Employment of flanking codominant STS markers to estimate allelic substitution effects of a nematode resistance locus in carrot |
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Authors: | L.S. Boiteux J.R. Hyman I.C. Bach M.E.N. Fonseca W.C. Matthews P.A. Roberts P.W. Simon |
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Affiliation: | (1) Centro Nacional de Pesquisa de Hortaliças (CNPH) / EMBRAPA Hortaliças, CP 0218, CEP 70359-970 Brasília-DF, Brazil |
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Abstract: | In carrot, two codominant sequence-tagged site (STS) markers, flanking in tight linkage the Meloidogyne javanica resistance (Mj-1) locus, were employed to investigate the association between expression of resistance and locus dosage. Phenotypic expression of homozygous resistant (R); heterozygous; and homozygous susceptible (S) individuals in an F2 population of 396 F2 plants from ‘Brasília-1252’ (R) × ‘B6274’ (S) was estimated for three resistance criteria: total egg production per plant (TEP), egg production per gram of fibrous root (EPG) and root gall index (RGI). The homozygous resistant class had average values of 403.9 for TEP; 147.5 for EPG and 0.8 for RGI. The heterozygous class had 1,673; 477.3; and 0.16 whereas the homozygous susceptible class had 68,604; 11,877; and 2.54, respectively. The dominance ratio (d/a) indicated that genomic region(s) derived from the resistant parent encompass genetic factor(s) with almost complete dominance for RGI (d/a = 0.93–0.94) and incomplete dominance for transformed (TEP)0.25 and (EPG)0.25 (d/a = 0.63–0.65). Broad sense heritabilities were high varying from 72.9% for (EPG)0.25 to 86.0% for RGI. Narrow sense heritability values ranged from 55.9% for RGI to 64.3%for (TEP)0.25. Highly significant orthogonal contrasts were observed between homozygous resistant vs. heterozygous for (TEP)0.25 and (EPG)0.25. Marker-assisted selection could greatly facilitate the incorporation of the Mj-1 allele in both male-fertile and male-sterile counterpart lines in order to obtain F1 hybrids with the most effective levels of resistance. This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | Daucus carota markers Meloidogyne javanica resistance root-knot nematode |
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