Lynda Hagen

Development and transferability of apricot and grape EST microsatellite markers across taxa

Abstract. EST microsatellite markers were developed in apricot (Prunus armeniaca L.) and grape (Vitis vinifera L.). cDNA libraries from either apricot leaves or grape roots were used in an enrichment procedure for GA and CA repeats. The transferability of EST simple sequence repeat (SSR) markers from apricot and grapevine to other related and unrelated species was examined. Overall, grape primers amplified products in most of the Vitaceae accessions while the apricot primers amplified polymorphic alleles only in closely related species of the Rosaceae. In this taxonomic family, ten EST SSR loci were tested, and one single primer pair, PacB22, was amplified across species and sections in the Prunoideae and Maloideae. Sequencing of EST SSR loci in other species and genera confirmed a higher level of conservation in the microsatellite motif and flanking regions in the Vitaceae compared to the Rosaceae. Two distinct fragments of the PacB22 locus amplified across the Malus and Pyrus genera; however, while the coding region was highly conserved, the microsatellite repeat motif was no longer present. The banding pattern was explained by base substitution and insertion/deletion events in the intronic region of PacB22. This study includes the determination of the degree of polymorphism detected among species and genera in two unrelated taxonomic families and the evaluation of the information provided by the microsatellite repeats and the flanking regions.

Molecular and Genetic Characterization of a Non-Climacteric Phenotype in Melon Reveals Two Loci Conferring Altered Ethylene Response in Fruit

Fruit ripening and abscission are associated with an ethylene burst in several melon (Cucumis melo) genotypes. In cantaloupe as in other climacteric fruit, exogenous ethylene can prematurely induce abscission, ethylene production, and ripening. Melon genotypes without fruit abscission or without ethylene burst also exist and are, therefore, non-climacteric. In the nonabscising melon fruit PI 161375, exogenous ethylene failed to stimulate abscission, loss of firmness, ethylene production, and expression of all target genes tested. However, the PI 161375 etiolated seedlings displayed the usual ethylene-induced triple response. Genetic analysis on a population of recombinant cantaloupe Charentais × PI 161375 inbred lines in segregation for fruit abscission and ethylene production indicated that both characters are controlled by two independent loci, abscission layer(Al)-3 and Al-4. The non-climacteric phenotype in fruit tissues is attributable to ethylene insensitivity conferred by the recessive allelic forms from PI 161375. Five candidate genes (two ACO, two ACS, and ERS) that were localized on the melon genetic map did not exhibit colocalization with Al-3 orAl-4.

Genetic control of fruit shape acts prior to anthesis in melon ( Cucumis melo L.).

Abstract. Genetic control of fruit shape in Cucumis melo was studied using QTL analysis in two Recombinant Inbred (RI) populations consisting of 163 and 63 individuals, respectively, obtained by crossing the same round-fruited parent with two different elongated-fruit lines. Fruit shape is mainly explained by fruit length in these two populations. Most QTLs for fruit shape and ovary shape detected were found to co-segregate, thus demonstrating early control of fruit shape during ovary development. A high level of correlation between fruit shape and ovary shape was also found in 14 unrelated genetic lines, a finding which suggests that control of fruit shape by gene(s) active early in the ovary is a general feature in C. melo. Two major flower genes, a (monoecious) and p (pentamerous), were shown to have major effects on fruit shape. Major tightly linked QTLs for fruit and ovary shape were found close to the a and p genes, probably reflecting their pleiotropic effect on fruit shape. Moreover, one of the two QTLs detected in the Védrantais × PI 414723 population was also found in the Védrantais × PI 161375 population. Variation of fruit shape in melon could be due to variations having quantitative effects on a large set of genes that are probably involved in ovary development.

Microsatellite markers in the hexaploid Prunus domestica species and parentage lineage of three European plum cultivars using nuclear and chloroplast simple-sequence repeats

In a previous study, cDNA microsatellite markers were described in apricot (Prunus armeniaca L.). Specific PCR primers were designed to amplify the microsatellite-containing regions from genomic DNA in different Prunus species. In the present work, cDNA microsatellite markers were developed in the hexaploid Prunus domestica L. species and polymorphism was ascertained in a segregating plum population. Co-dominant mendelian segregation of alleles was demonstrated and microsatellite polymorphism displayed up to 6 alleles per SSR locus per individual. Parentage lineage of three full-sib European plum cultivars (cv. ‘Cacanska najbolja’, ‘Cacanska rana’ and ‘Cacanska lepotica’) was reconstructed by the analysis of the above nuclear SSR markers, completed by four chloroplastic microsatellite loci. The six most informative nuclear loci enabled discrimination between the three Cacak cultivars and unrelated individuals as well as the previously proposed parents, ‘Wangenheim’ and ‘Pozegaca’. Data obtained support previous evidence that these cultivars originated from the ‘Stanley’ cultivar. However, SSR analysis finally excluded ‘Wangenheim’ as the other possible parent. Based on the results obtained with nuclear and chloroplast SSR loci, we propose the origin of those three Cacak cultivars in a cross between ‘Stanley’ as the mother plant and ‘Ruth gerstetter’ as the pollinator. Furthermore, we demonstrate the utility of these apricot SSR markers for genotype fingerprinting of the hexaploid plum cultivars.