Genetics of Resistance to Peanut Stunt, Clover Yellow Vein, and Alfalfa Mosaic Viruses in White Clover

Abstract

Peanut stunt virus (PSV), clover yellow vein virus (CYW), and alfalfa mosaic virus (AMV) reduce white clover (Trifolium repens L.) yield and persistence in the southeastern U.S. Southern regional virus resistant (SRVR) germplasm is the only white clover with resistance to these viruses, but little is known about the genetics of this resistance. Our objective was to determine the relative importance of general combining ability (GCA), specific combining ability (SCA), maternal effects, and nonmaternal reciprocal effects in the inheritance of resistance to PSV, CYW, and AMV in a diallel cross of one Tillman' and seven SRVR plants with differing virus susceptibilities. Progeny were grown in the greenhouse in three separate experiments and were inoculated with PSV, CYW, or AMV. Plants were evaluated for resistance by visual symptoms and either inoculation of ‘California Blackeye’ cowpeas, Vigna unguiculata (L.) Walp. subsp. unguiculata (for PSV and AMV) or enzyme‐linked immunosorbent assay (ELISA; for CYW). Differences among crosses for PSV, CYW, and AMV resistance were due to GCA, SCA, and nonmaternal reciprocal effects. For PSV and CYW resistance, additive genetic effects were more important than any other effects. For AMV resistance, nonadditive genetic effects and nonmaternal reciprocal effects were also important. Direction in which a cross is made is not important, because there were no consistent male or female effects of parents involved in more than one significant reciprocal effect. For this group of parents, breeding procedures utilizing additive genetic effects should be the most effective in improving the PSV, CYW, and possibly AMV resistance of white clover.