Variability and Host Specificity of Striga hermonthica (Del.) Benth. in Response to in-situ Root Exudates of Sorghum bicolor (L.) Moench

Striga hermonthica (Del.) Benth., Orobanchaceae, is an obligate root parasite on important cereal crops. The aim of this study is to investigate variability and host specificity in the early developmental stages of S. hermonthica parasitism in response to in-situ root exudates of sorghum. Field surveys were conducted during the seasons 2013/14 in Striga endemic areas in Sudan to collect seeds from the parasite. Fifteen S. hermonthica populations were collected. An in vivo experiment was conducted at the University of Gezira, Sudan to study the effects of in-situ root exudates of three sorghum cultivars on percentage of seed germination, haustorium initiation, attachment and penetration. 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 revealed the highest percentage of seed germination (46.9-57.5 %), haustorium initiation (73.8-77.9 %), attachment (38.4–40 %) and penetration (20.7–23.7 %) into sorghum root was induced by in-situ root exudates of sorghum cv. Abu-70 and by sorghum cv. Wad Ahmed. While, the lowest percentage of seed germination (53.5 %), haustorium initiation (45.2 %), attachment (5.8 %) and penetration (1.5 %) into sorghum root was induced by in-situ root exudates of Hakika. The results also revealed that percentage of seed germination, haustorium initiation, attachment and penetration of S. hermonthica populations collected from infected sorghum in response to sorghum in-situ root exudates was the highest. While, the percentage of seed germination, haustorium initiation, attachment and penetration of S. hermonthica populations collected from infected millet in response to sorghum in-situ root exudates was the lowest. This study confirms the existence of two levels of physiological specialization in S. hermonthica populations in Sudan. Moreover, two strains of S. hermonthica are one specific to sorghum and the other to millet.