Myzus persicae is one of the most threatening insect pests that adversely affects pepper (Capsicum) cultivation. Resistance to aphids was previously identified in Capsicum baccatum. This study aimed at elucidating the genetics of aphid resistance in C. baccatum. A QTL analysis was carried out for M. persicae resistance in an F2 population derived from an intraspecific cross between a highly resistant plant and a susceptible plant. Survival and reproduction were used as resistance parameters. Interval mapping detected two QTLs affecting aphid survival (Rmpas-1) and reproduction (Rmprp-1), respectively, both localized in the same area and sharing the same top marker on chromosome 2. Use of this marker as co-factor in multiple-QTL mapping analysis revealed a second, minor QTL (Rmprp-2) only affecting aphid reproduction, on chromosome 4. Fine mapping confirmed the effects of Rmpas-1 and Rmprp-1 and narrowed the major QTL Rmprp-1 down to a genomic region of 96 kb which is predicted to encode four analogues of resistance genes of the receptor-like kinase family containing a leucine-rich repeat domain (LRR-RLKs). This work provides not only initial information for breeding aphid-resistant pepper varieties, but also forms the basis for future molecular analysis of gene(s) involved in aphid resistance.
Figure 2: Linkage map, LOD profiles and 1-LOD and 2-LOD support intervals for aphid resistance QTLs on linkage group 2. Blue and green lines represent the profiles for survival of original aphids and aphid reproduction, respectively. The dotted line at LOD 3.5 represents the LOD threshold. LG2, linkage group 2, is assigned to chromosome 2 of the pepper genome. Rmpas-1 and Rmprp-1 represent major resistance QTL for aphid survival and reproduction, respectively. The y-axis of the LOD profile shows the LOD score. The number at the end of the marker name indicates its physical position on the CM334 v.1.55 genome (Kim et al. 2014).