8 Harold Thurston Cook 



Sorauer (1886) and Tubeuf (1895) stated that wild species of Allium 

 are attacked by mildew, but did not give the specific names of the 

 suscepts. 



Cross-inoculation experiments were conducted, in the course of these 

 investigations, on four species and varieties of Allium and one species of 

 a closely related genus. The inoculum used in these experiments was 

 obtained from Allium cepa var. bulbellifera. In all cases the plants 

 were repeatedly inoculated under conditions favoring infection. Infec- 

 tion was obtained on Allium cepa and on Allium schoenoprasum Linn. 

 So far as is known, this is the first record of the disease on Allium 

 schoenoprasum, and specimens have been deposited in the herbarium 

 of the Department of Plant Pathology at Cornell University. 



Allium porrum, Allium sativum, and Nothoscordum bivalve Brit. 

 (yellow false garlic) did not become diseased when inoculated, although 

 susceptible species inoculated at the same time and under the same 

 conditions did. Field observations failed to reveal the fungus on Allium 

 tricoccum Ait. (wild leek), which grows near the onion fields at Elba. 

 Allium vineale Linn, (field garlic) also failed to become infected, 

 although it was planted in one of the experimental plots in which the 

 disease was prevalent. 



VARIETAL SUSCEPTIBILITY 



Very few investigations in regard to varietal susceptibility of onions 

 to mildew have been reported in literature. Shipley (1887) reported 

 that both red and white varieties are attacked, but that the red varieties 

 are the more resistant. Rosa (1926) observed that in California the 

 seed-stalks of the white varieties are attacked earliest and most severely, 

 and H. A. Jones (1926:69) stated: "The foreign types like Giant 

 Gibraltar, Sweet Spanish, Prizetaker, etc., with light green tops, appear 

 to be somewhat more resistant than the storage varieties like Yellow 

 Globe, Danvers, and Southport." Murphy and M'Kay (1926) reported 

 differences in the susceptibility of the varieties under their observation. 

 They based their conclusions on the percentage of dead plants, but stated 

 that at the time when the counts were made practically all of the plants 

 were diseased. Murphy and M'Kay list the nineteen varieties under 

 their observation in the order of their resistance. 



Fifty-three varieties of the common onion were grown and examined 

 under field conditions for differences in susceptibility, in the course of 

 this study, but practically 100 per cent of the plants became infected. 

 Striking differences in the number of plants with dead and with living 

 tops appeared to be due to early- or late-maturing characteristics of the 

 varieties, rather than to the mildew. The varieties tested are listed in 

 table 1. 



