INSTITUTE, PUSA, FOR 1918-19 69 



IV. Diseases of plants. 



(1) Ufra of rice. An account of the investigations on 

 this disease carried out since the Bulletin published in 1913 

 was issued as a Memoir early in 1919. This contains a 

 further study of the life-history and activities of the rice 

 worm, Tylenchus angustus; an attempt to explain the ano- 

 malies in the behaviour of different classes of cultivated 

 paddies to the disease, which were noticed in the earlier 

 paper but which remained a complete puzzle until the close 

 relation between atmospheric humidity and the movements 

 of the worm on a dry surface was discovered ; and finally 

 the application of the facts ascertained to the control of 

 the disease. Further work is in progress or contemplated 

 regarding the factors which influence the motility of the 

 worm and those which influence its persistence under field 

 conditions from one season to the next. 



(2) Black Band disease of jute. The research work 

 on this disease was continued by Dr. Shaw during the year 

 under review. The amount of disease in the Bihar jute 

 crop was considerably less in 1918 than in the previous 

 year. This was very possibly due to the earlier termina- 

 tion of the monsoon, and the consequent exceptional dryness 

 during September, resulting in the jute seed crop being 

 harvested a month earlier than in 1917. On the Pusa 

 Farm, while the incidence of the disease was slight in the 

 main area of the crop, one small field was very badly in- 

 fected. This particular area had been under jute in 1916. 

 Whether the intensity of the disease in a crop is in any way 

 bound up with the length of rotation practised is a factor 

 which must be considered in future field experiments. The 

 fact, mentioned in the last report, that the late sown crop 

 appears to be relatively immune was abundantly confirmed 

 from the inspection of the jute crop all over Bihar. Statis- 

 tics obtained from the diseased portion of the crop on Pusa 

 Farm showed that it is only stems of a certain size and 

 maturity which are liable to infection under natural 

 conditions in the field. Thus of stems over 5 feet high 

 about 20-25 per cent, were infected with Diplodia 



