Biological control of Fusarium wilt of peas by organic soil amendments

Abstract

SUMMARYPure chitin added to soil significantly lessened the severity of pea wilt caused by Fusarium oxysporum f. pisi (Linf.) Snyder & Hansen. Pectin, glucose, cellulose and laminarin had less effect. In the glasshouse the wilt index was diminished by 12 % when chitin was added to inoculated soil the same day pea seedlings were planted in the soil, and by 25 and 45 % when it was added 3 and 8 weeks before transplanting. In the field, applying chitin to naturally infested soil when peas were sown decreased wilt index by 82 and by 75 % when applied 4 weeks earlier.Chitin did not affect the growth of healthy pea seedlings, suggesting that it affects wilt indirectly by changing the soil microflora. Both in the glasshouse and the field chitin greatly increased the numbers of actinomycetes, fungi and bacteria in the rhizosphere, whereas it decreased the population of P. oxysporum f. pisi. Similar microbial changes occurred in ‘wilt‐sick’ soil without plants, indicating that root exudates and debris intensified rather than determined these changes.Micro‐organisms isolated from the rhizosphere soil treated with chitin were more antagonistic towards F. oxysporum f. pisi race I, and the sterile rhizosphere extracts were also more inhibitory to its spore germination in vitro, than were those from the rhizosphere in soil without chitin. Chitin therefore seems to diminish wilt by stimulating micro‐organisms that antagonize and/or lyse the pathogen.