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 constraints 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 ITSsequence. 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 studies, 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.

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“…In Kenya soil, Fusarium oxysporum f. sp. Strigae (Foxy -2) strain as suggested by Avedi et al (2014) was ineffective, need special storage facilities, their perspective has not been entirely utilized (Elzein et al 2008). The strains also release Zearalenone, Trichothecenes and Fumonisin mycotoxins which are believed to be hazardous to animal and human (DMello et al 1999).…”

“…Previous studies, revealed that some species of Alternaria have the ability to control several weeds that attack crops, for instance, A. cassia accessible as CASST mycoherbicide was used to control sickle weed, A. macrospora was also used to controls Anoda cristate weed in Soybeans (Lawrence et al 2008). In USA, A. macrospora inoculum was used to control jimsonweed (Walker, 2010, Elzein et al 2008). Alternaria sp.…”

Population genetic structure and marker–trait associations in East and West African Striga hermonthica with varying phenotypic response to Fusarium oxysporum f. sp. strigae isolates Foxy‐2 and FK3

“…Through molecular characterization of the internal transcribed spacer (ITS) sequence of the ribosomal RNA gene, Elzein et al . (2008) designated a forma specialis to Fusarium oxysporum , known as Fusarium oxysporum f. sp. strigae (Fos).…”

Striga hermonthica reduction using Fusarium oxysporum in Kenya

“…In North Ghana Fusarium oxysporum isolate Foxy 2 was isolated from a diseased S. hermonthica plant (Abbasher et al, 1995) and a new forma specialis named F. oxysporum f. sp. strigae, which causes Fusarium wilt of Striga species was identified (Elzein et al, 2008). In 2009, the same isolate was imported into Kenya and has been subsequently tested against S. hermonthica.…”