10 BULLETIN 1116, U. S. DEPARTMENT OF AGRICULTURE. 



controls. The sclerotial fungus seemed to be hardest to kill in Hon- 

 duras rice. 



The Japanese writers were treating for the control of Helminth o- 

 sporium. They recommended presoaking overnight and soaking 

 with hot water at 54° C. for 5 minutes or at 52° for 10 minutes. They 

 found that the hot-water treatment did not control Piricularia. This 

 was no doubt due to other sources of infection in the field. The hot- 

 water treatment did not prevent the black sclerotial leaf-spot in 

 Louisiana. Treated seed, untreated seed, and clean Honduras seed 

 from California produced plants which were equally diseased. The 

 fungus doubtless lives over in the soil and on old rice straw and infects 

 the rice plants the followmg season. There are strong indications 

 that this fungus produces conidia which cause the leaf infection. 

 However, this has not been proved definitely. It seems hardly 

 possible that all of the abundant infection which occurs could be 

 caused by sclerotia. 



CONCLUSIONS. 



The results given in Tables 3 and 4 show that the hot-water treat- 

 ment will kill the fungi carried within the rice seed and not injure the 

 viability of the seed if the proper methods are used. It also indicates 

 that these fungi have a tendency to lower the vitality of the seed, as 

 is shown by the better germination of seed grown in California, which 

 were relatively free internally from fungi. Hot water does not elimi- 

 nate this difference but does prevent further development of the fungi 

 in the seed, provided the seed is sown in clean soil where there is no 

 subsequent infection. 



Until more information is obtained regarding these fungi and their 

 life histories it would be inadvisable to recommend seed treatment 

 which would kill only the fungi in the seed. Where infested seed is to 

 be sown on virgin soil or soil where rice has not been grown previously, 

 it may be advisable to treat the seed to prevent introducing these 

 fungi into the new lands. Seed from California would be good for 

 this purpose without treating were it not for the numerous weed seeds 

 that might be introduced in this way. The matter of soil infestation 

 by the various fungi concerned has not been investigated sufficiently 

 to show what part it might play in seed decay and seedling blight. 



From a commercial standpoint, some form of treatment should be 

 profitable where rice is to be stored or shipped under warm, moist 

 conditions. The hot-water treatment would be too tedious and 

 expensive for treating the commercial product. It is hoped that 

 through future investigations some practicable form of treatment will 

 be discovered. A process of drying under temperatures that would 

 kill the fungi and not injure the texture of the grain might be possible. 

 Van der Wolk '^ recommended the thorough drying of rice and dry 



'Wolk, P.C. vander. Op.cit. 



