Ultrastructural and histochemical features of pistil of Malus communis: The stylar transmitting tissue

The structural and histochemical features of the stylar transmitting tissue of Malus communis were investigated by light and transmission electron microscopy. The transmitting tissue of apple is composed of cells and intercellular substance. The cells are very rich in cytoplasm and are characterized by numerous large rough endoplasmic reticulum (RER) cisterns, and by large Golgi vesicles rich in polysaccharides. The intercellular substance, probably secreted by transmitting tissue cells, contains proteins and polysaccharides. A possible role of the intercellular substance in the incompatibility reaction is discussed.     

Role of the genes Md-ACO1 and Md-ACS1 in ethylene production and shelf life of apple (Malus domestica Borkh)

Shelf life determines the economic life time of mature apples, which can be either freshly harvested or stored. Good shelf life is highly associated with a slow decrease of fruit firmness at room temperature. Apple is a climacteric fruit, in which loss of firmness seems to be physiologically related to ethylene. Ethylenes biosynthetic pathway is controlled by two large gene families coding for 1-aminocyclopropane-1-carboxylate synthase (ACS) and 1-aminocyclopropane-1-carboxylate oxydase (ACO).In this study, one ACS and one ACO gene were examined for their effect on ethylene production and shelf life in apple using gene specific molecular marker, and have also been positioned on a molecular marker linkage map. The ACO marker was developed in this research and mapped on linkage group (LG) 10 of the crosses Prima × Fiesta and Fuji × Mondial Gala, within the 5% border of a previously identified fruit firmness QTL [Theor Appl Genet 100 (2000) 1074]. We denoted this locus as Md-ACO1. In addition, we mapped the previously developed Md-ACS1 marker [Theor Appl Genet 101 (2000) 742] on LG15.Studies on the cross Fuji × Braeburn revealed that Md-ACS1 and Md-ACO1 independently affect the internal ethylene concentration (IEC) as well as shelf life of apple, Md-ACS1 having the strongest effect. Descendants homozygous for Md-ACS1-2 and Md-ACO1-1 showed to have the lowest ethylene production as well as superior shelf-life. These two genes are candidates to be included in marker assisted breeding.     

Effect of CPPU on fruit and shoot growth of apple

The effects of CPPU on the growth of fruits and bourse shoots of apple were examined by targeted applications of 20 mg I“1 CPPU to fruitlets and/or bourse-shoot and spur leaves. Treating fruitlets and fruitlets-plus-leaves stimulated fruit growth to a similar extent; fruit growth rate was temporarily suppressed when only the leaves were treated. Conversely, bourse shoot growth was stimulated by leaf and leaf-plus-fruit treatments. All CPPU applications reduced the content of fruit soluble solids and induced a paler yellowish- green fruit ground colour.     

Effect of Succinic Acid 2,2-Dimethyl Hydrazide on Flowering and Gibberellic Acid Contents of Sweet Cherry (Prunus Avium L.)

Applications of Alar to young sweet cherry trees for two successive seasons promoted flower bud formation. The starch content of the treated branches was higher than that of the control shoots, but the lignin contents were equal except in the terminal part. Stem diameter was increased by the treatment, but neither the average transverse diameter of the xylem cells nor their wall thickness was measurably changed. While causing a reduction in diffusible GA from apices of upright shoots, Alar did not affect the amount which diffused from horizontal or laterally oriented shoot apices. The amounts of diffusible and extractable gibberellin-like substances from the apices of upright shoots decreased with time; Alar treatment accentuated the decrease.     

The inheritance of the red colour character in European pear (Pyrus communis) and its map position in the mutated cultivar ‘Max Red Bartlett’

The inheritance of the red colour character in European pear (Pyrus communis L.) was studied over 3 years in seven progeny obtained by using the cultivars ‘Max Red Bartlett’, ‘Cascade’ and ‘California’ as red‐skinned fruit parental lines. One of these progeny (derived from the cross ‘Abbé Fétel’ × ‘Max Red Bartlett’, a red mutation of ‘Bartlett’) was already used to construct two linkage maps and, being ‘red colour’ a monogenic dominant trait, it was possible to locate it as morphological marker in the linkage group 4 of ‘Max Red Bartlett’. For the first time, this trait has been mapped out of linkage group 9 in a species belonging to the Maloideae subfamily moreover in a mutated sport. An improved knowledge of the genetic basis of production and accumulation of red pigments in the fruit skin will better support the pear breeding programmes aimed to select new cultivars carrying this appealing trait.     

The ‘European Apple Genome Mapping Project’-developing a strategy for mapping genes coding for agronomic characters in tree species

Summary A recently initiated collaborative project involving apple breeders in seven European countries is described. The objective is to improve the European apple crop by molecular-aided breeding to increase efficency and reduce the time-scale in breeding for resistance, tree habit and fruit quality. The strategy adopted provides a model for similar studies in fruit, forest and other woody species. The project is based on progenies from a small number of crosses involving many important agronomic genes. Replication of these reference progenies by vegetative propagation will enable studies to be carried out simultaneously in each country. By developing a range of molecular markers, including isozymes, RFLPs and sequence-tagged DNA probes, an integrated molecular map is being constructed for use in a wide range of breeding and genetic studies. Construction of a database recording many mapped molecular markers will enable efficient exploitation of data in future genetic, breeding and physiological studies of apple. Aspects of the adopted strategy, techniques and management are discussed in the context of mapping genes in perennial crop genomes.     

Isolation of two microsatellite markers from BAC clones of the Vf scab resistance region and molecular characterization of scab‐resistant accessions in Malus germplasm*

A polymerase chain reaction (PCR)‐based method was developed to isolate microsatellite markers from large‐insert genomic DNA clones of bacterial artificial chromosome (BAC) libraries. The method is fast and economic since it does not require subcloning. It was applied to isolate a microsatellite marker from a BAC clone of the chromosomal region containing the apple scab resistance gene Vf. The Vf gene of Malus floribunda 821 is the most widely used source of scab resistance in apple breeding. A second microsatellite was found on the extremity of a BAC clone flanking the Vf locus. The two microsatellites allowed the identification of the presence of the Vf gene in the scab‐resistant accessions M. micromalus SA573‐3, ‘Golden Gem’, M. prunifolia 19651 and MA 16 not previously known to carry this gene. They were also used to verify the correctness of the published genealogical tree of the Vf cultivar ‘Florina’, in which a probable mistake was identified. This analysis shows the importance of genotyping the Vf locus when choosing scab‐resistant germplasm as parents in breeding programmes.     

Development of reliable PCR markers for the selection of the Vf gene conferring scab resistance in apple

Early selection of scab-resistant apple seedlings can be enhanced by the use of markers tightly linked to the Vf resistance gene. Two sequence characterized amplified regions (SCAR) markers have been obtained from previously described random amplified polymorphic DNA (RAPD) markers. AM19-SCAR is a codominant marker, while AM19-SCAR is dominant, as is the RAPD from which it was derived. A highly detailed map in the vicinity of the Vf gene was built through the cumulative analysis of about 600 seedlings from six different controlled crosses. The usefulness of these and other SCAR markers will be discussed in relation to combining the traditional phenotypic selection with MAS. The availability of two codominant, tightly linked markers flanking both sides of the resistance gene (AL07-SCAR and M18-CAPS) also makes it easy to identify the seedlings homozygous for the resistance gene.