46 



THE AGRICULTURAL NEWS. 



February 3, 1912. 



FUNGUS NOTES. 



SOFT ROT OF' GINGER IN BENGAL. 



This disease atifords a useful example of the damage that 

 may be inflicted by a soil saprophyte when it is able to func- 

 tion as a facultative parasite upon the underground portions of 

 living plants; at the same time, the account of its usual source 

 of origin and general effects shows how practical and purely 

 empirical methods of cultivation of a crop may be profoundly 

 influenced by the presence of a disease, of unknown cause, 

 whose proper treatment has not been fully elucidated. The 

 information concerning this disease is taken from an article 

 in the A;/riculfu,'til Jiiuriifd of India, Vol. VI, Part II, by 

 \V. McRae, MA.,B.Sc, Supernumerary Mycologist to the 

 Government of India. 



The soil most suitable for the cultivation of ginger is 

 a light sandy loam or a well drained loam. Usually, ground 

 is chosen that has remained fallow for three years or more, 

 and is in consequence generally over-run by grass. When the 

 crop has been harvested, the field is not again planted in 

 ginger for a period varying from three to ten years, five years 

 being a common time. This long interval is said to be necessary 

 because the crop makes heavy demands on the food content 

 of the soil, and because it is liable to a disease when planted 

 more frequently in the same spot. Unoccupied land is 

 plentiful in that part of Bengal where ginger is grown, so 

 that there is no need for the rotation which other conditions 

 would render imperative. 



In preparing it for this crop, the land is reduced to a very 

 fine state of tilth and a most efficient system of drainage is 

 employed, to prevent the accumulation of stagnant water, 

 since good drainage is one of the most essential requisites. 

 The 'seed' is planted out in March and by the middle of 

 August or September, the plants are about li feet high. 

 Then a disease attacks them, and causes the leaves to turn 

 yellow. Good cultivators recognize this disease and its in- 

 fectious nature, and pull up the yellow-leaved plants and 

 throw them into an out of-the way corner. Removal con- 

 tinues until the end of Septemlier, after which time the 

 diseased plants are allowed to grow until late in Novem- 

 ber when they become partially mature. They are then 

 harvested and sold as spoiled ginger. The main, healthy, 

 portion of the crop is not taken up until .January or 

 February. 



'T'he first outward indication of the disease in the 

 growing crop is a general but slight paleness of the leaves 

 of a shoot, then the tips of the leaves turn yellow 

 and. this yellowing gradually spreads along the leaf to- 

 wards the leaf-sheath, often more rapidly along the 

 margins. Then the leaf tissue dies and becomes scar- 

 ious from the tip, the dead area gradually extending 

 towards the leaf sheath, following in the wake of the yellow- 

 discoloration. The leaves droop and hang down along the 

 stem, till finally the whole shoot becomes dry and withered. 

 Meanwhile the collar, that part of the aerial stem between 

 the place where it arises from the rhizome and where it 

 emerges from the ground, becomes of a pale, translucent 

 brown colour, and, by the time the leaves are well yellowed, 

 it is vt ry watery and soft, so that the whole shoot can easily 

 be lifted off, breaking away at this point, though not falling 

 over spontaneously. This soft rot also e.\tends beyond the 

 collar into the rhizome. The rotting is accelerated by the 

 combined action of other fungi, and of small eel-worms and 



the larvae of flies, which act as secondary agents. Both the 

 discoloration and .softening extend to the whole rhizome, 

 which gradually rots and disintegrates, forming a loose watery 

 mass of putrefying tissue, enclosed by the tough rind. The 

 vascular strands lie isolated inside. The roots attached to 

 the affected parts also present the same symptoms.' 



The disease is attributed to a fungus, Pythiuvi grncile, 

 found by Butler on ginger, in the Bombay Presidency, in 1902, 

 and also by McRae in Bengal in the case under consideration. 

 This forms zoosporangia on the outer surface of the substance 

 on which it lives, and oospores inside the substratum. The 

 latter arise from the fusion ef the contents of a male organ, 

 or antheridium, with those of a spherical female organ, known 

 as an oogonium. The fungus has been found to attack certain 

 green algae in Europe, and is also known to live as a sapro- 

 phyte on decaying humus in the .soil. Both Butler and McRae 

 found that eehvorms were also present on diseased rhizomes 

 of ginger, in many cases; but in early stages of the disease the 

 fungus alone occurred. No inoculation experiments have 

 been conducted, but in view of the regular occurrence of 

 Pythium gracile alone in early stages of the disease, there can 

 be little room for doubt that it is the cause. 



In many cases, dissection of the plant shows that infec- 

 tion has come from the ]ilant sets, and this seems to be the 

 method whereby the disease is usually introduced into the 

 growing crop. In some cases young buds below the ground, 

 or just above the surface, were found to be diseased, the 

 infected portion extending only for a very short distance. 

 A connexion was also traced between an affected shoot and 

 an adjacent bud below ground, that had been destroyed by 

 the disease. 



' It may be noted that the disease appears with the 

 advent of the rains and becomes epidemic only when the 

 rains have fairly well set in and the ground is wet. In damp 

 fields where the soil is stiff and retains water the attack is 

 always more severe, while on sandy loam the disease does not 

 usually reach an epidemic stage. When the rainy season is 

 about at a close, the removal of diseased plants (by the culti- 

 vators) ceases and any later attacked plants are allowed to 

 remain in the ground to do what they can before being finally 

 taken up and sold as inferior quality ginger. The cultivator 

 has learned by experience that, after the rainy season is over, 

 there is little tear of the di-sea-^e spreading much.' It may be 

 noted that this habit of leaving infected plants in the field, 

 and that of pulling off the tops of diseased plants earlier in 

 the season without taking steps to remove all the infected 

 rhizome as well, must be largely responsible for the general 

 occurrence of the disease in the district and for the necessity 

 of allowing the land to lie fallow for so long a period between 

 successive crops. 



Experiment plots of ginger planted with four v.uieties 

 obtained from .Jamaica, Cochin, Calicut and Bengal have 

 been maintained annually since 190-5-6 at the Kxperimental 

 Farm near Rangpur. No ginger is grown in the injmediate 

 neighbourhood. In 1907 all the plots were badly attacked 

 by disease, but subsequent methods of treatment have suc- 

 ceeded in eradicating it almost entirely, in that situation. 

 The remedial measures suggested for the general control of 

 the disease resulting from the experiments mentioned are as 

 follows : — 



' 1. On harvesting the crop all the rhizomes should be 

 removed from the ground, liiseased ones ought never to be 

 left on the ground. Thej* should ba collected with as many of 

 the roots attached as possible and burned or buried deeply in 

 a place where ginger is not grown. The shoots of diseased 

 plants should also be gathered and burned. 



