Striga seed germination bioassays
To evaluate the resistance of sorghum accessions, we screened 11lgs1 sorghum genotypes identified from genotypic screening of SAP accessions for Striga germination induction. Shanqui Red, PI533839, PI656054 were used as LGS1 controls while SRN 39 was used as the lgs1 check.
Two Striga germination assays were used: (i) germination frequency using extracted sorghum root exudate and (ii) agar gel assays (Hess, Ejeta & Butler 1992). Root exudate germination assays were performed according to Jamil et al. (2022). Striga seeds were surface sterilized in 10% commercial bleach for 5 minutes followed by rinsing thoroughly with sterile milliQ water and air drying in a laminar flow for one hour. Striga seeds were then uniformly distributed (approximately 50-100 seeds each) on 9mm-fibre filter paper discs (Sartorius, Goettingen Germany) and put in 90mm-diameter petri-plates lined with moistened filter paper (Whatman, Maidstone, UK). Twelve (12) discs containing Striga seeds were transferred to each plate, sealed with parafilm, and wrapped in aluminum foil. For conditioning, Striga seeds were incubated at 30oC for 10 days. Afterwards, conditioned Strigaseeds were treated with root exudates collected from each sorghum (55 µL per disc). Six discs were used per treatment. The petri plates were sealed, wrapped in aluminum foil, and incubated for 24 h at 30oC to induce germination. Germinated and non-germinated seeds were analyzed using the SeedQuant software (Braguyet al. 2021) by observing under a binocular microscope. The germination frequency in percentage (GF %) was calculated for each replicate using the formula:
\(\text{GF}=\left(\frac{\text{Ngs}}{\text{Nts}}\right)x100\) Where Ngs  is the number of germinated seeds per disc and Nts  is the total number of seeds per disc.
Agar gel assays were performed according to Hess et al . (1992). Sorghum seeds were soaked in 70 % ethanol for 5 minutes and then in 1 % NaOCl solution for 20 mins. Seeds were rinsed thoroughly in sterile double distilled water and transferred in petri dishes lined with moist Whatman GFA filter paper (Meadow, UK). The plates were then wrapped in aluminum foil and incubated at 28 °C for 48 hrs. Conditioned S. hermonthica seeds (300 µl) were pipetted into petri dishes then water agar (0.8 %) was dispensed over the seeds to achieve even distribution. To the solidifying media, a pre-germinated sorghum seedling was placed at the edge of each plate with the tip of the root pointing across the plate. The gel-embedded host-parasite culture was incubated at 28 °C in the dark for 72 hours and scored for induction of Striga seed germination. Images were taken using a Leica MZ10F microscope and analyzed for germination using imageJ Version 1.5i (https://imagej.nih.gov/ij/). The maximum germination distance (MGD), which is the distance between the host root and the furthest germinated seeds, was used as a measure of resistance.