Recessive Resistance Governed by a Major Quantitative Trait Locus Restricts Clover Yellow Vein Virus in Mechanically but Not Graft-Inoculated Cultivated Soybeans

Clover yellow vein virus (ClYVV) infects and causes disease in legume plants. However, here, we found that ClYVV isolate No. 30 (ClYVV-No.30) inefficiently multiplied or spread via cell-to-cell movement in mechanically inoculated leaves of a dozen soybean (Glycine max) cultivars and resulted in failure to spread systemically. Soybean plants also had a similar resistance phenotype against additional ClYVV isolates. In contrast, all but one of 24 tested accessions of wild soybeans (G. soja) were susceptible to ClYVV-No.30. Graft inoculation of cultivated soybean TK780 with ClYVV-No.30–infected wild soybean B01167 scion resulted in systemic infection of the cultivated soybean rootstock. This suggests that, upon mechanical inoculation, the cultivated soybean inhibits ClYVV-No.30, at infection steps prior to the systemic spread of the virus, via vascular systems. Systemic infection of all F1 plants from crossing between TK780 and B01167 and of 68 of 76 F2 plants with ClYVV-No.30 indicated recessive inheritance of the resistance. Further genetic analysis using 64 recombinant inbred lines between TK780 and B01167 detected one major quantitative trait locus, designated d-cv, for the resistance that was positioned in the linkage group D1b (chromosome 2). The mapped region on soybean genome suggests that d-cv is not an allele of the known resistance genes against soybean mosaic virus.