¹Genetic analysis of red pigmentation in ‘bon rouge’ pears (Pyrus communis L.)
European pear (Pyrus communis L.) is the third most important fruit in South Africa after citrus and apple. The Agricultural Research Council (ARC) breeding programme seeks to obtain a fully red coloured pear. Sports (mutants) with red skin and reddish leaves of various cultivars occur and some have been used in breeding programmes, where they transmit red colour as a single gene. The red trait in ‘Max Red Bartlett’, a mutant of ‘Bartlett’ (Synonym – ‘Williams Bon Chretien’), was mapped in Italy to linkage group 4 (LG4). At ARC Infruitec-Nietvoorbij, Stellenbosch, South Africa, ‘Bon Rouge’ pear, another red mutant of ‘Williams Bon Chretien’, was crossed with ‘Packham’s Triumph’ generating an F1 population with a segregation of (54:71) red:green, approximating to a 1:1 ratio; indicating a simple Mendelian inheritance of the red trait. The aim of the study was to determine if the ‘Bon Rouge’ red colour trait maps to approximately the same position as the ‘Max Red Bartlett’ red colour trait on LG4, and if so, to identify SSR markers that are mapped closer to the red colour trait than were previously reported. The seven published pear and apple SSR markers mapped in the appropriate region of LG4 in pear and in apple maps were identified and screened in the parents and, where informative, were scored in 125 seedlings for co-segregation analysis. Single locus segregations were checked with JoinMap 4.1 and this program was also used to generate a genetic map for LG4 of the ‘Bon Rouge’ x ‘Packham’s Triumph’ progeny using the SSR markers and the red locus. Two linkage maps were constructed at a LOD threshold of 3 using the Kosambi mapping function, one each with the maximum likelihood and regression mapping algorithms. The genetic linkage map of LG4 of ‘Bon Rouge’ x ‘Packham’s Triumph’ consisted of seven SSR markers (2 from apple and 5 from pear). Markers CH01d03 and CH02c02b were mapped on the same position as the red trait in ‘Max Red Bartlett’ reported by Dondini et al. (2008) and four more markers were added. One of the newly mapped markers, NH011a has been found to be closely linked to the red trait, with an approximate distance of 4 cM. This marker can be used to indirectly select for the red gene in pear, for example to distinguish heterozygotes from homozygotes. This work sets the scene for further genetic studies on the red trait in pear breeding programmes.