Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 3/8/2010
Publication Date: N/A
Interpretive Summary: The diversity within wild and cultivated apple species has not previously been described. In this chapter, we present summaries of fruit weight, fruit color, and fire blight resistance for diverse apple species. We demonstrate that the cultivated species, Malus x domestica, and potential progenitor species M. sylvestris and M. sieversii have a higher percentage of accessions with large fruit than the wild apple species. We select two wild apple species. M. orientalis and M. sieversii to show that genetic differentiation among locations is similar for both species and that variation is more strongly partitioned among maternal lines than geographic regions.
Technical Abstract: Biodiversity serves as the basis for all selective improvement for agricultural traits. Understanding this variation among domesticated and wild species is critical for future gene discovery research. The USDA-ARS-National Plant Germplasm System maintains 52 different species of Malus, of which only Malus x domestica is cultivated. A comparison of fruit weight among Malus species reveals that M. x domestica has the highest number of large fruited accessions in the collection, while putative progenitor species M. sylvestris and M. sieversii have larger fruit than many of the other wild species. Fruit color varies widely across species and some wild species of Malus have remarkably high proportions of accessions with resistance to fire blight (Erwinia amylovora). The genetic diversity among accessions representing wild populations of M. orientalis (from Russia, Turkey, Armenia and Georgia) and M. sieversii (from Kazkahstan) was similar between the two species. The differentiation among sites was between 0.05 and 0.09 and the differentiation among families was between 0.19 and 0.21, revealing that variation is more strongly partitioned among maternal lines than geographic regions.