Phenotypic Diversity in Pre- and Post-Attachment Resistance to Striga hermonthica in a Core Collection of Rice Germplasms

In sub-Saharan Africa, upland rice cultivation is expanding into rainfed areas endemic to the root parasitic weed Striga hermonthica. We evaluated the Striga resistance of 69 accessions from the World Rice Core Collection (WRC) to estimate the phenotypic diversity within the Oryza sativa species. Pre-attachment resistance was screened based on the germination-inducing activities of the root exudates, while post-attachment resistance was screened through rhizotron evaluation. The 69 WRC accessions showed a wide variation in both pre- and post-attachment resistance. Root exudates of one accession induced 0.04% germination, and those of some accessions displayed >80% germination. In the evaluation of post-attachment resistance, the successful parasitism percentages ranged from 1.3% to 60.7%. The results of these resistance evaluations were subjected to cluster analysis, which recognized five groups: group I of 27 accessions, with high pre- and post-attachment resistance; group II of 12 accessions, with high post-attachment resistance but moderate pre-attachment resistance; group III of 4 accessions, with low pre-attachment resistance; group IV of 13 accessions, with low post-attachment resistance; and group V of 13 accessions, with low pre- and post-attachment resistance. The wide variation found in the WRC accessions will help to elucidate the genetic factors underpinning pre- and post-attachment resistance.