FREE BOOKS

Author's List




PREV.   NEXT  
|<   74   75   76   77   78   79   80   81   82   83   84   85   86   87   88   89   90   91   92   93   94   95   96   97   98  
99   100   101   102   103   104   105   106   107   108   109   110   111   112   113   114   115   116   117   118   119   120   121   122   123   >>   >|  
eared of all diseased trees. It is therefore possible that insect vectors or other agencies may have spread the disease to the scions of the topworked seedlings from the infected heartnut and butternut trees. Number 795 is the only _J. nigra_ tree on the station farm that has consistently shown symptoms of the disease during the past eight years, and in 1950 only a few limbs are affected. On the basis of the admittedly meager information reported here, it can be stated that the black walnut varieties used in these experiments are more resistant to the bunch disease than are varieties and seedlings of heartnut and butternut. That this is generally true is also borne out by the fact that in the vicinity of Beltsville, Maryland, and the District of Columbia, practically all dooryard trees of the Japanese walnut are infected with bunch disease, many of them having already been killed, whereas relatively few black walnut trees in the area show symptoms of the disease. The suggestion has been made that most varieties and seedlings of black walnut are symptomless carriers of the disease, and only under certain adverse conditions of environment would symptoms appear. This would explain why trees that are cut back severely, as was the case with tree Number 838 described above, show symptoms on the excessively vigorous shoots of the next year's growth. Little can be said at the present time about the relative resistance of black walnut varieties to the bunch disease because nothing is known about how it is spread from one individual tree to another. The case histories of trees described in the present paper are considered to be worth recording because they show that black walnut trees may support diseased scions and later regenerate apparently healthy tops. In these cases the trees showed a type of resistance to the disease. However, there are many cases known, the majority of which are seedlings, in which black walnut trees became so badly infected with the disease that nut production ceased and the trees later died. Whether the type of resistance described in this paper is widely prevalent in the black walnut as a species will be impossible to determine until more is known about how the disease is spread. FOOTNOTES: [Footnote 13: Several common names have been applied to this disease, among which "bunch" and "brooming" have most frequently been used. The authors strongly feel that the accepted common name should be "b
PREV.   NEXT  
|<   74   75   76   77   78   79   80   81   82   83   84   85   86   87   88   89   90   91   92   93   94   95   96   97   98  
99   100   101   102   103   104   105   106   107   108   109   110   111   112   113   114   115   116   117   118   119   120   121   122   123   >>   >|  



Top keywords:

disease

 

walnut

 

varieties

 
symptoms
 
seedlings
 

spread

 
resistance
 

infected

 

present

 

diseased


common
 

Number

 

heartnut

 

scions

 

butternut

 
strongly
 

authors

 

brooming

 

histories

 
individual

frequently

 
relative
 

shoots

 

vigorous

 

excessively

 

growth

 

Little

 
accepted
 

determine

 

impossible


Footnote

 

FOOTNOTES

 

Whether

 

widely

 

species

 

ceased

 

production

 

Several

 

regenerate

 

apparently


healthy

 

support

 

prevalent

 

recording

 

majority

 

However

 
showed
 

applied

 

considered

 

admittedly