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

Abstract

To examine the genetic basis for the variable susceptibility of Striga hermonthica from differing zones of sub-Saharan Africa to Fusarium oxysporum f. sp. strigae (Fos) isolates Foxy-2 and FK3, 10 S. hermonthica populations from Eastern and Western Africa were phenotyped for their susceptibility response to Foxy-2 and FK3, and then genotyped with 22 simple sequence repeat (SSR) markers. There is low genetic differentiation between East African and West African S. hermonthica populations (i.e. the proportion of the total genetic variance contained in the subpopulation relative to the total genetic variance, F ST = 0.012, P < 0.05), but intermediate genetic differentiation (F ST = 0.143, P < 0.01) underlies the S. hermonthica groups that are differentiated by their phenotypic responses to Fos isolates. An expressed sequence tag SSR (EST-SSR) marker Y53 (P < 0.01) and a genomic SSR marker E1009 (P < 0.05) were associated with the S. hermonthica class susceptible to Foxy-2 and FK3 (group A). A divergent S. hermonthica class, consisting of groups with intermediate susceptibility to Foxy-2 (group B) and susceptibility to either FK3 (group C) or Foxy-2 (group D), showed no marker-trait association, instead demonstrated linkage disequilibrium decay. Owing to point substitutions and insertion-deletion mutations, the unique, protein-coding nucleotide sequence at the E1009 locus in group A was partly dissimilar to group B, but was totally distinct from groups C and D. These findings implied that the inconsistent effectiveness of a Fos isolate is better explained by genomic variation in S. hermonthica, rather than by S. hermonthica sampling zones.

Diacetoxyscirpenol, a Fusarium exometabolite, prevents efficiently the incidence of the parasitic weed Striga hermonthica

“…Sorghum (Sorghum bicolor L. Moench) seeds (cultivar PI563294) were sampled from Maradi, Niger. Our previous research studies confirmed the susceptibility of this sorghum cultivar to S. hermonthica [5,6]. The S. hermonthica and sorghum seeds were separately surface-sterilized using sodium hypochlorite, Tween 20 ® and double distilled water (ddH 2 O), then air-dried, according to the procedure of Anteyi and Rasche [5,6].…”

“…Furthermore, in Nicotiana sylvestris, pollen germination inhibition started from 20 ng mL − 1 (0.055 μM) DAS at 26.7%, but at 200 ng mL − 1 (0.55 μM), it was completely inhibited [65]. Because the variable susceptibility of diverse S. hermonthica populations to Fos isolates has been a major drawback in biocontrol of S. hermonthica [5,7], the ability of DAS to consistently inhibit seed germination of diverse S. hermonthica populations in our study is a very interesting discovery. After DAS, T-2 was the second bestperforming exometabolite tested in our study, followed by Neo.…”

“…However, with respect to the bipartite interaction between Fos and S. hermonthica, the role of genetic diversity as an underlying factor for this inconsistent effectiveness has been well studied. For instance, the classification of genetically contrasting Fos isolates (e.g., Foxy-2 and FK3) into separate vegetative compatibility groups (VCG) and mating types [13], and population genomic structure in S. hermonthica populations with varying susceptibility response to Foxy-2 and FK3 [5]. As a result, variation in the metabolome between genetically structured S. hermonthica groups were revealed through the sequenced genomic regions of the associated loci to show the differences in the protein-coding nucleotide sequences [5].…”

“…For instance, the classification of genetically contrasting Fos isolates (e.g., Foxy-2 and FK3) into separate vegetative compatibility groups (VCG) and mating types [13], and population genomic structure in S. hermonthica populations with varying susceptibility response to Foxy-2 and FK3 [5]. As a result, variation in the metabolome between genetically structured S. hermonthica groups were revealed through the sequenced genomic regions of the associated loci to show the differences in the protein-coding nucleotide sequences [5]. Meanwhile, in Fos, metabolomic studies have been mainly limited to the detection of particular secondary metabolites that are produced by the fungi and released into culture media e.g., fusaric acid and dehydrofusaric acid [3,61], and/or into the infected S. hermonthica shoot to cause phytotoxicity, e.g., beauvericin [51].…”