Lathyrus belinensis from Turkey carries a mildew resistance allele that can be introgressed into Lathyrus odoratus

Lathyrus belinensis is an endangered, yellow flowered, Lathyrus from Turkey. The species can be crossed, with difficulty, to the sweet pea, Lathyrus odoratus. L. belinensis is fully resistant to powdery mildew (Erysiphe), whereas L. odoratus is very sensitive. Analysis of the F₂ plants from the cross suggests that resistance is due to a single, dominant, locus. Introgression against L. odoratus for ten generations yielded plants indistinguishable from L. odoratus, except for being fully resistant to powdery mildew. Molecular analysis of the transcriptomes of L. belinensis, L. odoratus and the introgressed hybrid was performed. The transcriptome describes the complete set of genes expressed in a cell, with modern high-throughput sequencing (RNA-seq) being both cost effective and sensitive to mRNAs expressed even at low levels. Preliminary analysis showed sufficient single nucleotide polymorphisms (SNPs) between the parental plants to determine the origins of transcripts from the hybrid. Analysis of the transcriptomes demonstrated that there is a single block of genetic material derived from L. belinensis in the introgressed hybrid. This block of L. belinensis genetic material corresponds to 51 to 51.5 Mb on chromosome 4 of Medicago truncatula. This region contains a number of R-genes in Medicago. Fine structure mapping of hybrid plants is being used to more precisely define the resistance locus. Interestingly, the plants homozygous for the resistance allele have hairless seedpods, resembling L. belinensis. This recessive character is presumably very closely linked to mildew resistance and is of use in performing genetic mapping. L. belinensis has yellow flowers, a colour missing from cultivars of L. odoratus. Attempts are being made to transfer this yellow colour to L. odoratus.