1920] EXPERIMENT STATION RECORD. 749 



DISEASES OF PLANTS. 



Plant disease studies, J. J. TuouxitKu {Ari:o)i(i Stfi. Rpt. 1918, pp. SOI, 

 :i02). — A serious disoaso of pepper, somewhat reseiiildiiii; tomato wilt, api»caro(l 

 at Ttii)ac and near Tucson. A serious disease of cottonwood and pojjjar trees, 

 caused by Ci/fospora chri/sospcriiia, has been found in Flafistaff, Williams, 

 Preseott, Douf^las, Nopales, Continental, and Tucson. It causes on the bark 

 of the larse branches sunken, dead, and blackened areas, having a pronounced 

 odor. These areas give rise later to the fruiting bodies, which can also be 

 seen in the tissues formed on the older bark. Affected trees live two or three 

 years, spreading the disease. Native cottonwoods, of which several siieeies 

 thrive at various altitudes in Arizona, are more resistant to this disease than 

 is the Carolina poplar. 



A study of certain fusarial diseases of plants, W. E. Manea'AL and H. 

 .lonANN (.][issouri Sta. Bui. 172 {l!i20), pp. ID, 20). — Isolations were made from 

 corn received from Missouri and from scabby wheat from ^Missouri, Iowa, and 

 Minnesota, and 40 different strains were kept growing in pure cultures. Other 

 organisms isolated and studied included Gibberello saubinctii and Diplodia. 

 Scabby wheat grains were studied as to means of disinfection, including for- 

 maldehyde, mercuric chlorid, copper sulphate, calcium hypochlorite, and hot 

 water. 



It was found possible to kill a large percentage of the scab organisms In 

 infected wheat seed by means of hot-water treatment. Shriveled grains from 

 scabby heads are not necessarily infected, this condition possibly being due to 

 the failure of food supply during growth. 



Tlie optimum temperature for vegetative growth of Diplodia is between 30 

 and S'^° C. (86 to 95° F.), that for the rest of the organisms studied from 2.5 

 to 28° C. G. saubinetii will kill corn seedlings grown under stei'ile conditions 

 in the laboratory at room temperature. 



Division of plant pathology, F. I). Heald {Wa.shington Sta. Bui. 155 (1920), 

 pp. 34-38). — The wheat smut work as here outlined has shown that a standard 

 formaldehyde solution kept in an open barrel and used continuously during 

 three months will not lose its effectiveness or injure the seed. Shallow plant- 

 ing gives less smut than deep planting, and trenching less than level planting. 

 Wide spacing, which lessens smut in resistant vai'ieties, has little effect on 

 susceptible varieties. More than 40,000 spores per grain are required to pro- 

 duce maximum smutting. The apparent existence of a minimum spore load, 

 which gives a small percentage, if any, smut, with other data obtained, point 

 to a multiple infection rather than infection from a single spore. The sack 

 and the open-tank method gave equally good protection, but the Haskell 

 method was not effective. None of the 116 varieties of winter wheat tested 

 was free from smut, though certain strains of Turkey continued to show mini- 

 mum infection. Of 86 spring varieties tested, 6 remained free from smut. 

 Regional strains of a variety show wide variations in degree of smut attacks. 



The Rhizoctonia disease work has been confined largely to experiments with 

 tomatoes and potatoes. The former gave 90 per cent of blight foUflwing inocu- 

 lation with pure cultures of Rhizoctonia, as compared with ."jS per cent in the 

 uninoculated plants. Inoculation with potato peels did not increase the blight. 

 The experiments on potato infected with Rhizoctonia showed that the corrosive 

 sublimate treatment of seed retards germination and lowers yield in cases or 

 sprouted seed stock, but it increases the percentage of clean tubers. Seeo 

 selected as visibly clean and planted without treatment gave higher yields of 

 table stock than was given by infected seed treated only after sprouting. 

 Clean treated seed gave a lower yield but a larger percentage of clean tubers 



