Striga resistance in the wild relatives of sorghum

Witchweeds (Striga spp.) are noxious parasitic weeds that cause considerable crop damage in the semiarid tropics. Genetic control of striga is effective, although sources of resistance are limited in most crops. Useful resistance sources have been obtained in sorghum [Sorghum bicolor (L.) Moench], an important host crop that has coevolved with the parasite. Fifty-five wild accessions within the primary gene pool of sorghum and 20 sorghum cultivars were screened for resistance to Striga asiatica L. Kuntze in the laboratory. Wild sorghums assayed included S. almum Parodi, S. bicolor subsp. drummondii (Steud.) De Wet, race drummondii and race hewisonni, S. bicolor subsp. verticilliflorum (Steud.) Piper with races aethiopicum, arundinaceum, verticilliflorum, and virgatum; S. halepense (L.) Pers.; S. miliaceum; S. rhizomatores; S. sorghastrum; and S. usamberense. Wild sorghum accessions varied in their effects on S. asiatica at the preattachment level of association. Potential striga-resistance mechanisms of low germination stimulant production, germination inhibition, and low haustorial initiation activity were observed in this collection of sorghums. Some of these potential striga-resistance mechanisms, reported here for the first time, appear to be unique to wild sorghums. The results described in this study offer the possibility of introgressing valuable resistance genes from wild to cultivated sorghum.