Biological diversity in Malus sieversii populations from Central Asia

Malus sieversii is the main ancestor of the cultivated apple (M. domestica) and is mainly endangered in its center of diversity in Kazakstan. Seeds from 35 wild Malus sieversii across 7 locations (1089 seedlings in total) were selected and germinated for evaluation at the fruit genebank at Dresden-Pillnitz. The seeds were supplied by the USDA-ARS Plant Genetic Resources Unit, Geneva, NY, USA, which obtained them during expeditions to Central Asia. The assessment of the genetic diversity of these seedlings should give assistance in preserving (in situ) the original habitats and for further collecting strategies. The main practical objective of this research is to find new sources of disease resistances and improved horticultural qualities for breeding new apple varieties. The broad range of variability within the plant material can already be observed after 2 to 3 years of evaluation (e.g. start and length of the vegetation period, plant height). Evaluations of apple scab and powdery mildew symptoms, caused by natural infections, showed significant differences within and between offsprings. A total of 64 individuals showed complete absence of both diseases. Therefore, new sources of resistance for use in breeding programs are expected to be identified. With regard to apple scab, this assumption was supported by initial PCR experiments employing closely linked SCAR and RAPD markers for the Vf -gene. Neither of 21 preselected M. sieversii individuals from 6 different sites displayed the respective marker bands, although being scored resistant to the disease. In PCR analyses aimed at determining the genetic diversity of 26 M. sieversii individuals from the different populations, a very good correlation between genetic similarity and the origin of the different individuals could be observed. The evaluation of this material and its characterization by molecular markers is planned to be intensified in future years.