One hundred seventy bacterial strains isolated from internal tissues o
f cotton, 49 strains with known biological control activity against Rh
izoctonia solani in cotton, and 25 strains known to induce systemic re
sistance to Collectotrichum orbiculare in cucumber, were screened for
biological control potential against vascular wilt of cotton caused by
Fusarium oxysporum f. sp. vasinfectum. The strains were introduced as
endophytes in the cotton cultivar Rowden. Cotton seedlings were bacte
rized 7 days after planting by piercing stems with a fine needle that
had been brushed across actively growing colonies of each isolate. Ten
days later, the plants were inoculated by stem injection with microco
nidia of the pathogen. Twelve days after pathogen inoculation, symptom
expression was evaluated by rating disease severity with a 0 to 4 rat
ing. Six strains reduced disease severity in two separate experiments.
These strains were INR-B, JM-1128, JM-1137, CC-186, 89B-61, and JM-86
9, which were identified as Aureobacterium saperdae, Bacillus pumilus,
Phyllobacterium rubiacearum, Pseudomonas putida, P. putida, and Burkh
olderia solanacearum, respectively. Colonization studies revealed that
bacteria survived in cotton stems for up to 28 days. Five strains wer
e tested for ability to move within the stem and two demonstrated limi
ted movement, not exceeding 5.0 cm, 14 days after bacterization. Popul
ations of log 3 and log 6 CFU of strain CC-471, introduced into plant
stems, increased after 3 days to log 6.25 and to 6.63 CFU/g stem tissu
e, respectively. These results indicate that endophytic bacteria shoul
d be evaluated further for efficacy as biological control agents of va
scular pathogens and that some endophytes may survive, multiply, and e
xhibit limited movement following introduction into cotton. (C) 1995 A
cademic Press, Inc.