Biological control of cassava diseases using fluorescent pseudomonads

Abstract

Recent investigations on cassava and its relationships with Pseudomonas fluorescens and P. putida have shown (a) Isolates with none or very mild inhibition of pathogenic bacteria and fungi; (b) isolates that strongly inhibit pathogenic bacteria, with none or very mild inhibition of fungi; (c) isolates causing very strong inhibition of fungi, with none or very mild inhibition of bacteria; and (d) isolates inducing strong inhibition of both fungi and bacteria. There were more isolates able to inhibit pathogenic bacteria than fungi and P. fluorescens showed broader in vitro inhibition of the bacterial and fungal species tested than P. putida. There was also found the following in relation to the ability of these two species to promote root system growth of plantlets as related to pathogen inhibition in vitro: (a) Isolates that did not inhibit cassava pathogens in vitro or increased root growth of cassava plantlets; (b) strains showing a high inhibitory effect in vitro of cassava pathogens, but did not promote an increase in foliage or root system inoculated clones; (c) strains that did not inhibit cassava pathogens, but increased both the foliage and root systems of inoculated clones; and (d) strains that induced a strong inhibitory effect on cassava pathogens and a significant increase in the aerial parts and roots of inoculated plantlets. As a result of the aforementioned the following practical applications have been envisaged at various steps in systems of cassava aimed at increasing production: (a) Biological control of foliar pathogens; (b) biological control of preharvest root rots; (c) biological control of postharvest root rots: and (d) using strains as root promotors, i.e. to speed up and increase the root system of cassava plantlets in rapid multiplication systems. The effectiveness of the above depends upon the selection of appropriate strains or strain improvement by genetic manipulation.