Growth Inhibitors of Sorghum vulgare Pers. from Striga hermonthica (Del.) Benth. PDF

Keywords

parasite, root, shoots

Abstract

Observations of the effects of Striga hermonthica (Del) Benth. on Sorghum vulgare Pers. before emergence of the parasite above the soil and the characteristic symptoms on sorghum of white blotches or chlorosis which differs from those due to mineral deficiency suggest that the parasite is allelopathic to its host. Investigation on the presence of growth inhibitors in S. hermonthica shoots or seeds was carried out, using inhibition of sorghum seed germination and seedling growth. Aqueous extract from striga seeds reduced the percent germination of sorghum seeds with greater effects than shoot extract. The growth of sorghum shoots and rootlets was also reduced. Aqueous extracts from striga seeds reduced the growth of sorghum shoots, but extracts from striga shoots reduced the growth of sorghum rootlets more than seed extracts. Extracts from the shoots of striga infected sorghum also reduced the growth of shoots and rootlets of sorghum seedlings. Aqueous extracts from shoots of non-infected sorghum plants did not affect the growth of either shoots or rootlets of the seedlings tested. This result indicates that S. hermonthica contains chemical inhibitors of S. vulgare. These inhibitors are present in the shoots and seeds of S. hermonthica. Various concentrations (5%, 10%, and 20%) of aqueous extracts from S. hermonthica shoots reduced the growth of the shoots of the five S. vulgare cultivars examined to different degrees.. Shoot growth of cultivars Debaikri, Dabar and Framida was reduced more than Dobbs and IS9830. The growth of the rootlets of the five cultivars was more affected than shoot growth, and significant reduction of root development was found for all seedlings and with all concentrations. The mean effect of treatments on the growth of shoots and rootlets as percentage of controls showed that susceptible cultivars Debaikri and Dabar were more affected than tolerant cultivars Framida and IS9830, and the intermediate cultivar, Dobbs. The response of the five sorghum cultivars to treatment with striga plant extracts resembles to some degree their response to striga infection. This proves that the effects of the parasite on its host resulted from inhibiting substances present in its seeds and/or its shoots.