Resistance to subterranean clover stunt virus

Abstract

In glass-house tests of 40 subterranean clover lines showing field resistance, 21 were found to be resistant. These included lines from Portugal, Spain, Morocco, Greece, Tunisia, and Australia. The resistance of the Australian varieties Tallarook and Hill's Small was confirmed. Three further lines from Australia, Hexham Smooth Stem, Hexham Hairy Stem, and Samaria, were also found to be resistant. Bass B, previously classed as resistant, gave variable results.

The level of resistance in the F₁'s from crosses between resistant and susceptible parents equalled that of the resistant parents, which indicated complete dominance of resistance. The F₂ values were somewhat higher than those of the mid-parents. Variations among resistant and susceptible parents, and among F₂'s of susceptible parents, indicated that resistance is not determined solely by a single gene. Modifiers, and probably different major genes, appear to be present.

The implications of these results for plant breeding are discussed.