Effect of N-application on Sorghum Growth, Striga Infestation and the Osmotic Pressure of the Parasite in Relation to the Host

Abstract

Summary A pot experiment was carried out to investigate the effect of different rates of nitrogen (N) application on the growth and biomass yield of sorghum [Sorghum bicolor (L.) Moench], which is susceptible to attack by the phanerogamic root-parasite, Stiga hermonthica (Del.) Benth., and the effect of the different N rates on the parasite. This study was used also to test the ability of the parasite to adjust its osmotic pressure to that of the host under these varying N applications. The results show that severity of Striga attack on sorghum was the highest at zero-N application where the emergence of Striga was very early within 46 days after sowing, followed by the low N rate and the lowest attack at the higher and moderate rates of N. Similarly, the damage done by the Striga plants as determined by the total biomass of sorghum plants was the greatest at zero-N, which was 75%, followed by the high N rate with 54% reduction compared with the best N rate treatment at 1.Og N/kg soil. The optimum N rate at 1.Og N/kg soil lead to an increase in total biomass of sorghum by 337% over the zero-N application. In general, the application of N suppresses and delays Striga emergence in sorghum compared with zero-N. The osmotic pressure of the parasite was much greater than its host at the lower N rate, followed by the high rate of N; however, at the optimum N rate, the host and the parasite had practically the same osmotic pressure.