Biological Control of Fusarium Wilt on Cotton by Use of Endophytic Bacteria

Abstract

Abstract One hundred seventy bacterial strains isolated from internal tissues of cotton, 49 strains with known biological control activity against Rhizoctonia solani in cotton, and 25 strains known to induce systemic resistance 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 bacterized 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 microconidia of the pathogen. Twelve days after pathogen inoculation, symptom expression was evaluated by rating disease severity with a 0 to 4 rating. Six strains reduced disease severity in two separate experiments. These strains were INR-B, JM-1128, JM-1137, CC-186, 89B-61, and JM-869, which were identified as Aureobacterium saperdae, Bacillus pumilus, Phyllobacterium rubiacearum, Pseudomonas putida, P. putida, and Burkholderia solanacearum, respectively. Colonization studies revealed that bacteria survived in cotton stems for up to 28 days. Five strains were tested for ability to move within the stem and two demonstrated limited movement, not exceeding 5.0 cm, 14 days after bacterization. Populations 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 tissue, respectively. These results indicate that endophytic bacteria should be evaluated further for efficacy as biological control agents of vascular pathogens and that some endophytes may survive, multiply, and exhibit limited movement following introduction into cotton.