European pear (Pyrus communis L.) is among the important fruit species for which only few genetic studies have been carried out. Available evidence indicates that simple sequence repeats (SSR) are very useful as molecular markers because they are codominant, highly polymorphic, abundant and reproducible. The present paper reports more than 100 apple SSR markers in two populations of European pear; a total of 41 SSR markers were then positioned on a genetic linkage map of the cross 'Passe Crassane' x 'Harrow Sweet' and 31 in the map 'Abbe Fetel' x 'Max Red Bartlett'. Syntenic relationships between pear and apple maps have been considered for the chromosomes carrying two or more SSR markers. The alignment among the two maps supports the colinearity of the two genomes with respect both to identification and to orientation of the linkage groups.

Pear scab caused by Venturia pyrina is an economically important disease throughout the world and can cause severe crop loss in susceptible cultivars. The varying range of susceptibility to pear scab in F1 populations has made it possible to identify quantitative trait loci (QTLs). Ninety-five seedlings derived from the cross 'Abbè Fétel' (AF)×'Max Red Bartlett' (MRB) were evaluated for scab resistance in greenhouse tests, with 39% being classified as resistant, 33 as moderately susceptible and 28 as highly susceptible. Amplified fragment length polymorphisms (157) and simple sequence repeats (41) were used to construct two maps, one of 908.1 cM (AF) and the other of 879.8 cM (MRB). The analysis of the resistance data collected made it possible to identify two major QTLs on linkage groups 3 and 7 associated with resistance to V. pyrina. Both QTLs explained 88% of the phenotypic variance and the log of odds values were higher than 10, suggesting the involvement of two major genes in pear scab resistance.

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 ÔMax Red BartlettÕ, ÔCascadeÕ and ÔCaliforniaÕ as red-skinned fruit parental lines. One of these progeny (derived from the cross ÔAbbe´Fe´telÕ · ÔMax Red BartlettÕ, a red mutation of ÔBartlettÕ) was already used to construct two linkage maps and, being Ôred colourÕ a monogenic dominant trait, it was possible to locate it as morphological marker in the linkage group 4 of ÔMax Red BartlettÕ. 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.

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BACKGROUND:The scab, which is caused by Venturia nashicola, gives serious damages to pear trees. 'Niitaka'