CITRUS scab: its cause and control. 



23 



citrus trees growing on the laboratory grounds at Orlando, Fla., 

 and in a near-by bearing grapefruit grove. In addition, a limited 

 number of tests were made in bearing groves at other points. 



The inoculum used in tliese expei-iments was from pure cultures 

 of the scab fungus isolated from the several highly susceptible citrus 

 species, from the resistant sweet orange, and from the avocado, as 

 well as from cultures received from Porto Rico. More complete data 

 relative to the source of cultures are given in Table 5. 



Table 5. — Sources of cultures of the citrus-scab fungus used in inoculation tests. 



Host 



Part. 



Isolated by— 



Date. 



From— 





Leaf - 



J. A. Stevenson... 

 H.E.Stevens 



(?) 



1917 



Porto Rico. 





do 



191G 



Florida Experiment 



■Rough lemon (?) 



(?) 



(?) 



station. 

 H.S. Fawcett. 



Leaf 



Fruit-disease in- 

 vestigations. 

 do 



1916 



Orlando, Fla. 



Do 



Old fallen leaf. 



Jan. 5, 1917 



Feb. 15, 1917 



do 



Do. 



Do 



do 



do 



Do. 



Do ... 



do 



.do 



Do. 



Do 



Dried fallen 



leaves. 

 Fruit 



do 



do 



Do. 



Do 



do 



May 20, 1917 



March, 1919 



December, 191S. . . 



April, 1919 



December, 191C — 



January, 1917 



July, 1916 



Do. 



Do 



do... . 



...do.. 



Winter Park, Fla. 



Sonr nrangp , . . 



Leaf 



do 



Orlando, Fla. 



Do 



Fruit 



..do .... 



Do. 



Sweet orange (Ruby 

 Blood). 



Sweet orange (Pineap- 

 ple). 



Satsuma orange 



King nrangp . 



Leaf 



do 



Tavares, Fla. 



... .do 



do 



Orlando, Fla. 



Fruit 



do 





Leaf 



.do 



February, 1917.... 



April, 1917 



March, 1919 



March, 1920 



November, 1919... 

 do.. .. 



Winter Garden, Fla. 



Tangerine 



do 



do 



Do. 



Tangelo 



do . . 



do. . . 



Orlando, Fla. 



Calamondm 



.do 



do . . . 



Do. 



Sweet bittersweet 



do 



do 



Do. 



Sour T?aTigjiiir 



.. .do 



do 



Do. 



Avocado 



do 



do 



April, 1918 



Homestead, Fla. 











In general the cultures were grown on potato-dextrose agar for 

 about three weeks before being used as inoculum. A liberal quan- 

 tity of the vegetative fungus was placed on wet absorbent cotton 

 wads (PI. XV, Fig. 2) . These plasters were so placed that the fungus 

 was in contact with the part to be infected, and they were then 

 covered with several layers of paraffin paper (PL XVI), except that 

 in special cases the plasters were left in contact with the parts to 

 be infected for at least 24 hours. Frequently in cool weather the 

 plasters were on 48 hours. At the expiration of this time the paper 

 and moist cotton plasters were removed, and the inoculated parts 

 left unprotected. During the progress of the work, control tests 

 were made by similar methods, except that the inoculum was not 

 used. 



Lesions resulting from artificial infections (PL I, Fig. 3) developed 

 in from 5 to 10 days after the inoculation was made, but in every 

 case final observations were deferred 15 days or more after the 

 plasters were removed. 



