INOCULATIONS WITH BACTERIA CAUSING PLANT DISEASE x«-9 



and 8.5 may be obtained by placing a little M/10 K2HPO4 in the 

 mortar before the leaves are triturated. Sometimes viruses have to 

 be protected from rapid oxidation by means of 0.5% anhydrous 

 Na^.SOs. Just enough friction by a finger, cheesecloth, or similar 

 agent is employed to injure the leaf hairs. With viruses difficult to 

 transmit, better infection may be induced if a fine abrasive material 

 (e. g., carborundom powder, 600 mesh) is lightly dusted on the leaf 

 before it is rubbed. Some plant viruses are highly infectious. (Usu- 

 ally washing with soap and water is sufficient to remove infectious 

 material from the technician's hands.) When the mechanical 

 methods and insect vectors fail, two possibilities are left. 



Budding or another form of grafting may be employed and is 

 sometimes the only successful means of virus transmission. When 

 grafts are made, special precautions must be taken to prevent desic- 

 cation of the grafted parts before union has been accomplished. 

 This may be achieved by providing high air humidity, by suitable 

 wrappers, or by spraying the scions with one of the commercial wax 

 emulsions. 



By means of dodder (Bennett, 1940) certain viruses not otherwise 

 transmitted have been carried even from woody to herbaceous plants. 



TREATMENT WITH BACTERIAL PRODUCTS 



The metabolic products found in bacterial cultures are prepared 

 and employed in a variety of ways which are not yet well worked out. 

 Perhaps the least change occurs in the bacterial cells if they are centri- 

 fuged from a liquid culture and dried while frozen ("lyophile" appar- 

 atus described by Flosdorf and Mudd, 1935). The culture filtrate 

 may be concentrated under reduced pressure at a little above room 

 temperature and then "lyophilized" if desired. 



A fermented culture or an aqueous extract may be sterilized and 

 placed in a small container. If leaves w4th petioles or growing tops 

 are removed from the host plant and are placed with the cut sur- 

 faces in such liquids, they commonly show injury within one day if 

 much toxic material is present. Care is necessary while interpreting 

 such injury because many constituents of media may be toxic, e.g., 

 ammonia in alkaline material. Likewise, some non-parasitic as 

 well as parasitic fungi produce toxic substances in culture that are 

 not necessarily the reason for pathogenicity. 



The metabolites are commonly applied either in liquid form or in a 

 paste made with inert material, like lanolin or flour. The paste has 

 the advantage of furnishing a continuous supply of material over 

 a longer period with relatively less desiccation. It is commonly 

 applied to a wound. The liquid can be introduced into the vascular 

 system of a potted plant by placing cut roots extending from the 

 base of the pot, or a cut petiole, into a container of the material. 

 Likewise, a cup can be made from a rubber stopper and sealed on 

 a plant stem with vaseline. The cup is filled with liquid, under 

 which a cut is made into the vascular system, so that the liquid is 

 taken by the plant directly into the transpiration stream. Or finally, 

 the stem can be opened to form a small cavity which is kept filled by 



