A transposable element from the hAT-superfamily is responsible for the absence or globose-shape phenotype of leaf extrafloral nectaries in peach (Prunus persica L. Batsch)

International audienceMost peach (Prunus persica L. Batsch) cultivars have extrafloral nectaries (EFNs), or leaf-glands, on the leaf petioles, stipules, or margins (Gregory 1915, Okie 1998). From an extensive study, Gregory (1915) observed that the great majority of varieties was found to have well-defined gland shapes. Moreover gland-shapes were generally homogenous on typical shoots, although some cultivars could exhibit mixed glands. This author identified three main types of leaves, those with reniform glands, those with globose glands and glandless leaves. Fruit breeding programs have inadvertently produced peach cultivars with glandless leaves (Okie 1998), yet without determining the effects on either natural enemies or herbivorous pests (Scorza and Sherman 1996). Empirical observations, however, showed that the absence of EFNs resulted in a higher susceptibility to peach powdery mildew (PPM), a major disease of the peach caused by Podosphaera pannosa var. persicae (Weinhold 1961; Monet 1983). As a result, peach seedlings without leaf-glands were systematically discarded in the breeding programs. The Mendelian inheritance of the leaf-gland phenotype (E/e) was first described by Connors (1921) and the E locus was latter mapped on chromosome 7 of the peach (Dettori et al., 2001), but without identifying the genetic factor involved. In order to address the latter point and implement early diagnosis tools, we developed a mapping population of 833 progenies derived from the selfing of 'Malo Konare', a canning peach cultivar with globose leaf-glands, from Bulgarian origin. This population was used to map and investigate the genetic factor underlying the E locus, using additional resources including NGS peach resources and 148 cultivars from various origins. Our findings demonstrated that a MITE-like Moshan transposable element inserted in the gene controlling the character was responsible for the absence or globose-shape phenotype of the EFNs

Development and validation of an SNP-based new set of markers useful for early selection for Sharka disease in apricot ( P. armeniaca )

Sharka disease, due to the Plum pox virus, is a major threat to apricot trees. Most of the accessions world-wide and particularly those cultivated in Western Europe and the Mediterranean area are susceptible to the disease. A few resistance sources have been identified to date in cultivars developed in the US from a basis of Central Asian germplasm, all of these sharing the same genomic region associated with resistance to sharka in chromosome 1. Based on this, Simple sequence repeats (SSR) markers framing the MATH genes possibly responsible for the resistance have been developed in this region and a set of 2 SSRs (PGS1.21 and PGS1.24) and an indel (ZP002) was selected for identifying and discarding susceptible individuals at the plantlet stage of the apricot breeding process. However SSR markers could be difficult to implement by small teams due to the investment in hands-on time and equipment. As a consequence we turned to single nucleotide polymorphisms (SNP) to develop an alternative set of markers that could be cheaper and more easily implemented. Taking advantage of the numerous apricot genomic-sequences available at the UGAFL, we identified resistant/susceptible SNP/indel haplotypes and developed a set of three primer triplets (SP353, SP870, and SP871) based on the competitive allele-specific PCR (KASP™) technique by LGC genomics. This set was validated using a wide range of apricot accessions from different geographic origins and genetic backgrounds, concurrently with the original set of three SSRs. The new set gave similar results as the SSR-based set, was more convenient and, as a result, is now routinely used for early selection of apricot seedlings in our breeding programs