EFFECT OF SORGHUM VARIETY ON STRIGA-HERMONTHICA PARASITISM AND REPRODUCTION

Sorghum yield loss due to Striga hermonthica is substantial and S. her monthica seed numbers in the soil are increased with the use of indige nous sorghum varieties. Emerged S. hermonthica plant density on improv ed and indigenous varieties was measured in several field tests of agr onomic practices (mainly herbicides and sorghum/cowpea intercropping). In researcher-managed trials in 1990, there were fewer emerged S. her monthica plants growing on the moderately resistant improved varieties S-35 and CS-54 than an the popular local varieties Djigari and Damoug ari, especially late in the season when S. hermonthica reproduction ta kes place. After two years of S-35, or of S-35 and CS-54 cultivation i n succession, S. hermonthica seed numbers in the soil were significant ly lower than in neighbouring plots where Djigari or Damougari had bee n grown. In a wide range of unreplicated farmers' trials there were us ually fewer emerged S. hermonthica plants on the resistant varieties t han on local varieties. In 36 trials, mean emerged S. hermonthica plan t density was 56% lower on S-35 than an Djigari. Future research shoul d focus on the role of host plant resistance in reducing or slowing th e increase of S. hermonthica seed numbers in the soil.