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Abstract
In the present study, the effect of gametophytic selection on the segregation of molecular markers linked and unlinked to wilt resistance loci was investigated. A homozygous resistant genotype WR315 (h1h1 h2h2) was crossed to two susceptible lines, Karikadle (H1H1 H2H2) and BG256 (h1h1 H2H2), to generate two different F1 populations. Three F1 plants from each cross were subjected to gametophytic selection by spraying a pathotoxin at flower bud initiation stage, while the remaining F1 plants in each cross were treated as control by spraying them with water. Both control and treated F1 plants were selfed to generate respective F2 populations. The seeds of control and selected F2 populations of both crosses were sown to raise the plants. The DNA from 60 to 70 plants in each treatment group were isolated and tested for presence of the markers linked and unlinked to wilt resistance loci. Both the linked and unlinked markers showed expected monogenic ratio of 3:1 individually in control population. In the selected F2 population the markers CS 27700 linked to H1 locus, A07C417 and H4G11 linked to H2 locus of wilt resistance exhibited significant deviations for monogenic and digenic ratios. The unlinked markers NCPGR93 and NCPGR48 showed expected monogenic ratios in the selected F2 population. The results demonstrated that the gametophytic selection for wilt resistance increase the frequency of resistance alleles and resistant plants in the progeny. Deviation from the expected segregation ratio of the marker closely linked to resistance loci suggests the presence of linkage drag in gametophytic selection for resistance. The significant deviation from monogenic ratio was also observed for the linked marker A07C417 in the selected F2 population of second cross BG256 × WR315. On the contrary, the segregation of markers in a different linkage not linked to resistance loci was not affected. Thus demonstrating the utility of gamete selection for resistance is increasing the frequency of resistant plant in the progeny independent of the parental genotype. Gametophytic selection can be applied in plant breeding programmes to develop wilt resistant genotypes in a short period.
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