DANGEROUS FOREST DISEASES IN JAPAN 



ROKUYA IMAZEKI 



Director, Division of Forest Protection, Government Forest 

 Experiment Station, Meguro, Tokyo, Japan, and 



Kazuo Ito 



Chief, Section of Forest Pathology, Division of Forest Protection, 

 Government Forest Experiment Station, Tokyo, Japan, 



Witches'-Broom of Paulownia 



Virus (no specific name). In the case of normal paulownia, a bud 

 sprouts in spring and grows to a new stem or a new branch, which 

 bears about 10 pairs of opposite leaves. Stem growth ceases before the 

 beginning of September. The axillary buds of the new stem or the 

 branch do not sprout for this season, so that they usually have no 

 lateral shoots for the current season. In the diseased paulownia, on 

 the contrary, a bud sprouts in spring and grows to a new stem or to 

 a new branch which does not cease its growth until late in autumn and 

 the primary axillary buds sprout immediately. The sprouting of the 

 axillary buds and the growth of the shoots and branches without any 

 restriction are the causes of the symptom of the witehes'-broom. The 

 branches and shoots of the diseased tree are slender and brittle and 

 show an extreme negative geotropism. The color of diseased branches 

 and shoots becomes yellowish green. 



There are two sorts of leaf-forms in healthy paulownia, The one 

 is the leaf -form seen in young trees 1 or 2 years old and the other is 

 that seen in older trees. The former show both large and small in- 

 cisions. With the growth of the tree, the leaves which have only large 

 incisions increase in number, and within 2 or 3 years the whole tree 

 comes to have leaves with large incisions on the margin. In the 

 diseased tree, however, the leaves with both large and small incisions 

 appear even though it becomes more than 2 years old. Usually all 

 the leaves on the diseased shoots are abnormally thin and narrow, and 

 are uneven on the surface. Their color is yellowish. Malformed leaves 

 are often observed on the diseased shoots. 



This is the most serious disease of paulownia trees in Japan, and 

 causes severe damage in many plantations in the central and southern 

 parts of this country. Heavily infected trees are stunted and killed. 

 Insect transmission of this disease is not known. 



Intercontinental spread is possible through shipment of infected 

 trees or rootings. Importation of living plant material other than 

 pollen or seed should be forbidden. 



Distribution: In Japan it is common from the central to southern part 

 and scattered in the northern parts except Hokkaido. Also found 

 in China ; Korea ( ? ) . 

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