DISEASES DUE TO I'l-XOI, HACTERFA ETC, — GEXERALITIICS 154I 



The cracks are not only found in the tubers of potatoes, but also in the 

 roots of mangold-wurzels, swedes and turnips. Probably they also ori- 

 ginate from too miich nitrogen. 



DISEASES DUE TO FUNGI. BACl^ERIA 

 AND OTHER IvOWER PI^ANTS. 



1125-The Physiological Races of Erysiphe graminis on Wheat and Oats.— generalities. 



Reed, M. (i., iu University of Missouri, Ri-scarch BiilletinSo. 1:3, pp. i-i". Cohunbia, Mis- 

 souiT, 1916. 



From the results of Marchal, vSalmox, and the author's works the 

 morphological species Erysiphe graminis D. C. (" blanc des cereales") 

 should be made up of a considerable number of physiological races, of 

 which each develops on definite hosts and is for the most part connected 

 with only one genus. Thus, for example Erysiphe of barley lives on spe- 

 cies of the genus Hordeum, the Erysiphe of wheat on Triticum, that of rye, 

 of oats, and of meadow-grass, on Secale, Avena, and Poa respectiv^ely. 

 Sometimes it has been po.>sible to note the passage of the parasite from one 

 genus to another of the plant hosts. According to Marchal, the Erysiphe 

 of oats can grow on Arrhenatherum elatius and the Erysiphe of wheat on 

 Hordeum sylvaticmn and on some species of Aegilops. However these 

 cases are rare, for there, is even, in nature, a tendency' towards still greater 

 specialization as well as towards physiological adaptation. Salmon's 

 work follows the same lines, the Erysiphe of barley cannot attack all the 

 species of Hordeum. H. juhatum, H. murinum and H. secalinmn are immimc, 

 while H. btdbosum, H. deficiens, H. distichon, H. hexastichon, H. interme- 

 dium, Hr maritiniiim, H. vuJgare and H. zeocriton are on the contrary very 

 sensitive. Most of the varieties of Triticum vulgare are very susceptible 

 to Erysiphe, while the three varieties T. caesium, T. jerruginenm and T. 

 pyrothrix show a high power of resistance. In the present work the re- 

 sults of a long series of experiments are given relative to the physiological 

 races of Erysiphe graminis in the genera Avena and Triticum. There is 

 nothing in the experimental technique that is essentially new .inoculations 

 were made with a scalpel, but also large quantities of conidia were scattered 

 on the leaves and stem of plants. 



Triticum spp. -- The behaviour of t6i species and varieties of Triti- 

 cum has been sttidied. It is sufhcient in this place to consult the subjoin- 

 ed table where the relation of the varieties of 8 species or type.s of Triticum 

 to E. graminis is shown : 



In loi varieties the infection reaches its maximum, loo per cent, these 

 are varieties that are very susceptible to the attacks of Erysiphe. The 

 slight diminution that is seen among the 14 varieties of the second group 

 has no specific value. The simple fact that one trial has given a negative 

 result while in all the others the fungus develops freely cannot certainly 

 be interpreted as the beginning of immunity. The same thing can also 



