Different methods of evaluation of Monilinia laxa on apricot flowers and branches

- Organic apricot production is currently not profitable. - The main obstacle to sustainable profitability is brown rot caused by the fungus Monilinia laxa (Aderh. & Ruhl). - In the current apricot germplasm no source of total resistance has been shown, but some varieties are expressing interesting levels of tolerance. - A good evaluation of the M. laxa symptoms is essential for a precise diagnosis of the infection and to appreciate differences between tolerant and susceptible varieties and genotypes

Linkage map saturation, construction, and comparison in four populations of Prunus

One of the objectives of the ISAFRUIT Project was to perform genetic analyses in four populations of Prunus, two of peach (P. persica) and two of apricot (P. armeniaca), in order to identify major genes and quantitative trait loci (QTLs) for characters related to fruit quality. This required the construction of saturated marker maps in each of these populations. Marker maps were available for an intra-specific peach × peach F2, a BC2 peach × P. davidiana (using peach as the recurrent parent), and an apricot × apricot F1. We have further saturated these maps mainly with SSR (simple sequence repeat) markers. A new map, constructed uniquely from SSRs was prepared for a fourth apricot × apricot F1 population. Using anchor markers, we compared these four maps with the reference Prunus map, constructed using an almond × peach F2 population. As previously observed, conservation of synteny and co-linearity were the general rule, providing additional evidence of the high level of similarity between all Prunus genomes. Comparisons of genetic distances between the maps suggested that those involving similar genomes had higher levels of recombination than those with more distant genomes, particularly the inter-specific crosses.The ISAFRUIT Project is funded by the European Commission under Thematic Priority 5 – Food Quality and Safety of the 6th Framework Programme of RTD (Contract No. FP6-FOOD-CT-2006-016279).Peer reviewe

Epigenetic engineering shows that a human centromere resists silencing mediated by H3K27me3/K9me3

Centromeres are characterized by the centromere-specific H3 variant CENP-A, which is embedded in chromatin with a pattern characteristic of active transcription that is required for centromere identity. It is unclear how centromeres remain transcriptionally active despite being flanked by repressive pericentric heterochromatin. To further understand centrochromatin’s response to repressive signals, we nucleated a Polycomb-like chromatin state within the centromere of a human artificial chromosome (HAC) by tethering the methyltransferase EZH2. This led to deposition of the H3K27me3 mark and PRC1 repressor binding. Surprisingly, this state did not abolish HAC centromere function or transcription, and this apparent resistance was not observed on a noncentromeric locus, where transcription was silenced. Directly tethering the reader/repressor PRC1 bypassed this resistance, inactivating the centromere. We observed analogous responses when tethering the heterochromatin Editor Suv39h1-methyltransferase domain (centromere resistance) or reader HP1α (centromere inactivation), respectively. Our results reveal that the HAC centromere can resist repressive pathways driven by H3K9me3/H3K27me3 and may help to explain how centromeres are able to resist inactivation by flanking heterochromatin

Apricot breeding: update and perspectives

Apricot seems to be a species still strongly susceptible to genetic improvement, under the aspects of environmental adaptability, resistance to diseases, and fruit quality, with perspectives also in improving fruit for specific processing products (juice, dry fruit, canning). The biggest challenge undoubtedly concerns disease resistance. About brown rot there is a double problem of resistance in buds (flowers) and in fruits, not regulated by the same genes. Still little is known about the sources of resistance, also due to the strong interference with the environmental conditions. Reliable markers associated to resistance are still to be found. More promising is the situation about Sharka virus. This disease, although from the epidemiological stand point is more dangerous than brown rot, seems to be more easily genetically controlled, since the sources of resistance are known and their transmission rather simple. Moreover, reliable protocols for indexing have been fined tuned. Some resistant cultivars are already available, although not always of commercial value, they could very interesting as parents. The strong influence of the climatic conditions on the flower differentiation are difficult to control genetically and require the selection is carried out under the same environment where the future cultivar will be introduced. On the other hand, since a strong tendency exists in the market to assign an extra-value to 'locally' and 'safely' grown crops, apricot is probably one of the few fruits closest to an image of an 'healthy' fruit commodity. This is due to its low environmental plasticity (that makes it practically impossible to be economically grown outside of restricted areas, even recurring to massive spraying program) and to its short fruiting cycle, that allows avoiding most of the pest and then the use of pesticides

Preliminary studies on the mechanisms involved in Plum Pox Virus apricot resistence

The sharka disease produced by plum pox virus, is one of the most important problems-of Prunus culture in Europe. In the case of apricot culture, this is aggravated because of the high susceptibility of European cultivars and the velocity of the disease spreading. Actually, genetic resistance is the only definitive solution and it is the main objective for breeders. Apricot susceptibility to plum pox virus has been investigated for many years and resistance to the virus has been observed in some American cultivars, in Greece. In order to optimize breeding programmes, an approach of the involved resistance mechanisms has been performed. Eight apricot cultivars were selected because of their different level of susceptibility to virus in field. Grafted onto healthy susceptible rootstock (Manicot apricot) they were inoculated by grafting or by aphids (Myzus persicae Sulzer). Symptoms, ELISA-DAS test and utilization of the biological indicator GF305 were used to characterize plant susceptibility. The resistance of cultivars to let aphids taking off viruses from infected tissues (acquisition) has been proved. Large differences were observed among varieties. This mainly concerns the percentage of infected plants by chip or aphids, the localization and velocity in apparition of symptoms, and the acquisition efficiency

QTL analysis of resistance to sharka disease in the apricot ( Prunus armeniaca L.) ‘Polonais’ × ‘Stark Early Orange’ F1 progeny

11 pages, 4 tables, 1 figure.-- Published online: 21 Dec. 2006.Different hypotheses on the genetic control of the resistance to the plum pox virus (PPV) have been reported in apricot, but there was a lack of agreement about the number of loci involved. In recent years, apricot genetic maps have been constructed from progenies derived from ‘Stark Early Orange’ or ‘Goldrich’, two main sources of resistance, three of these including the mapping of the PPV resistance loci. As the location of the locus was not precisely established, we mapped the PPV resistance loci using interval mapping (IM), composite interval mapping (CIM), and the Kruskal–Wallis non-parametric test in the F1 progeny derived from a cross between the susceptible cv. ‘Polonais’ and ’Stark Early Orange’. Four genomic regions were identified as being involved in PPV resistance. One of these mapped to the upper region of linkage group 1 of ‘Stark Early Orange’, and accounted for 56% of the phenotypic variation. Its location was similar to the one previously identified in ‘Goldrich’ and Prunus davidiana. In addition, a gene strongly associated to these major quantitative trait loci (QTL) was found to be related to PPV infection. Two putative QTLs were detected on linkage groups 3 of ‘Polonais’ and 5 of both ‘Polonais’ and ‘Stark Early Orange’ with both parametric and non-parametric methods at logarithm of odds (LOD) scores slightly above the detection threshold. The last QTL was only detected in the early stage of the infection. PPV resistance is, thus, controlled by a major dominant factor located on linkage group 1. The hypothesis of recessive factors with lower effect is discussed.This work was partly funded by the Commission of the European Union via the FAIR Program of Research and Technological Development (research project N° FAIR6-CT984345;1999–2003).Peer reviewe