Germination response of <i>Striga hermonthica</i> ecotypes from Western Kenya upon exposure to maize root exudates

Striga hermonthica, commonly known as witchweed or ‘cereal killer', is a root hemiparasite of cereals, germinating only in response to host-induced molecules, strigolactones (SL). It continues to pose a serious threat to maize production in western Kenya, resulting in up to 100% crop failure. Percent germination of Striga is an important indicator of the virulence level of the parasite as it translates to high attachment to the host roots and varies based on the SL profile. However, specificity of Striga ecotypes when exposed to germination stimulants from host root exudates of differential testers of maize is unknown, hindering deployment of effective management strategies. The study sought to establish variations in virulence among Striga ecotypes based on crude root exudate-induced germination. We hypothesized no variation in germination responses among the Striga ecotypes. In vitro germination assays were used to determine differences in virulence among 5 Striga ecotypes collected from maize, sorghum, and finger millet fields in western Kenya using crude root exudates from two maize genotypes, WH403 (susceptible) and KSTP94 (resistant). Striga germination data was recorded by counting Striga seeds with a protruding radicle. All Striga ecotypes germinated in response to root exudates of KSTP94 and WH403. However, variations were observed among the ecotypes, (P < 0.05) with Alomodoi sorghum ecotype recording the highest germination in exudates of WH403 (81.9%). Bunyala sorghum ecotype recorded the lowest germination as induced by the genotypes WH403 (35%), and KSTP94 (37%). The two maize genotypes varied in their ability to induce Striga ecotype germination (P < 0.05). Results suggest that the virulence of Striga ecotypes could be genotypespecific. These novel outcomes necessitate using Striga germination response rate as a virulence factor in Striga virulence assays and the development of region-specific resistant genotypes. We recommend further analysis of the crude root exudates to ascertain the active compounds as well as genomic analysis of the Striga ecotypes.