Interactions of spotted stem borer Chilo partellus with wild relatives of sorghum

The levels of resistance to spotted stem borer (Chilo partellus) in sorghum are low to moderate. We therefore evaluated wild relatives of sorghum to identify accessions with high levels of resistance to this pest and studied the mechanisms of resistance. Heterosorghum (Sorghum laxiflorum), Para-sorghum (S. australiense, S. purpureo-sericeum, S. versicolor, S. matarankense, S. timorense, S. brevicallosum and S. nitidum) and Stiposorghum (S. angustum, S. ecarinatum, S. extans, S. intrans, S. interjectum and S. stipoideum) showed very high levels of resistance to stem borer. Chaetosorghum (S. macrospermum), four wild races of S. bicolor subsp. verticilliflorum and S. halepense were found to be susceptible. Under no-choice conditions, egg laying was observed on all accessions, which significantly differed among the species/accessions. Accessions belonging to Stiposorghum and Para-sorghum (S. purpureo-sericeum, S. versicolor and S. timorense) were significantly less preferred for oviposition than the resistant control, IS 2205. Accessions belonging to Stiposorghum showed slight leaf-feeding, but there was no deadheart formation. Although there was some damage in Para-sorghum, very few deadhearts were formed, and a few larvae that were recovered subsequently died. In Heterosorghum, the two accessions of S. laxiflorum were highly preferred for oviposition, and up to 82% deadhearts were recorded, but the six larvae that were recovered died within a month. Accessions belonging to Eu-sorghum showed maximum deadhearts, larval recovery and adult emergence. The results suggested that some of the wild relatives of sorghum possess high levels of resistance to C. partellus and both antixenosis and antibiosis are major components of resistance to this pest. Accessions showing high levels of resistance to stem borer can be utilized to increase the levels and diversify the bases of resistance to this pest in sorghum.