Molecular and morphological evidence for resistance to sugarcane aphid (Melanaphis sacchari) in sweet sorghum [Sorghum bicolor (L.) Moench]

Aphids are one of the devastating pests affecting the productivity of sorghum in many countries. The aim of the present investigation was to identify sweet sorghum genotypes resistant to the sugarcane aphid, Melanaphis sacchari (Zehntner). A Sequence Characterized Amplified Region (SCAR) marker linked to an aphid-resistance gene (RMES1) was first used to prescreen for resistant genotypes in 561 sorghum accessions. Molecular assays indicated that 91 sorghum accessions in the collection had the RMES1 resistance marker allele. Of those, 26 agronomically superior sweet sorghum accessions, along with three commercial cultivars and one susceptible check, were further evaluated in two locations (Antalya, a lowland province, and Konya, a highland province) under field conditions. These accessions were scored for resistance to aphid damage under natural aphid infestations. The number of aphids counted on the plant leaves and stalks in the accessions during the growing seasons was used to score resistant genotypes on a scale of 1-5, where 1 was highly resistant (plants having 0-50 aphids/plant) and 5 was highly sensitive (plants having 1000+aphids/plant). Fumagine intensity on the leaves was also taken into consideration. Ten accessions from the lowland and one accession from the highland scored 1, indicating a high resistance to aphid infestation. A further 13 accessions scored 1 or 2 in both environments. Only two accessions scored 4, and no accession scored 5, indicating the utility of the RMES1 marker for prescreening purposes. One accession, BSS507, showed outstanding resistance to M. sacchari, with a score of 1 in both environments.