Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/1997
Publication Date: N/A
Interpretive Summary: In prior research, we determined that alfalfa plants could have either of two types of resistance to the disease called Sclerotinia crown and stem rot. In laboratory tests, a type 1 resistance arrested disease development on infected plant about eight days after an infection while a type 2 resistance had slow but continuous development of disease. Current research tested (1) if plants with type 1 and type 2 resistance were crossed would their progenies have super levels of resistance, less resistance, or about the same level of resistance to this disease, (2) if plants with type 1 or type 2 resistance are crossed to others with the same type of resistance will the level of resistance always be the same for all crosses, and (3) if plants with resistance are self-pollinated, what type and level of resistance will the progenies have. Results indicated that plants with type 1 retained the greatest levels of resistance when they were self-pollinated and when they were crossed with plants with the same or different type of resistance. Plants with type 1 resistance are the best choices for developing resistance to Sclerotinia for new alfalfa varieties.
Technical Abstract: Two types of resistance responses have been identified for Sclerotinia crown and stem rot caused by Sclerotinia trifoliorum (Eriks) on alfalfa (Medicago sativa L.). Following a stem-tip inoculation, a plant with the type 1 resistance stops development of necrosis on the stem about eight days after inoculation but if it has the type 2 resistance there is continued slow development of necrosis. This research determined the levels of resistance in progenies from crosses of selections with same and different types of resistances to Sclerotinia, from crosses of resistant and susceptible selections and from self-fertilization of selections. Development of disease was measured from 4 to 14 d after inoculation. The crosses among selections with type 1 resistances produced progenies only with type 1 resistance. Crosses of selections with type 1 and type 2 resistances produced four progenies with type 1 resistance and four progenies with type 2 resistance. Selfing the four selections with type 1 resistance resulted in three progenies with type 1 resistance and the fourth had the type 2 resistance. One selection with type 2 resistance produced a progeny and it had the type 1 resistance. Selfing generally decreased the level of resistance in the resistant selections and increased the level of resistance in the susceptible selections. For plant breeding, the type 1 resistance appeared more useful.