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Most cultivars that belong to the Rosaceae are self-incompatible and depend on cross-pollination. The pollen donor and pollen recipient have to flower synchronously and must be genetically compatible. Genetic compatibility is governed by the S-locus, which holds the S-RNase and S-haplotype-specific F-Box (SFB) genes. Thus, the S-genotype of cultivars is an important feature and is characterized molecularly by the S-RNase and SFB alleles which are distinctive for each S-haplotype. Here, we report the usage of DNA chromatography (denaturing high-performance liquid chromatography - DHPLC) for identifying the S-genotypes of European apricots on the basis of their SFB alleles. DHPLC is amenable to high-throughput automation, and therefore is valuable for breeding and for high-quality plant typing in the nursery.

Amplified fragment length polymorphism (AFLP) molecular markers were employed for the fingerprinting of 118 accessions of apricot, including cultivated varieties and related apricot species. Five primer combinations were tested and 165 polymorphic bands produced which could uniquely differentiate all accessions under investigation. Primer combinations were rated according to the multiplex ratio, the polymorphic index content and the discrimination power parameters and superior combinations were identified. AFLP markers were used in cluster analysis carried out with the UPGMA and the neighbour-joining methods and parsimony analysis. Four groups of similar accessions were identified: (i) those from the Mediterranean basin, (ii) from China, (iii) from continental Europe and (iv) mixed Europe-North America accessions. In the principal component analysis the first three components accounted for 17% of the total variability existing among accessions. Because the most important regions where apricot is cultivated in the world were represented in the analysis, with a large number of varieties, it was possible to discuss the data in the light of current phylogenetic hypotheses on the origin and evolution of the species.

The results from the evaluation of apricot seedlings for resistance to the plum pox potyvirus (sharka) are presented. The susceptibility of 291 seedlings from 19 different crosses, most of them between resistant and susceptible cultivars, was determined. The results obtained seem to indicate that the resistance to plum pox potyvirus in apricot is controlled by a single gene, where resistance would be a dominant trait and the resistant parents used would be heterozygous for this trait. Since the resistance appeared to behave as a quantitative trait during the evaluation process, the hypothesis of a monogenic control is discussed.

The level of polymorphism of the restriction fragment length polymorphisms (RFLPs) detected by 33 almond genomic and cDNA probes was studied in a set of 52 European and North-American apricot cultivars. Eighteen of these probes were polymorphic and yielded a total of 48 scorable bands, allowing the identification of 45 different phenotypes. Most cultivars (43) had an individually distinguishable RFLP phenotype, and three of the five clusters with the same phenotype contained cultivars that were likely to be synonymous. The group of Spanish cultivars (25) had a lower level of polymorphism than the others, suggesting that bottlenecks may have occurred in the recent history of the apricot that have eroded its genetic variability.

The study was carried out with 3- to 6-year-old apricot progenies from the breeding programmes of ARS in Fresno, California, USA and of CEBAS in Murcia, Spain. Progenies from 19 different crosses were studied to determine the inheritance of the genetic incompatibility trait. The 19 crosses included those where both parents were self-compatible or both self-incompatible, and also those where a self-compatible parent and another self-incompatible were crossed. Segregating progenies were studied either by bagging a sufficiently high number of flowers in balloon stage and determining the percentage of fruit set several weeks later or by following pollen tube growth with fluorescence microscopy. Results indicated that a monofactorial system with a multiallelic series appears to control the trait. Alleles for self-compatibility would allow the pollen tubes to grow in any style and reach the ovules. Alleles for self-incompatibility would stop the pollen tube growth if the same allele is present in the pollen grain and in the pistil.

Plum Pox Virus, a non-persistent virus transmitted by aphids, causes serious damage to stone fruits. The apricot tree is very sensitive and in order to breed apricot cultivars resistant to Plum Pox Virus and establish breeding strategies, genetic diversity based on 10 enzymatic systems, six of which were polymorphic, has been studied. The plant material studied, 94 accessions, included the most important apricot cultivars grown in PPV-affected areas. Genetic diversity is high and showed important differences between the three geographical groups studied (North African, European and North American). The North American group was very diverse and allozymes can be used to identify three subgroups. Some North American PPV-resistant cultivars were very distant from the rest of the cultivars, mainly due to the presence of rare alleles found in an Asian apricot related species. These results support the hypothesis that Asian-related species might be the origin of PPV resistance within the North American cultivars. Three North American cultivars have been considered as putative donors of PPV resistance to the European cultivars because of their agronomic behaviour, chilling requirements and distance from European cultivars. However, to increase the genetic variability of the European group and thereby to favour recombination, the study of Asian apricot resources is also recommended.

The investigation of acid and sugar content in an array of apricot cultivars and progenies indicates the existence of marked variability. Citric acid varied from 0.17 to 1.20% and malic acid from 0.21 to 1.51% on fresh weight. Fructose varied from 0.27 to 1.60%, glucose from 0.90 to 3.13% and sucrose from 1.92 to 6.92%. The estimate of heritability was high for total and main sugars, reaching over 0.50%. Acids generally showed low coefficients, although those for citric (0.27) and malic (0.36) were good. With the exception of one progeny, all genotype/year comparisons were not significant, showing constant patterns for acid and sugars over the years regardless of the variability in absolute values. This means that the patterns of each genotype are under genetic control. The wide range of diversity in acid and sugar content in apricot germplasm and the independent heritability for most of these compounds make it possible to breed and select cultivars with improved flavour on the basis of superior phenotypes.

Although various consensus polymerase chain reaction (PCR) primers have been reported for identifying Prunus S-alleles, they have been developed from and optimized on a limited set of alleles, which may limit their applicability to a broader allele range. To develop a primer set for use across the genus, degenerate consensus primers were designed from conserved regions of 27 S-RNase sequences available from five Prunus species. The primers were tested in 15 previously genotyped cultivars of cherry, almond and apricot, representing alleles S 1 to S 6 in each crop and also S c in apricot. Comparisons were made with previously published primers tested in the same 15 cultivars under reported reaction conditions. The new primers generated an amplification product for each of the 19 S-alleles whereas those previously available amplified no more than 14. The primers will be useful for genotyping and genetic studies in cultivars and wild populations.

Intact fruit from five plum × apricot hybrids, two Japanese plums and seven apricots were sampled for their volatile constituents by headspace analysis to study the transmission of biochemical flavor constituents from apricot and plum to hybrids between them. Volatiles were collected in Tenax traps, eluted with ether, and examined by gas chromatography-mass spectrometry. Forty-one compounds from seven chemical classes were identified in the fruit samples. Seven of the identified volatiles were unique to plumcot, and not present in either the plum or apricot parent. Aromatic profiles from plumcot accessions more closely resemble apricot profiles rather than plum.

The resistance of 12 apricot cultivars to the Dideron type Spanish isolate RB3.30 of plum pox potyvirus was evaluated in controlled conditions in an insect-proof greenhouse. The results of the evaluation demonstrated the resistance of the cultivars ‘Stella’, ‘Stark Early Orange’, ‘Goldrich’, ‘Harcot’, ‘NJA2’, ‘Pandora’ and ‘Avilara’ to the isolate, and the susceptibility of the cultivars ‘A1453’, ‘Bulida’,‘Currot’, ‘Real Fino’ and ‘Canino’

Resistance to sharka (plum pox potyvirus) was studied in 74 seedlings resulting from open pollination of the resistant apricot cultivar ‘Stella’. Each seedling was inoculated at the base by a chip-bud from a diseased GF305 peach tree. To follow tlie spread of virus into the scedlings. a Chip-bud of a healthy GF305 and another from a healthy sensitive Manicot apricot were grafted above the inoculation point in the order described. Six observations of symptoms were made in the leaves of the GF305 used For inoculation, the GF305-control, the Manicot-control and the ‘Stella’ seedlings during four growth cycles. An enzyme-linked immunosorbent assay (ELISA) was applied to the leaves of the ‘Stella’ seedlings. No ‘Stella’ seedling showed symptoms of sharka. Only three seedlings reacted positively to the ELISA. Substantial differences were observed in the speed of virus propagation through the ‘Stella’ seedlings, some of them showing a strong resistance to virus translocation. The possible use of the ‘Stella’ cultivar in apricot breeding programmes to obtain resistant cultivars is discussed.

Prunus mandshurica [(Maxim.) Koehne] from Central Asia is a species related to apricot and grown in China and Mongolia. This species has been used in apricot breeding as a source of frost resistance. In addition, P. mandshurica has been suggested as the possible origin of some North American apricot cultivars resistant to sharka (Plum pox virus. PPV). The aim of this work was to transmit the resistance to PPV from P. mandshurica to the Spanish apricot cultivar 'Currot' by traditional crossing. The resistance to a Dideron PPV isolate of the descendants of P. mandshurica × 'Currot' and their progenitors was evaluated under controlled conditions in a greenhouse. The results showed the susceptibility of both, the progenitors and the offspring to PPV, as being much higher than in other apricot seedlings. The results showed that the P. mandshurica accession studied is not a good progenitor in breeding apricot for PPV resistance, but just the opposite. The possible role of P. mandshurica as a source of resistance in apricot resistant cultivars is questioned.