Potato leafhopper (Homoptera: Cicadellidae) resistance in perennial glandular-haired alfalfa clones

Perennial glandular-haired alfalfa (Medicago) species and hybrids have been implicated with resistance to the potato leafhopper, Empoasca fabae (Harris). However, the development of potato leafhopper resistant alfalfa germplasm using the glandular hair trait has met with limited success. The objectives of this study were to quantitate and determine the association of glandular hairs with potato leafhopper resistance in 19 selected clones from an alfalfa population developed for improved vigor and disease and potato leafhopper resistance. The density of glandular hairs on the leaf midveins, petioles, and stems were measured. Selected clones were screened in a laboratory no-choice test for resistance to adult potato leafhopper feeding damage, survival, and oviposition. Differences in glandular hair densities among clones were highly significant for all plant parts measured. As the plants aged, glandular hair density among plants within clones increased and density variation decreased. Significant variation was observed among clones for all the potato leafhopper resistance variables measured. Percentage of adult mortality ranged from 13 to 96 and nymphal populations ranged from 0 to 33. Associations between glandular hair densities on petioles and stems with all the potato leafhopper resistance variables were significantly correlated but the correlations were not strong. Stem glandular hair density had the highest associations with the potato leafhopper resistant variables. The presence of a glandular hair exudate and physical entrapment of potato leafhopper nymphs or adults were not observed in the clones used in this study. Results of this study suggest that the glandular hairs present on the selected clones used in this study are associated with a compound that is toxic or repellent to the potato leafhopper. This study also demonstrates that the glandular hair trait is potentially useful in developing potato leafhopper resistant cultivars.