288 PHYSIOLOGY OF THE FUNGI 



times as much clavacin is required to inhibit the growth of Aspergillus 

 clavatus as Trichophyton mentagrophytes (Reilly et al., 1945). 



Fungi produce substances which are capable of inactivating certain 

 plant viruses. The Basidiomycetes are especially noteworthy in this 

 respect (Utech and Johnson, 1950). Extracts of Trichotheciiim roseum 

 reduce infectivity of southern bean mosaic, tobacco mosaic, and tobacco 

 necrosis viruses (Gupta and Price, 1950). These authors believe that 

 this reduced infectivity is due to increased resistance of the host. There 

 is no evidence which indicates that any of the known antibiotics are 

 involved in the destruction of plant viruses. However, antibiotics are 

 known which are effective against virus diseases in man. 



Preliminary studies indicate that certain antibiotics may be used to 

 control fungi which cause plant diseases. Actidione has been reported 

 by Vaughn et al. (1949) to control powdery mildew on beans and roses. 

 Actidione was toxic to young rose leaves at a concentration of 2.5 p.p.m. 

 but less toxic to bean plants. Laboratory tests indicated that actidione 

 is a fungistatic substance for a considerable number of plant pathogenic 

 fungi, including Sclerotinia fructicola, Cladosporium cucumerinum, and 

 Colletotrichum lagenarium. Further data on the effect of actidione on 

 plant pathogenic fungi are reported by Whiffin (1950). 



The protective action of an antibiotic obtained from an unidentified 

 species of Streptomyces against Venturia inaequalis on apple has been 

 reported by Leben and Keitt (1949). This antibiotic has been named 

 antimycin. 



Penicillin has been used successfully, to a limited extent, in controlling 

 necrosis of giant cactus, caused by Erwinia carnegieana (Boyle, 1949). 

 Injections of penicillin into the necrotic tissue apparently diffused through 

 the plant tissues for some distance, killing the bacteria. This is one of 

 the few cases in which an antibiotic has been used successfully in thera- 

 peutic treatment of plant disease. 



The principal use of antibiotics is to control disease in man and animals. 

 Only a relatively few antibiotics are useful for this purpose. In addition 

 to killing or inhibiting pathogenic organisms, an antibiotic, to be useful 

 in medicine, must be relatively nontoxic to the host. Some of the older 

 and more useful antibiotics used in medicine will be discussed in greater 

 detail on the following pages. 



Penicillin. This antibiotic drug is produced in industry by selected 

 isolates or mutants of Penicillium chrysogcnum and P. notatum. The 

 original isolate of Fleming produced from 2 to 4 units of penicillin per 

 milliliter of culture filtrate. P. chrysogenum Q-17Q has produced in 

 excess of 1,000 units per milliliter. The synthesis of penicillin is not 

 limited to species of the P. chrysogenum-notatum group but includes cer- 

 tain species of Aspergillus belonging to the A. flavus group. A few fungi 



