Introgression of the Low Germination Stimulant Gene (lgs) for Striga Resistance into Elite Sudanese Sorghum Cultivars

Abstract

The study was undertaken to transfer Striga resistance genes from the donor parents IS9830, 555, SAR33, Framida, N13, ICSV006, ICSV007, PQ-34 Brhan and SRN39 and its derivatives P401, P402 and P405 to the improved, elite Sudanese sorghum cultivars, Wad Ahmed, Tabat, Butana and Arfagadamek-8 as recurrent parents with the objectives of securing high grain yield, reducing Striga seed bank, estimating genotypic performance, stability and adaptability of grain yield across environments and magnitude of genetic variance controlling Striga resistance traits in the engendered sorghum crosses. The experiment was undertaken in two consecutive seasons (2016/17 and 2017/18) at three sites constituting six environments representing the irrigated sector (Gezira Research Station Wad Medani and El suki Research Station) and the rain-fed sector (Gedarif Research Station). The experiment was set in a randomized complete block design with four replicates and was laid in Striga hermonthica sick plots in which infestation was artificially augmented annually. The F1 plants were backcrossed (BC1F1) to the recurrent cultivars to obtain BC2F1 families, which were subsequently salved for two successive generations to generate BC2F3 progenies. The data recorded for sorghum were days to 50% flowering, plant height, panicle exertion, panicle length, 100-grain biomass and grain yield. The data for Striga were counts of emerged plants at 15 days interval starting 45 days after sowing, number of capsules and biomass at harvest. Data analyses, using GenStat software, indicated highly significant differences (P≤0.01) for all traits between crosses and the respective checks. In general, phenotypic coefficients of variation (PCV) were higher than genotypic coefficients of variation (GCV) for all traits in all environments. Further the data showed high broad sense heritability and genetic advance estimates for grain yield compared to the other traits. Combined analysis of variance displayed highly significant differences (P≤0.01), among environments, genotypes and their interaction for grain yield. Twenty seven crosses, showing grain yield above the grand mean for the six environments, were identified. Striga count revealed highly significant differences (P≤0.01) among the crosses and their respective checks for sustenance of Striga emergence and subsequent development. A wide variability in Striga emergence was observed between environments and within genotypes. Several crosses (35.7% of the total) exhibited some degree of resistance to the parasite across the six environments. Others (54.8%) showed resistance only under irrigation. The level of resistance varied from very low to high. Correlation analysis revealed highly significant negative relation between grain yield, Striga count (r = -0.010 to -0.711 P≤0.001), biomass (r = -0.003 to -0.685 P≤0.001) and number of capsules (r = -0.196 to -0.606 P≤0.001) in the irrigated environments, but not in their rain-fed congeners. Striga count, biomass and number of capsules were positively correlated (0.523-0.908 and 0.305 -0.819 P≤0.001). Based on AMMI analysis the crosses Framida x AG-8, PQ-34 x BU, ICSV006 x BU, ICSV007 x BU, SAR33 x BU, SAR33 x TA, P402 x TA, PQ-34 x WA, P405 x WA, P401 x WA, Framida x WA, SAR33 x WA and Brhan x WA were identified as the most stable, endowed with good agronomic characters, Striga resistance and/or tolerance and high grain yield. It is recommended that crosses be screened for homozygosity and the resulting pure lines further examined for grain and nutrimental qualities, resistance mechanisms, potential for deployment as components of integrated S. hermonthica management strategies and/or as sources for resistance and/or tolerance for future breeding.