Abstract
Male sterility in potato is little studied since traditional breeding is based on the vegetative reproduction of highly heterozygous tetraploid varieties. The rapid development of hybrid diploid breeding contributes to growing interest in studying the male sterility of this important crop. In this work, a set of 6 cytoplasmic markers was employed to describe cytoplasmic genetic diversity of 185 potato cultivars bred in Russia and FSU countries. Three cytoplasm types were identified, T (40.0 %), D (50.8 %) and W/ γ (8.7 %), which according to literature are associated with male sterility. With a single exception (0.5 %), cytoplasm types characteristic of male fertile forms (A, P) were not found in the subset of 185 cultivars. A comparison of these results with previously published data suggested expanding the subset to up to 277 cultivars, all developed in Russia or FSU countries; however, the resulting differentiation into three cytoplasm types (T, D and W/ γ ) was nearly the same. Fertility phenotyping helped identify both male-sterile and male-fertile genotypes within the three groups of varieties with T-, D- and W/ γ -type cytoplasm. Fifteen genotypes differing in cytoplasm type and male sterility/fertility traits were selected for direct sequencing of 8 mtDNA loci. Fragments of the nad2, nad7, cox2, atp6 and CcmFc genes were identical in all 15 selected genotypes. The polymorphism, detected in the rps3, atp9 and CcmFc loci, was not associated with male sterility. Two SNPs in the nad1/atp6 and nad2 loci differentiated 7 genotypes with W/ γ -type cytoplasm into five genotypes with tetrad sterility, and two with fertile pollen. The results of an NGS analysis confirmed the association of these SNPs with tetrad sterility in a larger set of 28 genotypes of different origin, all with W/ γ -type cytoplasm. A heteroplasmy state was observed both in male-sterile and in male-fertile genotypes.
Highlights
In more than 300 years, covering the breeding history of potato (Solanum tuberosum) outside South America, where it was domesticated, thousands of cultivars have been developed by breeders; they are presently cultivated in nearly 150 countries
Identification of cytoplasm types in potato varieties Types of cytoplasm were identified in 185 improved potato cultivars, and the resulting data are presented in the Table and Fig. 2
In the remaining 184 cultivars, the BamHI restriction site was detected in the PCR product of SAC primers, they may be counted among the varieties with Т, D- and W/γ- types of cytoplasm, which are associated with the male sterility traits according to Hosaka and Sanetomo (2012)
Summary
In more than 300 years, covering the breeding history of potato (Solanum tuberosum) outside South America, where it was domesticated, thousands of cultivars have been developed by breeders; they are presently cultivated in nearly 150 countries This 300-year period may be divided into three stages: (1) the breeding process of the 18th–19th centuries, based on a restricted genetic diversity of relatively not numerous South America’s indigenous cultivars introduced to Europe; (2) beginning from the early 20th century, targeted crossing of cultivated potato with wild species in order to introgress R genes, first of all, conferring resistance to fungal and viral pathogens; and (3) the third phase that we are standing witness to is marked by the emergence of essentially novel trends in potato breeding: cysgenesis, genome editing, and diploid hybrid breeding. Those challenges have had not been so relevant, so far as the conventional potato production is based on vegetative reproduction of highly heterozygous tetraploid cultivars
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