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

Wild relatives of sorghum as sources of resistance to sorghum shoot fly, Atherigona soccata

The levels of resistance to shoot fly, Atherigona soccata in sorghum germplasm are low to moderate and therefore, we evaluated 17 wild relatives of sorghum under field and greenhouse conditions as an alternate source of genes for resistance to this pest. Thirty-two accessions belonging to Parasorghum, Stiposorghum and Heterosorghum did not suffer any shoot fly damage under multi-choice conditions in the field, while one accession each of Heterosorghum (Sorghum laxiflorum) and Chaetosorghum (S. macrospermum) suffered very low shoot fly damage. Accessions belonging to S. exstans (TRC 243601), S. stipoideum (TRC 243399) and S. matarankense (TRC 243576) showed absolute non-preference for oviposition under no-choice conditions. Accessions belonging to Heterosorghum, Parasorghum and Stiposorghum were preferred for oviposition, but suffered low deadheart formation. Manual infestation of seedlings with shoot fly eggs did not result in deadheart formation in some of the accessions belonging to S. exstans (TRC 243601), S. stipoideum (TRC 243399), S. matarankense (TRC 243576) and S. purpureosericeum (IS 18944). Larval mortality was recorded in main stems of the Parasorghums. Within section Sorghum, accessions belonging to S. bicolor ssp. verticilliflorum were highly susceptible to shoot fly, as were those of S. halepense. However, a few accessions such as IS 18226 (race arundinaceum) and IS 14212 (S. halepense) resulted in reduced survival and fecundity. Wild relatives of sorghum exhibited very high levels of antibiosis to A. soccata, while only low levels of antibiosis have been observed in the cultivated germplasm. Therefore, wild relatives with different mechanisms of resistance can be used as a source of alternate genes to increase the levels and diversify the basis of resistance to shoot fly, A. soccata