SERIES AM) SPECIES OF GENUS STBEPTOMYCES 



145 



in black soluble pigmenl on organic media. 

 It musi be conceded a1 mice thai not all 

 organisms isolated from scabby potatoes or 

 beets are able to produce a soluble brown 

 pigmenl and certainly not all are capable of 

 causing scabbiness in potatoes. 



Millard and Burr (1926) isolated a num- 

 ber of cultures from scabby potatoes and 

 beets. They proposed a key for the identifica- 

 tion of the presumably potato-disease-pro- 

 ducing actinomycetes (see Volume I, Chap- 

 ter IS). '1'he medium -elected tin- this 

 purpose (glycerol nitrate solution) could 

 hardly be considered the most desirable sub- 

 strate for bringing out the proper characters 

 for a system of classification. Some of these 

 cultures, notably S. clavifer and S. fimbri- 

 atus, definitely belong to the Scabies series. 



Baldacci and Spalla I 1950) suggested that 

 the strain of S. scabies isolated by Millard 

 and Bun- be designated as S. scabies var. 

 anglica. It is distinguished from the North 

 American species first described by Thaxter 

 as having a "gray substrate growth, a gray 

 aerial mycelium and a yellow soluble pig- 

 ment." 



The possibility that different strains or 

 races of S. scabies were responsible for the 

 infection of potatoes and mangels has been 

 fully recognized. No definite correlation has 

 been found, however, between pathogenicity 

 and cultural and other properties of the or- 

 ganism, although variants may differ from 

 the parent culture in pathogenicity. High 

 nitrogen contenl of the medium appeared to 

 inhibit production of aerial mycelium in the 

 parasitic strains but not in the saprophytes, 

 of the 20 isolates tested by Schaal I MM 1 1 on 



three different media, six did not produce 

 any spirals but 14 did. These spirals were of 

 both sinistrorse and dextrorse types. 



Taylor and Decker I L947), in a study of 

 14i] isolates obtained from -cabby potatoes, 

 beets, and radishes, used the following 

 criteria for their classification: acid-fastness; 

 starch hydrolysis: formation of dark brown 



surface ring on milk; acidification of milk; 

 reduction of nitrate to nitrite; utilization of 

 certain sugars, organic acid-, and paraffin; 

 gelatin liquefaction; pigment formation 

 from tyrosine; and maximum growth tem- 

 perature. The only true correlation between 

 specific cultural properties and the ability to 

 produce typical lesion- of potato scab was 

 obtained in the production of a dark brown 

 ring of surface growth on milk. 



The following species may be tentatively 

 included in the Scabies series: S. scabies, S. 

 hawaiiensis, and S. <j<ilti<ri. 



A number of other organisms isolated from 

 potato tubers or directly from the soil were 

 found capable of causing scab of potatoes 

 and must be included in this series. This is 

 true, for example, of .1. violaceochromogenes 

 described by Krassilnikov (1040), and of .1. 

 chromofuscus and .1. prunicolor of Gause <t 

 al. (1057). Other closely related forms have 

 been described, although pathogenicity tests 

 were not made. 



A number of forms that apparently have 

 nothing to do with scab formation, but have 

 the characteristic properties of the series may 

 also be included. 



\l. Series Lavendulae 



Charactt ristic Properties 



a. Sporophores straight or spiral-forming; 

 spores oval, smooth surface. 



b. Aerial mycelium colored lavender to 

 pale blue. 



c. Melanin-positive. 



This is one of the true chromogenic series 

 of the genus Streptomyces. Organisms be- 

 longing to the Lavendulae series are widely 

 distributed in the soil and are represented 

 there by a large number of species and varie- 

 ties. Many of them are strongly antagonistic 

 and are capable of forming various important 

 antibiotics, such as streptothricin. Wood- 

 ruff and McDaniel | 1958) reported that 90 

 per cent of all the antibiotic- produced by 



