Anatomical response of resistant alfalfa infected with Verticillium albo-atrum

Two resistant clones of alfalfa (1079 and WL-5) were stubble inoculated with Verticillium albo-atrum and grown for two 6-wk growth cycles before being used in the histological study. During the third 6-wk growth period following inoculation, regrowth stems were sampled for histological study at weekly intervals for 6 wk. The pathogen was confined to the crown of the plants by vascular occlusions for 2 wk, after which it was present in the stems of clone WL-5. Clone 1079 confined the pathogen to the crown for an additional 2 wk. Histologically the clones responded similarly to V. albo-atrum until week 5 []