Albert Howard 375 



The wilt-disease of Java indigo and other monsoon crops. These wilt- 

 diseases are examples of a definite disease in which parasites have not 

 yet been shown to play a part. 



Java indigo (Indigofera arrecta Hochst.), the species now generally 

 cultivated in Bihar, frequently suffers from wilt during the late rains. 

 At the beginning of the monsoon, growth is normal but in wet years 

 a change takes place about mid-July in the character of the foliage while 

 the rate of growth slows down. The leaves alter in appearance, assume a 

 yellowish-green, slaty colour, become reduced in size and show extensive 

 longitudinal folding. After this, leaf fall is rapid until only stunted tufts 

 of foliage at the ends of the branches remain. In severe cases, this is 

 followed by the death of the plant, the process taking place slowly, a 

 branch at a time. The externa] symptoms of wilt suggest extensive root 

 damage which is confirmed by exposing the root-system by means of a 

 Knapsack sprayer. Wilted plants are found to possess very few fine roots 

 and nodules in an active condition. The main tap-root and the laterals 

 are alive and normal but the fine roots are mostly dead or discoloured 

 and the number of absorbing root hairs is exceedingly small. The de- 

 struction of the active root-system including the nodules takes place 

 from below upwards. When wilt is well established, the absorbing roots 

 still alive are all in the upper two or three inches of soil. Evidently some 

 factor is in operation which destroys the fine roots in the subsoil and 

 which afterwards affects those towards the surface. 



Other investigators have failed to find any parasite responsible for 

 the trouble. No insects could be discovered attacking the fine roots and 

 none of the well-marked appearances of fungoid attack were evident. 



The association of extensive root damage with wilt suggested a de- 

 tailed study of the roots. For this purpose, it was necessary to expose 

 the root-system without damage including the absorbing areas and the 

 nodules. This is easily accomplished in the fine silt-like soils of Bihar by 

 means of a Knapsack sprayer. The range in the root-systems of the 

 various types which make up the indigo crop was found to be as great 

 as that of the above-ground portion of the plant. The mode of branching 

 of the roots closely corresponded with that of the shoot. The type of 

 rooting could always therefore be foretold from the mode of branching. 

 The root-system in this crop is the mirror image of the shoot. Nodular 

 development was found to be most intense at the break of the rains in 

 May and June and to be most pronounced on the roots near the surface. 

 Soil-temperature was found to affect the growth of roots and a distinct 

 resting period ensued during the cold weather of December, January and 



