, Norton, Boyhan, & Abraham, 1994). The American chestnut (Castanea dentata Marsh. Brokh) was once a dominant species in the eastern deciduous forest for 2000 year before chestnut blight (caused by Cryphonectria parasitica Murrill Barr) arrived on the North American continent near the turn of the century.
American chestnut trees (C. dentata) were once so common in the Eastern United States that everyone who could get to the woods in the fall could count on nuts for roasting and for stuffing their Thanksgiving turkey. The wood was highly resistant to rot, and used extensively for poles, fencing, and building materials. It was also of considerable economic importance, producing strong, rot-resistant timber, a source of tannins, fuel, wood, and nuts. Because of its utility, rapid growth, ability to quickly colonize burned or clear-cut areas, and edible nuts it has been referred to as the “perfect tree”. The pathogen of chestnut blight infects stem tissues and kills the above ground portions of trees by girdling them. Below ground the trees can survive for many years however, continuously sending up sprouts which are themselves eventually infected. Cryphonectria, which shows a necrotrophic life style is lesser studied than their biotrophic counterparts. Today, except for occasional trees near the edge of its range which have escaped the blight, American chestnut exists primarily as shrubs, sprouting from the stumps of blight-topped trees. Although to a lesser extent, European chestnut (C. sativa) was also devastated by introduction of C. parasitica. Despite their close relationship, sister species of Castanea exhibit very different susceptibilities to Cryphonectria infection. Asian chestnuts, the vector for the spread of Cryphonectria westward, range from somewhat susceptible to nearly immune to infection. Most likely, these species co-evolved with Cryphonectria. Slow growing cankers are often visible on Chinese and Japanese chestnut trees although growth and yield of the trees are not substantially reduced. European chestnut can tolerate infection slightly more than American chestnut.
Chestnut trees are of moderate growth rate (for the Chinese chestnut tree) to fast-growing for American and European species. Their mature heights vary from the smallest species of chinkapins, often shrubby, to the giant of past American forests, C. dentata that could reach 200 ft. Between these extremes are found the Japanese chestnut (C. crenata) at 33 ft. average; followed by the Chinese chestnut (C. mollissima) at about 50 ft., then the European chestnut (C. sativa) around 100 ft. (council, 2000). The Chinese and Japanese chestnuts are both often multilayered and wide-spreading, whereas European and especially American species incline to grow very erect comparatively, with little tapered, well established and massive columnar trunks with wide, rounded and dense canopy head at maturity. Its bark is smooth when young of a vinous maroon or red-brown color for the American chestnut, grey for the European chestnut (Detwiler, 1915). With age, American species’ bark becomes grey and darker, thick and deeply furrowed; the furrows run longitudinally, and tend to twist around the trunk as the tree ages like one of a large cable with twisted strands (Grieve M. M., 1900). The leaves are simple with acuminate leaf apex, obtuse leaf base, 12–25 cm long and 5–11 cm wide, with serrate margin shape and pointed and broadly spaced teeth, with rounded to angular type sinus shape.
After vegetation flowering stage appear in late spring or early summer until july. They are arranged in long catkins of two kinds, with both kinds being borne on every tree (Minnesota, 2008). Some catkins are made of only male flowers, which mature first. Each flower has eight stamens, or 10 to 12 for C. mollissima (Liao, 1976). The ripe pollen carries a heavy, sweet odor that some people find too sweet or unpleasant (Minnesota, 2008). Other catkins have these pollen-bearing flowers, but also carry near the twig from which these spring, small clusters of female or fruit-producing flowers. Two or three flowers together form a four-lobed prickly calybium, which ultimately grows completely together to make the brown hull, or husk, covering the fruits (Grieve M. M., 1900). Chestnut flowers are self-incompatible and they freely hybridize within Castanea species.
The fruit is contained in a spiny (very sharp) cupule 5–11 cm in diameter, also called “bur” or “burr” (VirginiaTech, 2008). The burrs are often paired or clustered on the branch and contain one to seven nuts according to the distinct species, varieties, and cultivars (Rushforth & Collins, 1999) (Bean & Murray, 1976). Around the time the fruits reach maturity, the burrs turn yellow-brown and split open in two or four sections. They can remain on the tree longer than they hold the fruit, but more often achieve complete opening and release the fruits only after having fallen on the ground; opening is partly due to soil humidity (Mencarelli, Postharvest Handling and Storage of Chestnuts, 2001). The chestnut fruit has a pointed end with a small tuft at its tip (called “flame” in Italian) (Mencarelli, Postharvest Handling and Storage of Chestnuts, 2001), and at the other end, a hilum – a pale brown attachment scar. In many varieties, the fruit is flattened on one or two sides. It has two skins. The first one is a hard, shiny, brown outer hull or husk, called the pericarps, the industry calls this the “peel”. Underneath the pericarps is another, thinner skin, called the pellicle or episperm (McLaren, 1999). The pellicle closely adheres to the seed itself, following the grooves usually present at the surface of the fruit. These grooves are of variable sizes and depths according to the species and variety. Inside the fruit there is fleshy and creamy two cotyledons but appears as one. Some varieties have only on large fruit per burr called as “marron” (Mencarelli, Postharvest Handling and Storage of Chestnuts., 2001). Fruit has no dormancy and can germinate right away after falling on ground, they can’t even store for long since they lose viability immediately so, they need to plant quickly.
Among all chestnut varieties European chestnuts are sweet in taste, easily removable skin and substantial size. American chestnuts are usually very small (around 5 g), but sweet-tasting with easy-to-remove pellicles. Some Japanese varieties have very large nuts (around 40 g), with typically difficult-to-remove pellicles. Chinese chestnut pellicles are usually easy to remove, and their sizes vary greatly according to the varieties, although usually smaller than the Japanese chestnut (council, 2000).
Evidence of chestnut cultivation by man is found since around 2000 BC. Alexander the Great and the Romans planted chestnut trees across Europe while on their various campaigns. A Greek army said to have survived their retreat from Asia Minor in 401–399 BC “thanks to their stores of chestnuts” (Filippone). Ancient Greeks, such as Dioscorides and Galen, wrote of chestnuts to comment on their medicinal properties and of the flatulence induced by eating too much of it to the early Christians, chestnuts symbolized chastity. In 1879 it was said that it almost exclusively fed whole populations of Italy for half the year, as “a temporary but complete substitution for cereals” (Play, 1879).
Palynological studies indicated that C. dentata was present in the southern Appalachian region 15000 year ago, and in the northern Appalachian region 5000 year ago and arrived in Connecticut 2000 year ago (Delcourt et al., 1980; Davis, 1981). Prior to blight, the native range of the American chestnut extended from southern Maine southward to Georgia, Alabama, and Mississippi and westward to southern Michigan, Indiana, and Tennessee. Every fourth tree in the central Appalachian forest was a chestnut (Saucier, 1973). This large, fast-growing tree played a significant role in forest ecosystems, providing food and habitat for a variety of wildlife. The reign of the American chestnut ended abruptly in the early 1900’s when a blight, caused by the fungus, Cryphonectria parasitica, was introduced to North America from Asia via infected chestnut nursery stock (Griffin, 2000). The blight was first observed in the Bronx Zoological Park in New York in 1904 (Roane, 1986) and within 50 years the American chestnut was nearly eliminated from the forest (Brewer, 1995). Only a few clumps of trees remained in Michigan, Wisconsin, California and the Pacific Northwest (Filippone). American chestnut can breed with Asiatic species to have blight resistance traits. Efforts started in the 1930s are still ongoing to repopulate the country with these trees in the United States. In the 1970s, geneticist Charles Burnham began back-breeding Asian chestnut into American chestnut populations to confer blight resistance with the minimum difference in genes (Cummer, 2003). In the 1950s, the Dunstan chestnut was developed in Greensboro, N.C., and constitutes most blight-free chestnuts produced in the United States annually.
Chestnuts depart from the norm for culinary nuts in that they have very little protein or fat, their calories coming chiefly from carbohydrates. Fresh chestnut fruits have about 180 kcal per 100 grams of edible parts, which is much lower than walnuts, almonds, other nuts and dried fruit (about 600 kcal/100 g). Chestnuts contain very little fat, mostly unsaturated, and no gluten (council, 2000). Their carbohydrate content compares with that of wheat and rice; chestnuts have twice as much starch as the potato on an as-is basis (Filippone). In addition, chestnuts contain about 8% of various sugars, mainly sucrose, glucose, fructose, and, in a lesser amount, stachyose and raffinose, which are fermented in the lower gut, producing gas (Mencarelli, Postharvest Handling and Storage of Chestnuts., 2001). In some areas, sweet chestnut trees are called “the bread tree”. When chestnuts are just starting to ripen, the fruit is mostly starch and is very firm under finger pressure from the high-water content. As the chestnuts ripen, the starch is slowly converted into sugars, and moisture content also starts decreasing. Upon pressing the chestnut, a slight ‘give’ can be felt; the hull is not so tense, and space occurs between it and the flesh of the fruit. They are the only “nuts” that contain vitamin C, with about 40 mg per 100 g of raw product, which is about 65% of the U.S. recommended daily intake. The amount of vitamin C decreases by about 40% after heating. Fresh chestnuts contain about 52% water by weight, which evaporates relatively quickly during storage; they can lose as much as 1% of weight in one day at 68 °F and 70% relative humidity (Mencarelli, Postharvest Handling and Storage of Chestnuts., 2001). Tannin is contained in the bark as well as in the wood, leaves, and seed husks. The husks contain 10–13% tannin (Rottsieper., 1946).
About 2,500 chestnut trees are growing on 60 acres near West Salem, Wisconsin, which is the world’s largest remaining stand of American chestnut.
The nut’s demand of chestnut surpasses supply in the country. The United States imported 4,056 metric tons of European in-shell chestnuts worth $10 million in 2007 (Geisler, 2008). The U.S. chestnut industry is in its infancy, producing less than 1% of total world production. Since the mid-20th century, most of the US imports are from Southern Italy, with the large, meaty, and richly flavored Sicilian chestnuts being considered among the best quality for bulk sale and supermarket retail. Some imports come from Portugal and France. The next two largest sources of imports are China and South Korea (Geisler, 2008).
A study of the sector in 2005 found that US producers are mainly part-timers diversifying an existing agricultural business, or hobbyists (University of Missouri, 2004). Another recent study indicates that investment in a new plantation takes 13 years to break even, at least within the current Australian market (McLaren, 1999). Starting a small-scale operation requires a relatively low initial investment; this is a factor in the small size of the present production operations, with half of them being within 3 to 10 acres. Another predetermining factor in the small productivity of the sector is that most orchards have been created less than 10 years ago, so have young trees which are as now barely entering commercial production. Assuming a 22 lbs. yield for a 10-year-old tree is a reliable conservative estimate, though some exceptional specimens of that age have yielded 220 lbs. So, most producers earn less than $5,000 per year, with a third of the total not having sold anything so far (University of Missouri, 2004). As of 2008, the price for chestnuts sold fresh in the shell ranges from $1.50 per pound wholesale to about $5 per pound retail, depending mainly on the size (University of Missouri, 2004).