184 PYTHIUM DISEASE OF GINGER, TOBACCO AND PAPAYA 



coated with a black crust, covering up the dried fibrous tissue below. This 

 black crust is composed of the dead plant tissues coloured by the mycelium of 

 a Diplodia. The disease is usually active only during the monsoon months, 

 but may then develop with such rapidity as to make considerable progress 

 before the gardener is aware of its presence. It is found chiefly at the base of 

 the trees near the ground-level, but in rare cases it may also occur on the trunk 

 higher up. The disease is most common on trees two or three years old and 

 is rare on young ones. If the attack is very late in the rainy season the trees 

 recover soon ; the diseased patch is heaied up and the bark only is cast ofi. 

 Even in extremely severe attacks the tree is not killed rapidly. The efiect is 

 often confined for a long time to lessening the yield and size of the fruits. 

 During stormy weather many trees fall over, breaking away at the point of 

 attack. Cultures taken from the coal black crust commonly found in all 

 diseased patches gave almost invariably a fungus belonging to the genus 

 Diplodia, which has been identified with some doubt as Diplodia PapaycE 

 Thuemi. For some time this fungus was supposed to be the causative 

 organism. Inoculation experiments, however, did not produce the disease 

 artificially under any circumstances. 



In 1914, a Pythium belonging to the gracile group was isolated from the 

 diseased papaya trees, and inoculations with this species did not yield any 

 results. The inoculations were done in the cold weather, and the failure of 

 these may be explained, in the light of the present experiments, as being due 

 to the low temperature and dry weather at the time. 



Recently an old tree was found with the typical symptoms of the disease. 

 Many saprophytic fungi and bacteria were found in the diseased patches. 

 Sections from the portion between the healthy and diseased patches revealed 

 the presence of the mycelium of a Phycomycetous fungus in the tissues, and 

 the same kind of mycelium was found under the bark and throughout the 

 diseased patch ramifying freely through the cells. In one place there was a 

 good fluffy growth. The mycelium was hyaline, with thick, granular pro- 

 toplasm, unseptate in the young hyphse and irregularly septate in the older. 

 Pure cultures from this mycelium grown on glucose agar proved it to be a 

 species of Pythium belonging to the gracile group and quite identical with that 

 found on tobacco and ginger. The mycelium in the diseased bark disappears 

 very soon and it is very difiicult to detect it in old diseased patches. This 

 explains the failure to find it in the earlier investigations. 



1 Sydow, H. and P., and Butler, E. J. " Fungi ludiae Orientales, Part V. " Ann. Mycol., 

 XIV, 1916, p. 198. 



