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| Host specificity of Sudan Witchweed (Striga hermonthica [Del.] Benth.) Seed Germination and Haustorium Initiation in Response to Millet Root Exudates and Extracts |
Awadallah B. Dafaallah, Abd Elgabar T. Babiker and Abbasher Awad Abbasher
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Abstract:
Witchweed [Striga hermonthica (Del.) Benth.] is obligate root-parasitic plants belonging to the Orobanchaceae family are deadly pests for major crops all over the world. The aim of this study is to investigate host specificity of Sudan witchweed (S. hermonthica) seed germination and haustorium initiation in response to millet [Pennisetum glaucum (L.) R. Br.] root exudates and extracts. Field surveys were conducted during the seasons 2013/2014 in Striga endemic areas in Sudan to collect seeds from the parasite. Fifteen S. hermonthica populations were collected. Tow in vitro experiments were conducted at the University of Gezira, Sudan to study the effects of root exudates and root extracts of millet cv. Ugandi, cv. Ashana and cv. Sudan II on percentage of seed germination and haustorium initiation. Treatments were arranged in a factorial completely randomized design with three replicates. Data were subjected to the analysis of variance (P £ 0.5). The results showed that there were significant differences in seed germination and haustorium initiation of witchweed in response to root exudates and root extracts among millet cultivars and among the witchweed populations. Moreover, the highest seed germination (61.7 - 76.4 %) and haustorium initiation (55 - 58%) percentages attained by S. hermonthica collected from parasitized millet. While the lowest seed germination (35.3 -37.1%) and haustorium initiation (14.3 -17%) percentages attained by S. hermonthica collected from parasitized sorghum. This study confirms the existence of two levels of physiological specialization in S. hermonthica populations in Sudan. Moreover, two strains of S. hermonthica are suggested, one specific to sorghum and the other to millet. The existence of host specificity within witchweed populations are suggested to be based almost entirely on differential response of Striga isolates to root exudates and root extracts from the host.
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