Chestnuts | Article | Woodworking

Chestnuts

Name referring to seven species of deciduous, nut-bearing trees found native and introduced throughout the world (Table 1). The nuts are actually fruits, with the shells enclosing cotyledons. Trees bear both male and female flowers in late spring, but must be cross pollinated for nut production. Nuts are born in a spiny involucre or bur which opens to release the nuts in late fall.

Japanese chestnuts (Castanea crenata) and Chinese chestnuts (C. mollissima) are grown in Asia and the United States for their nuts, and many cultivars have been selected. European chestnuts (C. sativa) were distributed throughout southern Europe from the Caucasus mountains, where they are native, and the nuts have become an important food source, both cooked whole and ground into flour. American chestnuts (C. dentata) have smaller nuts than Asian or European species, but they are usually sweeter. Only American trees served as an important source of lumber, due to length of their unbranched trunks. All species have been used as a source of tannin for the leather-tanning industry. American and Chinese chinquapins (C. pumila and C. henryi) have very small nuts that are an important source of food for wildlife. Americans have imported and planted all foreign species of Castanea, starting with Thomas Jefferson (C. sativa, 1773), and continuing to the present (C. crenata, 1876; C. mollissima, 1903; C. henryi, 1908; C. seguinii, 1918). All of the species can be crossed, and hybrids have been selected primarily as orchard cultivars.

Limiting Factors

In 1838 a root disease was reported on European chestnut in Portugal, and soon after this "ink disease" was found in several other parts of southern Europe. The pathogen, Phytophthora cinnamomi, causes brownish-black lesions on the roots that exude an inky-blue stain. Lesions expand, coalesce, and girdle the root. Trees are killed when the root collar is girdled, or when most of the roots are killed. Breeding with resistant Asian species has produced new cultivars, and careful sanitation and site selection allow European chestnuts to still be grown. Ink disease probably accounted for the recession of chestnut from large areas in the Gulf and Atlantic states in the United States, and inland to the foothills and mountains of Mississippi, Alabama, Georgia, Tennessee, Maryland, Virginia, and the Carolinas. The fungus is assumed to have entered the United States in the mid-1800's.

The second disaster for American and European chestnuts was also a fungus disease. Cryphonectria (formerly Endothia) parasitica was first reported in New York City in 1904, and found to be wide spread in the North Eastern U.S. Chestnut blight had probably entered the U.S. on imported Japanese chestnuts in the late 1800's. Initial spread was on nursery stock (most major mail-order nurseries sold Japanese chestnuts at the turn of the century), but spores were also carried on the fur, feet, and feathers of all the birds, animals and insects that walked up and down the trees. Wounds in the bark allow access and initial fungal growth, and the resulting canker expands to kill the cambium and eventually girdles the twig, branch, or trunk. The fungus does not kill the root collar, and the dormant embryos there sprout and grow until wounded, infected and killed and the cycle is repeated. In the northern part of the natural range of American chestnut (Northern Georgia to Southern Maine, and west through Ohio, Kentucky, and Tennessee), sprout-clumps have survived well, but further south repeated chestnut blight cycles kills the sprout clumps. American chinquapins are also very susceptible to chestnut blight, and their sprouting system (relying on the old root system, instead of forming new roots as chestnut does) may make them more liable to be totally killed by blight.

Chestnut blight was first reported in Europe on chestnuts in Italy in 1938. The epidemic there proceeded as in the U.S., but natural virus infection of the fungus has now provided a biological control. The fungal strains with viruses are less virulent (thus "hypovirulent"), and can be inoculated into natural cankers to transmit the viruses and establish biological control in orchards. Hypovirulent strains have been used in the U.S. for control of blight fungus populations in orchards and forest stands of American chestnut sprouts. Improved control may result from new strains developed at the Roche Institute in New Jersey that have cDNA copies of the viral dsRNA genome inserted into the DNA of the chestnut blight fungus. In addition, breeding of trees for resistance has been in progress for many years crossing susceptible trees with resistant Chinese and Japanese chestnuts, and orchard and timber types with chestnut blight resistance should soon be available.

The next potential disaster for chestnut trees in the U.S. and Europe is infestation with a small wasp, native to Asia, called the Oriental Chestnut Gall Wasp (Dryocosmus kuriphilus). Eggs laid in leaf and flower buds develop into galls, and heavy infestations can kill the trees. The insect has been in the U.S. since 1974 (on Chinese chestnut trees in orchards in Georgia), and is now on American chestnut trees at the Southern part of the range. There are no reports of this insect in Europe, as yet. Japanese chestnut breeders have released cultivars with some resistance to the insect, and American chinquapins seem to have good resistance. Clearly, this must be considered in future breeding plans.

Future Prospects

Improved biocontrol of chestnut blight based on natural and engineered introduction of hypovirulence viruses, and improved resistance by tree breeding can allow chestnuts to be useful in the U.S. A control for ink disease is still needed, but tree breeding can also help eliminate this threat. World-wide cooperation to study, and prevent damage by gall wasp can allow chestnuts to be useful as orchard and timber trees around the world.

**Table 1. Species of Chestnut**
THREE NUTS PER BUR
Castanea dentata (Marshall) Borkhausen	American chestnut
Castanea sativa Miller	European chestnut
Castanea crenata Siebold and Zuccarini	Japanese chestnut
Castanea mollissima Blume	Chinese chestnut
Castanea seguinii Dode	Dwarf Chinese chestnut
ONE NUT PER BUR
Castanea henryi (Skan) Rehder and Wilson	Chinese chinquapin
Castanea pumila (Linnaeus) Miller	American chinquapin
var. pumila	Allegheny chinquapin
var. ozarkensis (Ashe) Tucker	Ozark chinquapin

Return to "The Chestnut Story" Introduction

Chestnuts

An Historical Reference for Chestnut Introductions Into North America

Chestnuts And The Introduction Of Chestnut Blight

Oriental Chestnut Gall Wasp Found On American Chestnut Trees

Valuable Chestnut Germplasm In Connecticut

Chestnut Breeding In The United States

Sources Of Chestnut Trees 1998

For more information contact Sandra L. Anagnostakis, The Connecticut Agricultural Experiment Station, Box 1106, New Haven, CT 06504, phone 203-974-8498, fax 203-974-8502.