228 '^he Philippine Journal of Science isis 



Control. — Fields should not be planted too thickly, so as to 

 allow for plenty of aeration. 



STEM ROT: SCLEROTIUM 



Symptoms. — Rice seedlings under certain conditions in the 

 seed beds may be attacked by a Sclerotium. When there is a 

 lack of water in seed beds, the disease appears to be at its worst. 

 The attack takes place near the ground on leaf sheath and stem. 

 Affected seedlings at first are yellowed and stunted, later they 

 turn brown and die. On the lower portions of attacked plants 

 usually a coarse dirty white mycelium is produced with round- 

 ish, brown, smooth sclerotial bodies. The stems of older plants 

 may be attacked, resulting in the production of sterile heads. 



Causal organism,. — The organism causing this trouble is a 

 common Sclerotium discussed before as producing stem rots 

 and damping off of various seedlings. It attacks the lower 

 portions of the plants just above the ground. The fungus is 

 more severe during damp weather and in seed beds that are 

 only partially flooded. It is also found within the stems of older 

 plants. 



Control. — Seed beds should be kept flooded. If the disease 

 is severe, all soil used for the growth of seedlings should bp 

 sterilized. Fields should not be planted too thickly. 



STRAIGHT, OR STERILE, HEAD 



Symptoms. — Certain varieties of rice are severely attacked 

 by a disease of the panicle. From a half to the entire head 

 may be affected. The kernels shrivel, and from a distance the 

 heads can be seen to stand straight. The cause of this sterile 

 condition, of from 50 to 100 per cent of the grains, has not been 

 determined. It appears to be due to a lack of vigor in the plants. 

 The lemma and palet of infected grains are discolored. 



Causal organism. — Bacteria and fungi are associated with 

 diseased grains. Oospora oryzetorum Sacc. is frequently found 

 on diseased heads. Stem borers are usually associated with dis- 

 eased plants. Rhizoctonia and Sclerotium attacking the base of 

 stems often cause straight or sterile head. Certain varieties 

 appear to be immune. 



Control. — No definite control can be given. 



Other fungi found on rice are Entyloma oryzae Syd., on weak- 

 ened leaves; and on rotting straw are found the following: 

 Ophiobolus oryzinu^s Sacc, Spegazzinia ornata Sacc, Sordaria 

 oryzeti Sacc, and Coniosporium oryzinum Sacc. 



