. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 406 GENETICS IN RELATION TO AGRICULTURE parasitica. The parasite is a native of eastern Asia where it is parasitic upon native species of chestnut, to which it appears to do relatively Uttle harm. In other words these species are highly resistant to the parasite. However, when the fungus was introduced into America, pre- sumably in nursery stock some 25 years ago, it found in our native species, Castanea americana, a very susceptible host (Fig. ). The parasite has already caused the destruction
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 406 GENETICS IN RELATION TO AGRICULTURE parasitica. The parasite is a native of eastern Asia where it is parasitic upon native species of chestnut, to which it appears to do relatively Uttle harm. In other words these species are highly resistant to the parasite. However, when the fungus was introduced into America, pre- sumably in nursery stock some 25 years ago, it found in our native species, Castanea americana, a very susceptible host (Fig. ). The parasite has already caused the destruction of the American species throughout the northern Appalachian region and is strongly threatening its complete extinction as a timber tree. Investigations have determined that the Euro-. FiG. 165.—An advanced stage of the chestnut bark disease, caused by Endothia parasitica, a virulent pathogenic fungus from China. {From the Journal of Heredity.) pean chestnut is also susceptible to the attacks of this fungus, so that the future existence of this species is also jeopardized. The American chest- nut is one of our most valuable forest trees and its destruction will entail an enormous loss. A very promising Chinese species is known pro- visionally as C. moUissima. While it is scarcely a timber tree as compared with our native species, yet it may thrive in our climate. As the nuts are of good quality and the tree has shown marked resistance to experi- mental inoculations on plants already established in this country it is hoped that it wiU prove to be a successful substitute for the vanishing American species. Even the culture of the American' species for com- mercial nut production in western North America will be constantly threatened. Hence it is fortunate that breeding experiments with the Digitized by Microsoft®. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illus
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