Linkage among the R, Y and BI loci in table beet

Abstract

The primary pigments in table beet are the betalains, which are comprised of the red-violet betacyanins and the yellow betaxanthins. The presence of dominant alleles at two linked loci (R and Y) condition the qualitative production of betalain pigment in the beet plant. Red-pigmented roots are observed only in the presence of dominant alleles at both the R and Y loci, while white roots are conditioned by recessive alleles at the Y locus, and yellow roots by the genotype rrY-. A newly described gene ’blotchy’ (bl) conditions a blotchy or irregular pigment patterning in either red or yellow roots. The objective of the present investigation was to characterize the linkage relationships between the R and Y lociand the bl gene by evaluating segregating progenies developed from a series of matings of colored and white table beets. Due to epistatic interactions among the R, Y, and bl loci, algorithms for estimating linkage were developed using maximum-likelihood estimators for each cross. The two-point linkage estimate between the R and Y loci pooled over eight crosses was 7.4±1.7 cM. Segregation data indicated the bl gene is linked to the R and Y loci.The recombination fraction between R and bl was estimated from a pooled sample of four crosses at 16.7±10.8 cM. The most-likely gene order was R-Y-bl. These data demonstrate that the bl gene is a third locus conditioning betalain pigment production in table beet. The R-Y-bl genomic region is therefore important in the genetic control of betalain biosynthesis in table beet.