Striga Resistance/Tolerance in Sorghum: an Outcome of Interactive Intrinsic and Extrinsic Factors

Abstract

An experiment was conducted in two consecutive seasons (2016/17 and 2017/18) at two sites, irrigated and rain-fed environments with the objective of 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. The experiment, set in a randomized complete block design with four replicates, was laid in Striga hermonthica sick plots. 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. Data analyses indicated highly significant differences (P≤0.01) for all traits among crosses and the respective checks. Spatiotemporal variations in Striga emergence, biomass, productivity and sorghum grain yield were observed. Several crosses (35.7% of the total) showed some degree of resistance to the parasite across the environments others (54.8%) showed resistance only under irrigation. The level of resistance varied from very low (12%) to high (89%) as raveled by reductions in S. hermonthica emergence. Correlation analysis revealed, consistently, highly significant negative relation between sorghum grain yield, Striga counts at 75 days after sowing and Striga biomass at harvest (r = -0.711 and -0.685, respectively P≤0.001) in the irrigated environments, but not in their rain-fed equivalents. The study indicates coexistence of two complementary mechanisms of defense, resistance and tolerance, against S, hermonthica, in the generated crosses and suggests a crucial role for both intrinsic and extrinsic factors in determining resistance and/or tolerance to the parasite.