GENETIC-VARIATION FOR DISEASE AND NEMATODE RESISTANCES AND FORAGE QUALITY IN PERENNIAL DIPLOID AND TETRAPLOID LUCERNE POPULATIONS (MEDICAGO-SATIVA L)

Twenty-five lucerne populations of the Medicago sativa complex, which were either diploid or tetraploid and wild or cultivated, were analyse d for their resistance to four different fungal diseases and to stem n ematode. Forage quality, including stem digestibility and saponin cont ent, was also tested. Populations varied in susceptibility to the dise ases caused by Colletotrichum trifolii, Verticillium albo-atrum, Scler otinia trifoliorum and Pseudopezizza medicaginis, and to the nematode Ditylenchus dipsaci. Except for Sclerotinia rot, sativa and falcata su bspecies differed in susceptibility, but this grouping of populations did not account for the full range of variation among them. However, t he resistance to P. medicaginis was much lower in the sativa than in t he falcata populations. Populations also varied significantly in stem fiber content and digestibility. Stem digestibility was negatively cor related to forage yield. Wild sativa and falcata populations had lower fiber content and higher digestibility than cultivated sativa populat ions. The medicagenic acid was the sapogenin responsible for the anti- nutritional effect of the lucerne measured by the yellow mealworm larv ae Tenebrio molitor. The medicagenic acid content was lowest for the p ure sativa populations, highest for the pure falcata populations, and intermediate for the French sativa varieties that have some traits ori ginating from falcata germplasm. Some populations could be used in bre eding pro rams to improve disease and nematode resistance, and forage quality.