Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 12, 1999
Publication Date: N/A
Interpretive Summary: A new virus-resistant white clover germplasm, PSVR1, was released in 1998 by the US Department of Agriculture's Agricultural Research Service and the Mississippi Agricultural and Forestry Experiment Station. PSVR1 was developed by researchers at Mississippi State, Misissippi, for resistance to peanut stunt virus (PSV). PSV causes the most widespread and serious virus disease of white clover in the southeastern US. In the absence of resistance, PSV spreads rapidly within white clover pastures, reducing forage yields and contributing to premature plant death and loss of clover in the pastures. Researchers developed the new source of disease resistance from the popular white clover variety Regal. Plants of the new germplasm are similar to Regal in appearance, growth, and adaptation, and should be useful to plant breeders in producing PSV-resistant cultivars. Disease-resistant white clover should increase the productivity and persistence of grazed pastures in the Southeast and reduce costly reseeding. Small quantities of seed are available to qualified researchers while supplies last.
Technical Abstract: PSVR1, a peanut stunt virus-resistant white clover (Trifolium repens L.), was released in 1998 by USDA-ARS and Mississippi Agricultural and Forestry Experiment Station. PSVR1 was developed for hypersensitive resistance to peanut stunt cucumovirus (PSV). Hypersensitivity originated in a PSV-free plant, clone 22R, collected in a 3-yr-old `Regal' white clover pasture where >80% of plants were infected by PSV. 22R was susceptible to alfalfa mosaic virus and white clover mosaic potexvirus, but resistant to clover yellow vein potyvirus, and hypersensitive to PSV. PSV-inoculated leaves formed small cholorotic lesions which became necrotic within 7 d, but no systemic infection developed. Hypersensitivity occurred only on young expanding leaves. 22R was grown in the field beside Regal and open- pollinated (OP1) seed was collected from 22R. Half of OP1 seedlings were hypersensitive, consistent with the hypothesis that hypersensitivity derives from a single dominant gene (P), heterozygous (Pp) in 22R. OP1 seedlings were cloned and identified as susceptible (S) or hypersensitive (H). Ten ramets each of OP1 H and S clones were grown in the field and open-pollinated(OP1a) seed was collected from H clones. Two-thirds of OP1a seedlings were hypersensitive. OP1a plants were cloned and hand-crossed with OP1 S clones. Ten plants of each cross were tested; 19 H (PP) clones were identified and polycrossed to produce first generation synthetic variety, Syn1. Syn1 seed was harvested separately for each seed parent line and 15 seedlings of each Syn1 line were polycrossed to produce second generation synthetic, PSVR1. PSVR1 is similar to Regal in appearance and growth and should be useful in producing PSV-resistant cultivars. Small quantities of seed are available to researchers while supplies last.