Resistance to the alfalfa weevil in the Iranian collection of Medicago sativa

The Iranian collection of Medicago sativa (alfalfa, 502 accessions) was evaluated under field conditions to identify variation in resistance to the alfalfa weevil (Hypera postica Gyllenhal) between accessions over 4 years. Twenty-one accessions were identified as resistant (score 3) to semi-resistant (score 5) based on K-means cluster analysis. These materials were grouped into 10 groups by means of Duncan's Multiple Range Test. Susceptibility to alfalfa weevil was significantly correlated with some of the agro-morphological traits such as plant height (r = 0.314, P<0.01), regrowth rate (r = 0.435, P<0.01) and fall dormancy score (r = 0.284, P<0.01). In general, the resistant germplasm originated from elevated regions at high latitudes, where a co-evolution between the plant and the pest may have taken place. Multiple regression analysis showed a positive linear relationship between susceptibility to the alfalfa weevil and traits such as growth habit, plant height, length and width of the central leaflet and regrowth rate. The resulting bi-plot based on factor analysis ranked accessions for susceptibility to the pest. The identified germplasm should prove useful in alfalfa breeding programs to develop accessions resistant to the alfalfa weevil.