DISEASES OF VARIOUS CROPS 



1034 - Researches on the Silver-scurf Disease {Spondylocladium airovirens) 



of the Potato (i). — Schitltz S. Eugknk, in Journal of Agricultural Research, Vol. VI, 

 Xo. ic, pp. 339-350. PI. Xl^V-XIyVIII. Washington, D. C, 1916. 



The researches made in connection with the potato disease kno\^■n as 

 "silver scurf", and caused by S/'o;;c/\'/oc/((r(i'///m rf/';'Ot'f>(?ws Harz., show that 

 in spite of the great differences in the size of the spores (which had led some 

 writers to assume the existence of two different species, with macrospores 

 and microspores), there realh^ exists only a single species. This follows 

 clearly from the fact that by cultivation in pure lines (namely, from a single 

 spore) conidia are obtained measuring from 18 to 64 ;j,. 5. atruvircns ex- 

 hibits a negative heliotropism, which does not materially affect the develop- 

 ment and appearance of the infection. 



In agar cultures the conidia and mycelium withstand the most intense 

 desiccation without being affected. The thermal optimum lies between 2i<^ 

 and 270, the maximum amounts to 30° C ; as regards the mininuun, gro\\i:h 

 ceases at 20-30 C, death only occurs at — 10'^ C. 



Neutral or slightly acid media are thus apparenth^ most adapted to 

 bring about the growth of the fungus. The presence of 5 per cent of sac- 

 charose in the agar prevents the formation of the spores. 



The parasite enters the tubers through the lenticels, and its mj'celium 

 over-runs the epidermis and the more superficial layers of the bark, which 

 it breaks up, producing lesions of various kinds. The epithelium breaks 

 away in the form of silvery scales (" silver-scurf ") The nutritive value of 

 the potatoes is not diminished, but their marketable value is very much 

 depreciated. 



The infested potatoes readih* carry the disease from one place to an- 

 other, and in the same locality they carry it over from one season to another ; 

 the mycelium, the conidia and sclerotia retain their vitality for a long time, 

 and as soon as the degree of humidity and temperature allow, they grow and 

 develop rapidly. 



As active means of preventing the spread of the disease the following 

 are advised : i) treating the infected tubers with a hot solution of I % mer- 

 curic chloride ; 2) maintaining a very low temperature in the places of storage ; 

 3) discarding even slightly infected potatoes when sowing. 



1035 - Tobacco Diseases and Pests in Eastern Java. — .See xo. 967 of this Buiidin. 



103G - Diplodia sp., a Melon Disease in the United States. — Meier f. c, in journal 



of Agricultural Research, Vol. VI, Xo. 4, pp. 149-152, PI. XVII. Washington, D. C, 1915. 



According to the facts reported in this preliminary notice, fruit deal- 

 ers in the United vStates have in the past few years had heav}' losses in con- 

 sequence of a disease attacking melons {CitruUus vulgaris) in railway- trucks 

 and sometimes destroying a large part of the goods or rendering them un- 

 saleable before they reach their destination. 



The first symptom of the disease is a slight discolouration of the rind, 

 which -Starts at the stalk and finally involves almost the entire surface of 



(i) See :iiso/^. Sept. 191 3, Xo. 1105 and />. X.;v. pji j, Xo. 1070. [Ed.) 



