Effects of host plant genotype and seedbank density on Striga reproduction

Prevention of seed input to the seedbank of Striga hermonthica-infested fields is an important objective of Striga management. In three consecutive years of field experimentation in Mali, Striga reproduction was studied for 10 sorghum genotypes at infestation levels ranging from 30 000 to 200 000 seeds m−2. Host resistance was identified as an important determinant of Striga reproduction, with the most resistant genotypes (N13, IS9830 and SRN39) reducing Striga reproduction by 70–93% compared with the most susceptible genotype (CK60-B). Seedbank density had a significant effect on Striga seed production. Higher seedbank density resulted in more Striga plants, which led to increased intra-specific competition and consequently a reduced level of reproduction per plant. For the most susceptible sorghum genotypes, density dependence also occurred in the earlier belowground stages. Striga reproduction continued beyond harvest. At the high infestation level just 8% of the total reproduction was realised after harvest, whereas at the low infestation level 39% was attained after harvest. Even though host-plant genotype plays a significant role in Striga reproduction, calculations indicated that only at very low infestation levels the use of the most resistant genotype was able to lower the Striga seedbank