Screening of annual exotic germplasm lines of Medicago spp. against cow pea aphid Aphis craccivora

Lucerne, Medicago sativa L., is among the most prized of forages and is grown worldwide as a feed for all classes of livestock. Among several production constraints, insect pests considered to be important ones as this crop is considered an insectary due to the large number of insects it attracts. Among several insect pests, aphids are important ones and damage crop throughout the world. They are gaining importance during summer months in western and southern India. Host resistance to aphids is poorly understood. Twenty six lucerne annual exotic Medicago accessions comprising nine species were screened against resistance to cowpea aphid Aphis craccivora under pot culture at southern regional research station at Dharwad. Accessions were scored on a 1–5 scale. Among the accessions screened, Medicago scutellata accessions (EC 541685, EC 541686, EC 547739 and EC 547741) and M. orbicularis (EC 541641) were found to be highly tolerant and no incidence of pea aphid was noticed. Genotypes like M. polymorpha accessions (EC 541648, EC 541650, EC 541653 & EC 541655), M. soleirolii (EC 547747 & EC 547745) and M. truncatula (EC 547750 & EC 547751) were found to be tolerant (up to 10% insect incidence). Germplasm lines M. suffruticosa (EC 541695), M. orbicularis (EC 547709) and M. polymorpha (EC 547715 & EC 547717) were found to be moderately tolerant (11–25%). However, genotypes like M. polymorpha (EC 547716) and M. rugosa (EC 547733) were found to be highly susceptible (>50% aphid incidence). The above annual Medicago spp. possess dense glandular stem and leaf hairs as a mechanism for insect resistance. Transfer of glandular hair trait from annual M. scutellata and M. orbicularis (EC 541641) into agronomically acceptable cultivars would increase the management options of lucerne.