Fusarium oxysporum Strains as Potential Striga Mycoherbicides: Molecular Characterization and Evidence for a new forma specialis

Abstract

Fusarium oxysporum isolates (Foxy 2 and PSM197) are potential, highly host specific mycoherbicides for the control of the parasitic weeds Striga hermonthica and S. asiatica. Their target weeds, Striga spp., are major biotic con- straints in cereal and legume production in semi-arid tropical Africa, where they adversely affect livelihood of millions of subsistence farmers. The aim of this study was to characterize and sequence the Striga mycoherbicides Foxy 2 & PSM197 in order to more clearly distinguish them from other morphologically similar pathogenic Fusarium oxysporum strains. The fungal isolates were cultivated on PDA medium and characterized based on the analysis of partial DNA sequence of the internal transcribed spacer (ITS) regions of the nuclear ribosomal RNA gene. Both isolates were identical in their ITS- sequence. The unique and identical ITS-sequence of the two isolates obtained, compared to the sequences of Fusarium oxysporum forma speciales deposited in GenBank along with the host specificity to Striga demonstrated in previous stud- ies, provides strong evidence to propose these pathogens of Striga as a new forma specialis (f. sp. strigae). The possibility to clearly distinguish between the new forma specialis and all pathogenic Fusarium oxysporum strains sequenced so far will facilitate and encourage the acceptance and introduction of Striga-mycoherbicides for practical field application by regulatory authorities and farmers.