Genetic mapping of the loquat canker resistance gene pse-c in loquat (Eriobotrya japonica)

• Loquat canker disease, caused by Pseudomonas syringae pv. eriobotryae has been classified into three groups (A, B, and C).
• Resistance to Group C is controlled by a single recessive gene, pse-c.
• We mapped pse-c at the top of LG 3 by applying novel SSR markers designed on the basis of the ‘Golden Delicious’ apple genome sequence.
• The use of molecular markers linked to pse-c will greatly accelerate the selection of showing durable resistance.

Loquat canker disease, caused by Pseudomonas syringae pv. eriobotryae, is one of the most serious diseases of loquat (Eriobotrya japonica (Thunb.) Lindl.). We identified the linkage group and position of the resistance gene pse-c, which confers resistance to Group C of the pathogen, by using 141 seedlings derived from self-pollinated ‘Nagasakiwase’ (Pse-c/pse-c). Bulked segregant analysis revealed two RAPD markers, RAPD-OPY-03 and RAPD-OPA-18, with significant linkages to pse-c. The nucleotide sequences of these markers showed high similarity to the genome sequence of chromosomes 3 and 11 of ‘Golden Delicious’ apple. Of 448 SSR markers based on those genome sequences, five had significant linkages to pse-c. A linkage group including the pse-c gene, the two RAPD markers, and the five SSR markers spanned 37.9 cM with an average interval of 5.4 cM, and corresponded to the top of chromosome 3 of apple. The 170-bp allele of marker Chr3-ssr85 and the 184-bp allele of Chr3-ssr91 showed tight linkages with pse-c. The development of molecular markers linked to loquat canker resistance genes would be an effective way to establish marker-assisted selection and to pyramid several resistance genes in loquat breeding programs.