EFFECTS OF CHITIN AND CHITOSAN ON THE INCIDENCE AND SEVERITY OF FUSARIUM YELLOWS OF CELERY

The effects of chitin and chitosan on disease, incidence and severity of Fusarium yellows of celery and on populations of Fusarium oxysporum were investigated between 1994 and 1996. Field experiments were condu cted at two locations with a history of severe Fusarium yellows. Disea se incidence and severity were significantly reduced by pre-plant chit in amendments to soil. Chitosan applied as a root dip alone did not re duce disease incidence but significantly (P < 0.05) reduced disease se verity when used with a tolerant celery cultivar. Standard soil diluti on methods were used to enumerate populations of soil microflora, Chit in increased bacterial and actinomycete populations in soil in 2 of th e 3 years of study. The effects of potential biocontrol agents recover ed from chitin-treated plots in 1995 were studied in 1996; enriching t he transplant medium with isolates of bacteria and actinomycetes 4 wee ks and I week prior to transplanting did not alter the established equ ilibrium in the field, and no biocontrol effect was observed. Chitin a mendments to soil or chitosan treatment of transplants did not reduce soil populations of F. oxysporum. Whether these treatments affected th e F. oxysporum f. sp. apii subpopulation within the, F. oxysporum popu lation could not be determined.