GENETICS OF RESISTANCE TO PEANUT STUNT, CLOVER YELLOW VEIN, AND ALFALFA MOSAIC-VIRUSES IN WHITE CLOVER

Peanut stunt virus (PSV), clover yellow vein virus (CYVV), and alfalfa mosaic virus (AMV) reduce white clover (Trifolium repens L.) yield an d persistence in the southeastern U.S. Southern regional virus resista nt (SRVR) germplasm is the only white clover with resistance to these viruses, but little is known about the genetics of this resistance. Ou r objective was to determine the relative importance of general combin ing ability (GCA), specific combining ability (SCA), maternal effects, and nonmaternal reciprocal effects in the inheritance of resistance t o PSV, CYVV, and AMV in a diallel cross of one 'Tillman' and seven SRV R plants with differing virus susceptibilities. Progeny were grown in the greenhouse in three separate experiments and were inoculated with PSV, CYVV, or AMV. Plants were evaluated for resistance by visual symp toms and either inoculation of 'California Blackeye' cowpeas, Vigna un guiculata (L.) Walp. subsp. unguiculata (for PSV and AMV) or enzyme-li nked immunosorbent assay (ELISA; for CYVV). Differences among crosses for PSV, CYVV, and AMV resistance were due to GCA, SCA, and nonmaterna l reciprocal effects. For PSV and CYVV resistance, additive genetic ef fects were more important than any other effects. For AMV resistance, nonadditive genetic effects and nommaternal reciprocal effects were al so important. Direction in which a cross is made is not important, bec ause there were no consistent male or female effects of parents involv ed in more than one significant reciprocal effect. For this group of p arents, breeding procedures utilizing additive genetic effects should be the most effective in improving the PSV, CYVV, and possibly AMV res istance of white clover.