BackgroundThe genetic regulation of flower color has been widely studied, notably as a character used by Mendel and his predecessors in the study of inheritance in pea.Methodology/Principal FindingsWe used the genome sequence of model legumes, together with their known synteny to the pea genome to identify candidate genes for the A and A2 loci in pea. We then used a combination of genetic mapping, fast neutron mutant analysis, allelic diversity, transcript quantification and transient expression complementation studies to confirm the identity of the candidates.Conclusions/SignificanceWe have identified the pea genes A and A2. A is the factor determining anthocyanin pigmentation in pea that was used by Gregor Mendel 150 years ago in his study of inheritance. The A gene encodes a bHLH transcription factor. The white flowered mutant allele most likely used by Mendel is a simple G to A transition in a splice donor site that leads to a mis-spliced mRNA with a premature stop codon, and we have identified a second rare mutant allele. The A2 gene encodes a WD40 protein that is part of an evolutionarily conserved regulatory complex.

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Resistance to Ascochyta blight has been demonstrated within pea germplasm. Pea genotypes show dif-Ascochyta blight of pea (Pisum sativum L.) is a fungal disease ferences in resistance or susceptibility to M. pinodes and caused by Mycosphaerella pinodes (Berk. & Bloxham) Verstergren, P. medicaginis var. pinodella that is independent of the Phoma medicaginis Malbr. & Roum. var. pinodella (L.K. Jones) Boerema, and Ascochyta pisi Lib. that can result in significant reduc-virulence of the pathogen isolate (Onfroy et al., 1999; tions to pea yield and quality. To characterize the genetics of resistance Wroth, 1998a; Xue et al., 1998). Complete resistance to and to identify molecular markers for use in plant breeding, quantitainfection by either pathogen has not been observed in tive trait loci (QTLs) affecting Ascochyta blight resistance were pea. Using different germplasm, Wroth (1999) found mapped in F 2:3 and F 2:4 families produced from a cross between resistant that resistance to M. pinodes infection showed quantibreeding line 3148-A88 and susceptible cultivar Rovar. A linkage map tative inheritance, while Clulow et al. (1991) suggested containing 96 loci on 11 linkage groups was constructed for 133 families that resistance to M. pinodes showed major gene inherfrom this cross. Resistance of progeny lines to natural Ascochyta itance. blight epidemics was examined in field trials at Medina, Western Molecular linkage maps and mapping of QTLs are Australia, in 1997, 1998, and 1999. Disease severity was assessed on valuable tools for characterizing the genetics of disease stems, leaves, and pods by means of separate rating scales. Because pea shows increased susceptibility to Ascochyta blight as it matures, resistance, localizing resistance loci on linkage maps, plant reproductive stage was assessed at the time of disease scoring and identifying linked polymorphic DNA sequences in the 1998 and 1999 trials. Thirteen QTLs were detected for Ascothat might be used for marker-assisted selection (MAS) chyta blight resistance on seven linkage groups. Eight of these QTLs during plant breeding. QTL mapping has characterized were detected in multiple environments or by multiple trait scores.

Hordeum bulbosum L. is a source of disease resistance genes that would be worthwhile transferring to barley (H. vulgare L.). To achieve this objective, selfed seed from a tetraploid H. vulgare x H. bulbosum hybrid was irradiated. Subsequently, a powdery mildew-resistant selection of barley phenotype (81882/83) was identified among field-grown progeny. Using molecular analyses, we have established that the H. bulbosum DNA containing the powdery mildew resistance gene had been introgressed into 81882/83 and is located on chromosome 2 (2I). Resistant plants have been backcrossed to barley to remove the adverse effects of a linked factor conditioning triploid seed formation, but there remains an association between powdery mildew resistance and non-pathogenic necrotic leaf blotching. The dominant resistance gene is allelic to a gene transferred from H. bulbosum by co-workers in Germany, but non-allelic to all other known powdery mildew resistance genes in barley. We propose Mlhb as a gene symbol for this resistance.

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