INHERITANCE OF RESISTANCE TO PRATYLENCHUS PENETRANS IN ALFALFA

Fifty-two alfalfa (Medicago sativa L.) clones, randomly selected from the cultivar Baker and the experimental line MNGRN-4, were evaluated f or resistance (based on nematode reproduction) to Pratylenchus penetra ns in growth chamber tests (25 C). Twenty-five clones, representing th e range of nematodes and eggs per plant, were selected and retested. F our moderately resistant and two susceptible alfalfa clones were ident ified. Inheritance of resistance to P. penetrans was studied in these six clones using a diallel mating design. The S-1, F-1, and reciprocal progenies differed for numbers of nematodes and eggs per g dry root a nd for shoot and root weights (P < 0.05). Resistance, measured as numb ers of nematodes in roots, was correlated between parental clones and their S-1 families (r = 0.94), parental clones and their half-sib fami lies (r = 0.81), and S-1 and half-sib families (r = 0.88). General com bining ability (GCA) effects were significant for nematode resistance traits. Both GCA and specific combining ability (SCA) effects were sig nificant for plant size traits, but SCA was more important than GCA in predicting progeny plant size. Reciprocal effects were significant fo r both nematode resistance and plant size traits, which may slow selec tion progress in long-term selection programs. However, the GCA effect s are large enough that breeding procedures that capitalize on additiv e effects should be effective in developing alfalfa cultivars with res istance to P. penetrans.