gQ4 The Philippine Journal of Science ms 



The Wase Unshiu variety is also planted commercially at 

 Ocho, Hiroshima Ken. The disease was observed at this place 

 also, although at the time of the observation most of the fruits 

 were harvested and no estimate of the injury due to the disease 

 could be made. The disease was said to have been first seen 

 two years before and at that time was very serious ; during the 

 present year (1919) it was not so injurious. 



DESCRIPTION OF THE DISEASE 



The disease has so far been observed only upon the Wase 

 Unshiu variety in the field ; it has not yet been observed occur- 

 ring naturally upon any of the other varieties of the Unshiu 

 oranges or upon any of the other Citrus species. The disease 

 is very peculiar in this respect in that in nature in Japan it 

 seems to be limited to a single horticultural variety, while closely 

 related varieties are not at all affected. 



The disease has so far been observed affecting only the fruits. 

 The skin of the fruit becomes a brown color ; the spot spreads 

 quickly, the center of the spot becoming lighter and grayish in 

 color, while the advancing edges of the spot remain dark brown 

 or even become dead black. The spot is slightly depressed and 

 a very definite line of demarcation exists between the diseased 

 spot and the normal skin. The size and the shape of the spots 

 vary; a spot may be as small as 2 to 3 millimeters in extent 

 in its longest diameter while the largest spot observed was 50 

 millimeters in its longest diameter. The longest diameter is 

 typically in a lateral direction as shown in Plate 1. As the 

 disease advances small black pustules can be seen forming in 

 large numbers in the grayish center of the lesion ; these are the 

 acervuli of the causal fungus and contain the spores of the 

 fungus in large numbers. The spots appear typically near the 

 blossom end of the fruit, usually just to one side of the navel, 

 never at the navel. The spots have never been observed as yet 

 to occur near the stem end of the fruit. 



The injury to the fruits is at first confined largely to the 

 skin and does not extend into the flesh of the fruit. In the 

 early stages of the disease, therefore, although the skin may be 

 blackened, giving to the fruit the appearance of being badly 

 rotted, it will nevertheless be intact within and perfectly edible. 

 With the advance of the disease, other fungi intrude which 

 spread into the flesh of the fruit more readily, and the fruit 

 becomes spoiled for use and quickly rots. The fruits, more- 

 over, when once affected, quickly drop to the ground and there 



