Simple Sequence Repeat Characterisation of Traditional Apple Cultivars (Malus domestica Borkh.) Grown in the Region of Madrid (Central Spain)

Abstract

The genetic diversity of many Spanish apple collections has been evaluated, but some areas from Central Spain have not been included. In the present work, a set of 41 accessions (33 diploids and 8 triploids) of 23 traditional apple cultivars collected in the region of Madrid and maintained at the IMIDRA collection was analysed with 13 simple sequence repeats (SSRs) to evaluate its diversity. Three reference cultivars (‘Fuji’, ‘Granny Smith’ and ‘Reineta Gris’) were included as reference to align the SSR profiles. The average number of alleles per locus was 7.66, which increased to 8.75 with triploids, and the number of rare alleles was 36. Moreover, the observed heterozygosity (Ho) was 0.74 and the expected heterozygosity (He) was 0.66, indicating disequilibrium. The probability to find two identical individuals was very low (PID = 3.60 × 10−12). After the cluster analysis, 29% of the accessions were found to have redundant profiles. Principal coordinate analysis, clustering and Bayesian model suggested the presence of four well-defined subgroups in the diploid of traditional apple. In clustering, diploid reference cultivars were nested with triploids independently from diploid traditional cultivars. Finally, after comparing profiles and names with other traditional Spanish cultivars, we conclude that the following studied collection shares the ubiquitous accessions from cultivar groups, such as «camuesas», «peros» and ‘Reineta’ but contains novel and uncharacterised cultivars with potential opportunities in breeding programmes and rural development: ‘Agridulce’, ‘Amarillo de El Paular’, ‘Hojancas’, ‘Mailla blanca’, ‘Pepita de melon’ and ‘Rabudas’. As these cultivars were collected in such a small area with environmental distinctiveness, they constitute a singular germplasm reservoir, which deserves to be preserved and more deeply studied.