In higher plants, the seed precursor (ovule primordia) is composed of three parts: funiculus, nucellus and chalaza, generating the latter one (II) or two (OI and II) protective maternal integuments (seed coat, SC). The appearance of a viable seed requires the coordinate growth and development of the preceding three compartments. Integuments are essentials for seed life as they nourish, protect and facilitate seed dispersion. Endosperm and integument growth and development are tightly coupled. Gymnosperm and angiosperm ovules are commonly unitegmic and bitegmic, respectively. Unusually, ategmy and threetegmy (OI, II and aril) also exist. The expression of the INO, ATS and ETT genes, involved in integument development, seems to have demonstrated that the fusion of OI and II leads to the appearance of unitegmy in higher plants. Likewise, INO expression also manifests the conservation of OI during evolution. The molecular control of SC development is constituted by a signalling network with still a multitude of gaps. The fertilization-independent development of the ovule is repressed by the FERTILIZATION INDEPENDENT SEED (FIS), a Polycomb-Repressive-Complex-2 (PRC2). Both endosperm and SC development are tightly linked to PRC2 function. As in many other developmental processes, auxin plays an essential role during ovule and SC development. Auxin transport from the endosperm to the integuments is regulated by AGL62 (AGAMOUS-LIKE 62), the encoding gene of which is specifically expressed in the endosperm to suppress its cellularization. In the absence of AGL62 (i.e. agl62 mutants), auxin remains trapped in the endosperm and the SC fails to develop (i.e. seed abortion). This update shows that auxin biosynthesis, transport and signalling play a predominant role and seem to be absolutely required in the pathway(s) that lead to SC formation, most likely not as a unique hormonal component.

Sweet cherries can be grafted onto a wide range of rootstocks belonging to the genus Prunus. The identification of sweet cherry rootstocks using morphological traits is almost impossible particularly during the dormant season, yet it is very important for the grower to know exactly the rootstock as this has a major influence on cultivar performance and agricultural practices. However, DNA-based molecular analysis carried out on actively growing shoot tips, leaves or dormant buds provides a good opportunity to reliably distinguish the rootstocks. Herein, we have integrated high-resolution melting (HRM) analysis, coupled with five simple sequence repeat (SSR) markers, in order to facilitate the identification of the most popular sweet cherry rootstocks in Greece. The five SSR loci used were highly informative and generated a unique melting curve profile of microsatellites for each of the six sweet cherry rootstocks tested. In particular, one marker, BPPCT002, with six HRM profiles was sufficient to discriminate all the sweet cherry rootstocks studied, highlighting its potential use for rootstock identification. Hence, this assay provided a flexible, cost-effective and closed-tube microsatellite genotyping method well suited to sweet cherry rootstock identification.

Sweet cherries can be grafted on a wide range of rootstocks belonging to Prunus avium, Prunus cerasus, Prunus mahaleb, Prunus angustifolia or hybrids of different Prunus species. Identification of Prunus rootstocks using morphological traits is almost impossible particularly during the dormant season. However, molecular analysis carried out on actively growing shoot tips, leaves or dormant buds provides good opportunity to reliably distinguish rootstocks. In this study, DNA was extracted from the leaves of a total of 184 sweet cherry rootstock candidates belonging to P. avium L., P. cerasus L., P. mahaleb L. and P. angustifolia L. previously selected from the north-western part of Turkey. The rootstock candidates were tested with ten simple sequence repeat (SSR) primers, developed for the Prunus genus. The primers successfully identified all rootstock candidates. The results showed that the number of alleles per locus ranged from 10 (UDAp-401, UCD-CH21 and CPSCT010) to 20 (UCD-CH31) with an average of 13.3 alleles per locus, indicating that the SSRs were highly informative. Unweighted Pair-Group Method with Arithmetic mean analysis demonstrated that P. avium accessions are closely related to P. cerasus. The reference rootstocks were clustered with their associated botanical species.

Prunus species are important commercial fruit (plums, apricot, peach and cherries), nut (almond) and ornamental trees cultivated broadly worldwide. This review compiles information from available literature on Prunus species in regard to gene flow and hybridization within this complex of species. The review serves as a resource for environmental risk assessment related to pollen mediated gene flow and the release of transgenic Prunus. It reveals thatPrunus species, especially plums and cherries show high potential for transgene flow. A range of characteristics including; genetic diversity, genetic bridging capacity, inter- and intra-specific genetic compatibility, self sterility (in most species), high frequency of open pollination, insect assisted pollination, perennial nature, complex phenotypic architecture (canopy height, heterogeneous crown, number of flowers produced in an individual plant), tendency to escape from cultivation, and the existence of ornamental and road sidePrunus species suggest that there is a tremendous and complicated ability for pollen mediated gene movement amongPrunus species. Ploidy differences amongPrunus species do not necessarily provide genetic segregation. The characteristics ofPrunu s species highlight the complexity of maintaining coexistence between GM and non-GMPrunus if there were commercial production of GMPrunus species. The results of this review suggest that the commercialization of one GMPrunus species can create coexistence issues for commercial non-GMPrunus production. Despite advances in molecular markers and genetic analysis in agroecology, there remains limited information on the ecological diversity, metapopulation nature, population dynamics, and direct measures of gene flow among different subgenera represented in thePrunus genus. Robust environmental impact, biosafety and coexistence assessments for GMPrunus species will require better understanding of the mechanisms of gene flow and hybridization among species within thePrunus species complex.

Introduction. Root-knot nematodes (Meloidogyne sp.) cause significant economic damage to Prunus species in China. One of the most economical and environmentally sustainable methods to reduce the impact of root-knot nematodes is the use of resistant rootstock cultivars. Our aim was to examine resistance to M. incognita and its mechanisms. Materials and methods. Four rootstocks were assessed: Tsukuba-4 (P. persica), Tsukuba-5 (P. persica), Nanking cherry (P. tomentosa) and wild peach (P. persica). The susceptible tomato (Lycopersicon esculentum Mill.) cultivar ‘Baiguoqiangfeng’ was used as a positive control. Results. Nematodes did not penetrate roots of Tsukuba-4 and Tsukuba-5, which were considered to be immune varieties. Nanking cherry was highly resistant to M. incognita, whereas wild peach was susceptible. Conclusion. The differences in resistance among the rootstocks were not attributed to differences in effects of root diffusates, but were related to the different structural organizations of the root tips. The epidermal structure of Tsukuba-4 and Tsukuba-5 completely prevented the penetration of second-stage juveniles of M. incognita (J2). In Nanking cherry, penetration of J2 juveniles was reduced, and the development of nematodes from the J2 to female stage was delayed.

Introduction. The Australian almond [Prunus dulcis (Miller) D.A. Webb] improvement program commenced five years ago with the main aims of developing scion and rootstock cultivars that are better adapted to local conditions, and that provide a superior product for Australian and overseas markets. Approaches used. The program has a number of approaches including breeding, virus detection and elimination, and biotechnology. The classical hybridisation approach aimed at generation of diversity is combined with research into the more targeted techniques of plant tissue culture, genetic fingerprinting, genome mapping and transformation. Cryopreservation research is important for genebank storage, and tissue culture for micropropagation of new rootstocks and for transformation. Material is screened for Prunus Necrotic Ringspot (PNRV) and Prune Dwarf (PDV) Viruses. In addition, work has commenced into identifying Australian isolates of Colletotrichum acutatum, the pathogen causing anthracnose disease of almonds. The work is conducted in collaboration with overseas research groups, to take advantage of the long experience of these programs, and to contribute to the international effort in Prunus improvement. Outcomes from the almondproject. The important outcomes achieved after the first five years of the project by the research team are listed.