Transmission Ratio Distortion Due to the bl Gene in Table Beet

The bl gene conditions a blotchy phenotype (irregular sectors of red and white root color) in table beet ( Beta vulgaris ssp. vulgaris). Segregation of the bl gene was found to be consistent with a single recessive gene, however, some evidence for a departure from a single gene model was observed when blbl plants were used as females. In this report, segregation of the bl gene was examined in greater detail in 10 F 2 populations derived from crosses of red blotchy-rooted females (genotype blbl, denoted blotchy) with red-rooted males (BlBl, denoted red,), and 10 F2 populations derived from the reciprocal cross. In blbl x BlBl crosses, the proportion of red-rooted progeny was greater than 0.75 in seven of the crosses, and was significantly greater ( P = 0.005) in three crosses. A test for heterogeneity was significant, indicating that the proportion of red-rooted progeny differed significantly in these 10 crosses. In BlBl x blbl crosses, the proportion of red-rooted progeny was <0.75 in seven of the crosses and there were no significant departures from the expected 3:1 ratio in any of the individual crosses. However, a pooled estimate of the segregation ratio showed a significant ( P < 0.01) departure from the 3:1 ratio (pooled estimate = 0.71). These data demonstrate transmission ratio distortion at the bl locus when blbl plants are used as both females and males in matings with wild type plants, but the degree of distortion is greater when blbl plants are used as females. Ratio distortion in such crosses may be due to a variety of factors, including increased transmission of the bl gene through female or male gametes depending on the direction of the cross, reduced fitness of maternally derived blbl progeny, epigenetic phenomena, increased fitness of paternally derived blbl progeny, or linkage of the bl gene to viability genes. specific crosses. The proportion of distorted ratios was only 13% in populations derived from intraspecific crosses with these genera. Aberrant segregation in these crosses was attributed to linkage between marker genes and either pre or post zygotic viability genes. During development of molecular marker linkage maps, many workers have observed segregation distortion at molecular marker loci (Patterson et al. 1990). In most cases, these distorted loci occur more frequently in populations derived from interspecific crosses. Watson and Goldman (1997) described a gene bl conditioning a blotchy phenotype (irregular sectors of red and white root color) in table beet (Beta vulgaris ssp. vulgaris). Segregation of bl was found to be consistent with a single recessive gene in four BC 1 and two F2 populations; however, some evidence (P < 0.10 and P < 0.08) for departures from a single gene model were observed when blbl plants were used as females. In these cases, an excess of red-rooted progeny was present in blbl x BlBl matings. Further examination of the maternal and paternal transmission of bl was warranted. In this report, segregation of the bl gene was examined in 10 F2 populations derived from red blotchy-rooted females (genotype blbl, denoted blotchy) and red-rooted males (genotype BlBl, denoted red, crosses 1-10), and 10 F 2 populations derived from the reciprocal cross (crosses 11-20).