Abstract
The genus Pyrus is characterized by an S-RNase-based gametophytic self-incompatibility (GSI) system, a mechanism that promotes outbreeding and prevents self-fertilization. While the S-genotype of the most widely known pear cultivars was already described, little is known on the S-allele variability within local accessions. The study was conducted on 86 accessions encompassing most of the local Sicilian varieties selected for their traits of agronomic interest and complemented with some accessions of related wild species (P. pyrifolia Nakai, P. amygdaliformis Vill.) and some national and international cultivars used as references. The employment of consensus and specific primers enabled the detection of 24 S-alleles combined in 48 S-genotypes. Results shed light on the distribution of the S-alleles among accessions, with wild species and international cultivars characterized by a high diversity and local accessions showing a more heterogeneous distribution of the S-alleles, likely reflecting a more complex history of hybridization. The S-allele distribution was largely in agreement with the genetic structure of the studied collection. In particular, the “wild” genetic background was often characterized by the same S-alleles detected in P. pyrifolia and P. amygdaliformis. The analysis of the S-allele distribution provided novel insight into the contribution of the wild and international cultivars to the genetic background of the local Sicilian or national accessions. Furthermore, these results provide information that can be readily employed by breeders for the set-up of novel mating schemes.
Highlights
European pear (Pyrus communis L.) is an economically important fruit tree species belonging to the Rosaceae family
S-determinant carried by the haploid genome of the pollen grain and one of the two S-alleles carried by the diploid genome of the stylar tissue results in the arrest of the pollen tube growth triggered by the “self” stylar ribonuclease (S-RNase), which acts as a cytotoxin and possibly activates programmed cell death
The germplasm in analysis consisted of 86 accessions composed of 43 local varieties (LV), 16 individuals belonging to wild related species (RS), 18 nationally cultivated varieties (NCV), and nine internationally cultivated varieties (ICV) (Table 1)
Summary
European pear (Pyrus communis L.) is an economically important fruit tree species belonging to the Rosaceae family. Like the majority of the Rosaceae, the genus Pyrus exhibits the S-RNase-based gametophytic self-incompatibility (GSI) system, evolved by flowering plants to prevent self-fertilization and promote outbreeding [1]. The GSI system prevents self-fertilization through a specific pollen–pistil recognition that selectively inhibits the growth of those pollen tubes recognized by the pistil as “self”. S-determinant carried by the haploid genome of the pollen grain and one of the two S-alleles carried by the diploid genome of the stylar tissue (self-recognition) results in the arrest of the pollen tube growth triggered by the “self” S-RNase, which acts as a cytotoxin and possibly activates programmed cell death. Self-incompatibility is generally considered an undesired trait, especially for those cultivated species in which the success of the fertilization process is essential for fruit set. The S-RNase gene is composed of five consensus conserved regions (C1, C2, C3, RC4, and C5) and the highly conserved noncanonical hexapeptide (IIWPNW); between C2 and C3 is located the hypervariable region (RHV)
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