Table 1.

Examples of selection on R gene variation. This table summarizes the pattern of variation observed in intraspecies comparisons of R-gene orthologues in several plant species. Ka >Ks is interpreted as evidence of diversifying selection, while an increased time to coalescence and elevated Tajima’s D are signatures consistent with balancing selection. This table does not distinguish between the different processes that generate a signature resembling balancing selection, (see Fig. 1)

Species	Gene	Polymorphism type	Spp. recognized	Recognized effector	Putative selection	Evidence for selection	Reference
Arabidopsis thaliana	27 R-genes	Various	NA	NA	Balancing selection	~25% exhibit elevated Ka/Ks values, elevated Tajima’s D, low Fst	[40]
A. thaliana	RKS1	SNPs	Xanthomonas campestris	NA	Balancing selection	Elevated Tajima’s D 5′ of gene	[38••]
A. thaliana	RPM1	Deletion of locus	Pseudomonas syringae	avrRpm1	Balancing selection	Increased time to coalescence of presence absence polymorphism	[47]
A. thaliana	RPP13	SNPs	Hyaloperonospora arabidopsidis	ATR13, others NA	Balancing selection, diversifying selection	Ka > Ks, increased time to coalescence	[42,45]
A. thaliana	RPS2	SNPs	Pseudomonas syringae	avrRpt2	Balancing selection	Increased time to coalescence at the 5′ end of the LRR	[37]
A. thaliana	RPS4	SNPs	Pseudomonas syringae, Colletotrichum higginsianum, Ralstonia solanacearum	avrRPS4, others NA	Positive selection (selective sweep)	Reduced variation between alleles	[46]
A. thaliana	RPS5	Deletion of locus	Pseudomonas syringae	avrPphB	Balancing selection	Increased time to coalescence of presence/ absence polymorphism	[44]
Capsella rubella, Capsella grandiflora	Nine R-genes	Various	NA	NA	Balancing selection, diversifying selection	~20% exhibit increased time to coalescence, low Fst	[43]
Lactuca sativa (lettuce)	Several genes within RGC2 locus	SNPs, indels	NA	NA	Balancing selection	Trans-species polymorphism	[48]
Lycopersicon	Pto	NA	Pseudomonas syringae	avrPto, avrPtoB	Balancing selection	Elevated Pn/Ps levels, trans- species polymorphism	[34,36]
Solanum peruvianum	RCR3	SNPs	Cladosporium fulvum, Phytophthora infestans	avr2, EPIC1,2B	Balancing selection (possibly local adaptation)	Elevated Tajima’s D 3′ of gene, high Fst	[35••]