Recurrent selection for tolerance to bean yellow mosaic virus in arrowleaf clover.
Pemberton I.J. | Smith G.R. | McLaughlin M.R.
Arrowleaf clover (Trifolium vesiculosum Savi) is an important forage crop in the southeastern USA, but production and persistence of arrowleaf can be limited by virus diseases. We conducted five cycles of recurrent phenotypic selection from 1986 through 1991 for tolerance to bean yellow mosaic virus (BYMV) isolate KY 2041 in arrowleaf clover. Six-week-old seedlings were mechanically inoculated with BYMV and evaluated at 100 d of age. From 300 to 1100 plants were screened per cycle, and the most tolerant 1 to 4% were hand-crossed and their progeny advanced to the next cycle. Seedling dry weights and virus disease ratings were used to estimate the level of virus tolerance of each plant. Rating methods were modified during evaluation of Cycle 5; growth parameters and chlorophyll levels were used as selection criteria. Results were compared with those from the susceptible cultivars, Yuchi, Meechee, and Amclo. Field evaluations compared survival of inoculated Cycle 3A germplasm (1991), and survival, yield, and flowering of Cycles 3A and 5 germplasm (1992), with those of the three susceptible cultivars and non-inoculated controls. Five cycles of recurrent phenotypic selection in arrowleaf clover resulted in a population possessing tolerance to BYMV. A lethal wilt gene was eliminated from the population, and field survival and dry matter production under disease pressure greatly improved. Tolerant plants maintained normal chlorophyll levels and near normal flowering rates when infected with BYMV, thus ensuring successful seed production.
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