Effects of low and high saponin selection in alfalfa on agronomic and pest resistance traits and the interrelationship of these traits

Six alfalfa (Medicago sativa L.) cultivars, ‘DuPuits,’ ‘Ladak,’ ‘Lahontan,’ ‘Ranger,’ ‘Uinta,’ and ‘Vernal’ were selected for low and high saponin concentration and tested at various locations for seven agronomic traits and resistance to six diseases, five insects, and two nematodes. Although the selection for saponin concentration was effective, none of the agronomic traits (yield, foliage color, frost damage, lodging, digestibility, fraction I protein, and soluble protein) was consistently affected by the selection. High saponin concentration retarded the in vitro growth of southern blight (Sclerotium rolfsii Sacc.) but had very little effect on any of the other disease organisms studied: anthracnose (Colletrotrichum trifolii Bain); bacterial wilt (Corynebacterium insidiosum (Mc-Cull.) H. L. Jens.); common leafspot (Pseudopeziza medicaginis (Lib.) Sacc.); downy mildew (Peronospora trifoliorum deBary); and phytophthora root rot (Phytoph-thora megasperma Drechs.). High saponin concentration was also correlated with resistance to pea aphids (Acyr-thosiphon pisum (Harris)) but had no appreciable effect on chalcids (Bruchophagus roddi (Gussakovsky)), clover root curculio (Sitona hispidulus (F.)), spotted alfalfa aphid (Therioaphis maculata (Buckton)), alfalfa weevil (Hypera postica (Gyllenhal)), northern root-knot nematode (Meloildogyne hapla Chitwood), or stem nematode (Ditylenchus dipsaci (Kühn) Filip.). Significant correlations among the pest resistance traits suggest the possibility of linkages or pleiotropic factors.