Genetic relationships between diploid and allotetraploid cherry species (Prunus avium, Prunus × gondouinii and Prunus cerasus)

Prunus avium L. (diploid, AA, 2n=2x=16), Prunus cerasus L. (allotetraploid, AAFF, 2n=4x=32) species, and their hybrid Prunus x gondouinii Rehd., constitute the most widely cultivated cherry tree species. P. cerasus is supposed to be an hybrid species produced by the union of unreduced P. avium gametes and normal P. fruticosa gametes. A continuum of morphological traits between these three species makes their assignation difficult. The aim of this paper is to study the genetic relationships between tetraploid and diploid cherry species. In all, 114 genotypes belonging to these species were analyzed using 75 AFLP markers. The coordinates of these genotypes on the first axis of a correspondence analysis allowed us to clearly distinguish each species, to identify misclassifications and to assign unknown genotypes to one species. We showed that there are specific alleles in P. cerasus, which are not present in the A genome of P. avium and which probably come from the F genome of P. cerasus. The frequencies of each marker in the A and the F genomes were estimated in order to identify A and F specific markers. We discuss the utility of these specific markers for finding the origin of the A and F genomes in the allopolyploid species.

Inheritance and linkage of isozyme loci in almond

The segregation of seven isozyme marker genes was investigated using eight controlled crosses in almond. The cultivar 'Nonpareil' was the maternal parent in all crosses. Pollination was achieved using eight different cultivars, and a total of 3200 individual kernels were assessed. For each isozyme the goodness-of-fit test was used to test for departure from the expected frequencies assuming Mendelian inheritance. Given a higher than expected number of significant results for individual isozymes, independent segregation between pairs of isozymes was tested using the chi-square statistic on the resulting two-way contingency tables. In all crosses a highly significant association (P value< 0.001) was observed between (1) the AAT- 1 and IDH isozymes loci and (2) the LAP-1 and PGM-2 isozymes loci, which leads to the conclusion that the respective isozyme pairs are linked.In addition, a significant association (P value < 0.001) was observed between LAP-1 and GPI-2 when the pollen sources were 'Fritz', 'Mission', or 'Price', but this could not be tested for the remaining five pollen sources, 'Carmel', 'Grant', 'Keane', 'Ne plus Ultra', 'Peerless', because they are homozygous at these loci. If LAP-1 is linked with GPI-2 and PGM-2, it might be expected that we should find evidence of linkage between GPI-2 and PGM-2. The lack of a significant association between these two isozymes suggests that LAP-1 is located centrally on the chromosome. These three pairs of linked loci are the first to be reported in almond.

Isozyme diversity in sour, sweet, and ground cherry

Thirty-six sour (Prunus cerasus L.), sweet (P. avium L.), and ground cherry (P. fruticosa Pall.) selections were evaluated for seven enzyme systems and principal coordinate analysis was used to examine isozyme divergence among these cherry species. The enzyme systems studied were phosphoglucose isomerase (PGI), isocitrate dehydrogenase (IDH), phosphoglucomutase (PGM), 6-phosphogluconate dehydrogenase (6-PGD), leucine aminopeptidase (LAP), shikimate dehydrogenase (SKDH), and malate dehydrogenase (MDH). The first principal coordinate, which accounted for 41% of the total variation, separated the diploid sweet cherry selections from the sour, ground, and sour x ground cherry tetraploids. An additional 86 selections were evaluated for up to six of the enzyme systems to determine the polymorphisms at the enzyme loci and the level of heterozygosity between the diploid sweet cherry and the tetraploid species and interspecific hybrids. 6-PGD was the most polymorphic enzyme exhibiting 16 patterns. The tetraploid cherry species were more heterozygous than the diploid sweet cherry with an average heterozygosity of 78% compared to 19% for the diploids.

Targeted mapping and linkage analysis of morphological isozyme, and RAPD markers in peach

Nine different F2 families of peach [Prunus persica (L.) Batsch] were analyzed for linkage relationships between 14 morphological and two isozyme loci. Linkage was detected between weeping (We) and white flower (W), 33 cM; double flower (Dl) and pillar (Br), 10 cM; and flesh color (Y) and malate dehydrogenase (Mdh1), 26 cM. A leaf variant phenotypically distinct from the previously reported wavy-leaf (Wa) mutant in peach was found in progeny of 'Davie II'. The new willow-leaf character (designated Wa2) was closely linked (0.4 cM) to a new dwarf phenotype (designated Dw3). Two families derived from the pollen-fertile cultivar 'White Glory' segregated for pollen sterility, but segregation did not follow a 3∶1 ratio. Evidence is presented suggesting that 'White Glory' possesses a pollen-sterility gene (designated Ps2) that is non-allelic to the previously reported pollen-sterility gene (Ps) in peach. Ps2 was linked to both weeping (We-Ps2, 15.5 cM) and white flower (Ps2-W, 25.3 cM). A genomic map of peach containing 83 RAPD, one isozyme, and four morphological markers was generated using an F2 family obtained by selfing an NC174RL x 'Pillar' F1. A total of 83 RAPD markers were assigned to 15 linkage groups. Various RAPD markers were linked to morphological traits. Bulked segregant analysis was used to identify RAPD markers flanking the red-leaf (Gr) and Mdh1 loci in the NC174RL x 'Pillar' and 'Marsun' x 'White Glory' F2 families, respectively. Three markers flanking Mdh1 and ten markers flanking Gr were identified. The combination of RAPD markers and bulked segregant analysis provides an efficient method of identifying markers flanking traits of interest. Markers linked to traits that can only be scored late in development are potentially useful for marker-aided selection in trees. Alternatives for obtaining additional map order information for repulsion-phase markers in large F2 populations are proposed.

Sweet cherry cultivar identification by leaf isozyme polymorphism

Isozyme polymorphism can assist in the identification of cherry cultivars. Ten isozymes, each showing variation at only one locus, provide 70 unique genotype profiles from leaf extracts of 78 different sweet cherry cultivars. Polymorphism in 6PGD, G6PD, GPI, IDH, PGM, FDP, SKDH and PER is demonstrated for the first time, while observations are extended for the previously described polymorphisms in MDH and GOT. Some cultivars with identical morphological characters and previously treated as one cultivar can be separated on the basis of isozyme genotype. Irradiated mutants and parent material could also be differentiated.