166 PLANT DISEASES 



MULBERRY ROOT DISEASE 



{Helicobasidium mompa, Tanaka.) 



Nobujiro Tanaka has described a disease of the mulberry 

 tree, which is extensively cultivated in Japan for rearing 

 silkworms. < The fungus first attacks the root of the living 

 tree, and after about two months, above-ground symptoms 

 are evident, the growth of shoots is arrested, and the 

 leaves become gradually smaller, and at length die; the 

 shoots also die as the disease advances. The lowest roots 

 are killed first, and the tree pushes out others higher up, 

 which in turn are destroyed, the tree sometimes keeping 

 itself alive for three years by the successive formation of 

 new roots. The diseased roots are covered with an 

 irregular network of purplish-brown strands of mycelium 

 0*5- 1 mm. thick; some of these radiate into the soil. As 

 the disease proceeds, the fungus creeps above ground, 

 forming at first a thin effused mass of mycelium of a dark 

 purple-brown colour, which more or less covers the base 

 of the stem and branches ; the surface of this felty mass is 

 smooth and velvety, and the definite margin paler in 

 colour. Extraneous matter, as dead leaves, branches, soil, 

 etc., are often enclosed in the rapidly spreading felt. As 

 growth proceeds, a portion usually develops at right angles 

 to the branch, and also extends laterally on one or both 

 sides. The hymenium is produced on every portion of 

 the free surface of the felt, and is whitish, with a tinge 

 of violet. The basidia are curved, 1-3 septate, four- 

 spored. 



Numerous sclerotia are formed in the decaying tissues 

 of dead roots. No remedial measures are given, but the 



