Employment of flanking codominant STS markers to estimate allelic substitution effects of a nematode resistance locus in carrot

• Published in: Euphytica 2004-01, Vol.136 (1), p.37-44
• Main Authors: BOITEUX, L. S, HYMAN, J. R, BACH, I. C, FONSECA, M. E. N, MATTHEWS, W. C, ROBERTS, P. A, SIMON, P. W
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Daucus carota; Egg production; Employment; Fundamental and applied biological sciences. Psychology; Genetics; Genetics and breeding of economic plants; Hybrids; Meloidogyne javanica; Varietal selection. Specialized plant breeding, plant breeding aims
• ISSN: 0014-2336; 1573-5060
• DOI: 10.1023/B:EUPH.0000019508.78153.dd

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 F^sub 2^ population of 396 F^sub 2^ 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)^sup 0.25^ and (EPG)^sup 0.25^ (d/a = 0.63-0.65). Broad sense heritabilities were high varying from 72.9% for (EPG)^sup 0.25^ to 86.0% for RGI. Narrow sense heritability values ranged from 55.9% for RGI to 64.3%for (TEP)^sup 0.25^. Highly significant orthogonal contrasts were observed between homozygous resistant vs. heterozygous for (TEP)^sup 0.25^ and (EPG)^sup 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 F^sub 1^ hybrids with the most effective levels of resistance.[PUBLICATION ABSTRACT]