A QTL for non-darkening seed coat from 'Wit-rood boontje' was mapped in pinto bean population on chromosome Pv10, comprising 40 candidate genes. The seed coat colour darkens with age in some market classes of dry beans (Phaseolus vulgaris), including pinto bean. Beans with darkened seed coats are discounted in the market place, since they are believed to be associated with lower nutritional quality, increased cooking time, and decreased palatability. The objective of this research was to map a non-darkening gene from a cranberry-like bean 'Wit-rood boontje' using a recombinant inbred line population, derived from a cross between 'Wit-rood boontje' and a slow-darkening pinto bean (1533-15). The population was characterized for seed phenotype and genotyped with an Illumina BeadChip. A genetic linkage map was constructed with 1327 informative SNP markers plus an STS marker (OL4S) and an SSR marker (Pvsd-0028), previously associated with the J gene and Sd gene, respectively, as well as non-darkening and slow-darkening phenotypes. The linkage map spanned 1253.2 cM over 11 chromosomes. A major QTL for the non-darkening trait was flanked by SNP 715646341 and SNP 715646348 on chromosome Pv10. The region, which spanned 13.2 cM, explained 48% of the phenotypic variation for seed coat darkening. Forty candidate genes were identified in the QTL interval. This information can be used to develop a gene-based marker to facilitate breeding non-darkening pinto beans and may lead to a better understanding of the molecular mechanism for the postharvest darkening phenomenon in pinto bean.

Key message The gene Phvul.010G130600 which codes for a MYB was shown to be tightly associated with seed coat darkening in Phaseolus vulgaris and a single nucleotide deletion in the allele in Wit-rood disrupts a transcription activation region that likely prevents its functioning in this non-darkening genotype. Abstract The beige and white background colors of the seed coats of conventional pinto and cranberry beans turn brown through a process known as postharvest darkening (PHD). Seed coat PHD is attributed to proanthocyanidin accumulation and its subsequent oxidation in the seed coat. The J gene is an uncharacterized classical genetic locus known to be responsible for PHD in common bean (P. vulgaris) and individuals that are homozygous for its recessive allele have a non-darkening (ND) seed coat phenotype. A previous study identified a major colorimetrically determined QTL for seed coat color on chromosome 10 that was associated with the ND trait. The objectives of this study were to identify a gene associated with seed coat postharvest darkening in common bean and understand its function in promoting seed coat darkening. Amplicon sequencing of 21 candidate genes underlying the QTL associated with the ND trait revealed a single nucleotide deletion (c.703delG) in the candidate gene Phvul.010G130600 in non-darkening recombinant inbred lines derived from crosses between ND 'Witrood boontje' and a regular darkening pinto genotype. In silico analysis indicated that Phvul.010G130600 encodes a protein with strong amino acid sequence identity (70%) with a R2R3-MYB-type transcription factor MtPAR, which has been shown to regulate proanthocyanidin biosynthesis in Medicago truncatula seed coat tissue. The deletion in the 'Wit-rood boontje' allele of Phvul.010G130600 likely causes a translational frame shift that disrupts the function of a transcriptional activation domain contained in the C-terminus of the R2R3-MYB. A gene-based dominant marker was developed for the dominant allele of Phvul.010G130600 which can be used for marker-assisted selection of ND beans.Communicated by Albrecht E. Melchinger. Electronic supplementary materialThe online version of this article (https ://doi.org/10.1007/s0012 2-020-03571 -7) contains supplementary material, which is available to authorized users.

The beige background of the conventional pinto bean (Phaseolus vulgaris L.) seed coat turns brown over time due to oxidation of its proanthocyanidins. Pinto beans that have slow‐darkening (SD) or non‐darkening (ND) seed coats are more desired in the market because they are perceived to be fresh, high‐quality beans. However, correlations between the ND seed coat trait and agronomic performance have not been investigated. Therefore, the objectives of this study were to estimate variance components and broad‐sense heritabilities of agronomic and seed coat traits in pinto beans, and to determine if correlations exist between the ND seed coat trait and agronomic, sensory, and cooking traits in recombinant inbred lines, developed from crosses between ND pinto bean breeding lines, incorporating the ND gene from ‘Wit‐rood boontje’, with two regular‐darkening (RD) pinto bean varieties (‘Stampede’ in Population 1 and ‘La Paz’ in Population 2), grown in four different environments of southwest Ontario in 2016. Analysis of variance indicated significant differences between the RD and ND genotypes for grain yield, 100‐seed weight, hydration capacity, and the seed coat color parameters in both populations. The color parameter L*, which represents the whiteness of the seed coat, was selected as the main discriminative parameter between the RD and ND seed coat phenotypes. There was a weak positive genetic correlation between the ND trait and days to maturity in Population 1 (rg = .11). The ND trait showed weak negative genetic correlations with grain yield (rg = −.23 in Population 1 and rg = −.13 in Population 2). Moderately weak positive genetic correlations were found between the ND trait and hydration capacity in Population 1 (rg = .44) and Population 2 (rg = .40). The ND pinto beans were perceived as sweeter and had softer and smoother textures and shorter cooking times compared with the RD pinto beans.

ND Polar' (Reg. no. CV-349, PI 700767) is a new navy bean (Phaseolus vulgaris L.) cultivar developed by the Dry Edible Bean Breeding Program at North Dakota StateUniversity and released by the North Dakota Agricultural Experiment Station. ND Polar was developed using a modified pedigree method (F 1 -F 5 ), followed by pure line selection based on agronomic performance, disease resistance, and seed quality characteristics. With ∼16% of the total dry bean production in the United States, navy bean is the third most important market class after pinto and black. Accounting for 35% of the total production, North Dakota is the largest producer of dry bean in the United States. Between 2015 and 2021, ND Polar was tested across 23 environments in North Dakota, where seed yield was significantly higher than 'HMS Medalist', 'Blizzard', and 'Ensign' and similar to 'T9905'. ND Polar is resistant to Bean common mosaic virus and has intermediate resistance to common bacterial blight. ND Polar has desirable upright architecture to facilitate direct harvest. Under North Dakota environments, ND Polar shows an average plant height of 52 cm, has a 100-seed weight of 18.3 g, and matures in 102 days. Canning quality was rated as acceptable. Similar to the commercial checks, ND Polar is susceptible to local races/strains of the bean rust pathogen, anthracnose, and white mold. Other traits of agronomic and economic importance are within acceptable ranges.