378 abstracts: mycology 



MYCOLOGY. — Physoderma disease of corn. W. H. Tisdale. Journ. 

 Agr. Res. 16: 137-154. 1919. 



The Physoderma disease of corn, which was discovered by Shaw in 

 India in 19 10 and by Barrett in the State of IlHnois in 191 1, is now 

 known to be more or less prevalent throughout the United States as far 

 westward as central Texas and Nebraska, and northward to southern 

 Minnesota and New Jersey. It causes little damage except in the South 

 Atlantic and Gulf Coast States and in the lower Mississippi Valley, 

 where there is considerable rainfall accompanied by high temperatures. 

 In these localities there may be as much as 10 per cent loss of grain. 



At a distance the disease has the appearance of a true rust, but on 

 close observation the two can be easily distinguished. The small red- 

 dish-brown spots on the blades, which are seldom more than i mm. 

 in diameter, often coalesce to give the blade a rusty appearance. On 

 the midrib, sheath, and culm, the spots are often as much as 5 mm. in 

 diameter and may be almost black, due to the abundant production of 

 dark brown sporangia in the tissues. The parenchyma tissues of the 

 sheath may be entirely destroyed, leaving nothing but a shredlike mass 

 of vascular fibers in the later stages. Plants have been seen to break 

 over before maturity, due to a girdling of the lower nodes by the fungus. 



The invaded cells are filled with dark brown zoosporangia, which live 

 over winter in the old diseased plants and in the soil. These sporangia 

 are carried by wind and spattering water to the young plants the fol- 

 lowing season, where they are lodged behind the sheaths and in the 

 buds. With sufficient free water and a high temperature (23° to 30 °C.) 

 they germinate by producing numerous uniciliate zoospores which come 

 to rest in from one to two hoiu-s and germinate by threadlike hyphae 

 which penetrate the epidermis of the host, invade a number of cells, and 

 produce within them a large number of sporangia which make the disease 

 evident. 



The most probable means of control are careful sanitation and crop 

 rotation. W. H. T. 



MYCOLOGY.— ^5!?^/^ scald. Chari.es Brooks, J. S. CoolEy, and 

 D. F. Fisher. Journ. Agr. Res. 16:195-217. 1919. 



Apple scald is a transportation and storage disease of apples. Green 

 apples are more susceptible to the disease than mature ones, and apples 

 from heavily irrigated trees more susceptible than those from trees 

 receiving more moderate irrigation. The rapidity of the development 

 of the disease increases with a rise in temperature up to 15° or 20° C. 



