Development of a rapid identification method for potato cytoplasm and its use for evaluating Japanese collections

The cytoplasm of potatoes, characterized by the presence of T-type chloroplast DNA and β-type mitochondrial DNA, is sensitive to nuclear chromosomal genes that contribute to various types of male sterility. Past breeding efforts with various potato varieties have resulted in several different cytoplasms other than T/β. Varieties with Solanum stoloniferum-derived cytoplasm (W/γ) show complete male sterility, while those with S. demissum-derived cytoplasm (W/α) produce abundant, but non-functional pollen. Thus, identification of cytoplasmic types is important for designing efficient mating combinations. To date, only T-type chloroplast DNA can be accurately identified by a PCR marker. Here, we report a rapid identification technique by multiplex PCR, followed by restriction digestion with BamHI in one reaction tube, and propose a new nomenclature for potato cytoplasm types (T, D, P, A, M, and W). Using this new technique, our collections of 748 genotypes, including 84 Japanese named varieties, 378 breeding lines and 26 landraces, and 260 foreign varieties and breeding lines, were grouped into cytoplasm types: T (73.9 %), D (17.4 %), P (4.5 %), A (1.5 %), M (0.3 %), and W (2.4 %). The utility of this marker system for breeding is discussed.