We analyzed the cytoplasmic diversity of CIP potato breeding germplasm. Cytoplasm types were assigned to 978 genotypes consisting of 265 foreign accessions used as input germplasm, 642 breeding lines developed by CIP, and 71 varieties released from CIP material. We found T (45 %), D (38 %), and W (11 %) to be the most frequent cytoplasm types in CIP breeding germplasm. Comparing the initial input germplasm to CIP breeding lines, the frequency of T-type cytoplasm decreased from 64 to 38 %, while those of D-and W-type cytoplasms increased from 26 to 41 % and from 6 to 14 %, respectively. We conclude that the CIP breeding program, as many others worldwide, has experienced a genetic bottleneck in terms of cytoplasmic diversity due to the unintended and continuous use of cytoplasmic-based male-sterile maternal lineages derived from Solanum demissum and S. stoloniferum in parental line and variety development. Nonetheless, the finding of male-fertile T-type breeding lines must have alleviated the problem to a certain extent, thus enabling CIP breeding progress.

No abstract

Dihaploid production from elite tetraploid cultivars is key to both traditional and novel breeding approaches that seek to simplify potato genetics. For this purpose, efficient and widely compatible haploid inducers (HIs) are needed. We compared PL-4, a new HI developed at the International Potato Center, to known HIs IvP101 and IvP35. By pollination of elite tetraploid breeding lines, we showed that PL-4 performed significantly better and had a homogeneous response regardless of the genetic background of the pistillate parents, on the most important efficiency traits—number of dihaploids per 100 fruits and haploid induction rate. Moreover, PL-4 exhibited a reduced proportion of hybrid seeds, a convenient trait for efficient screening. In this context, we recommend PL-4 as an enhanced HI for the potato breeding community.

Cytoplasmic male sterility (CMS) in potato is a common reproductive issue in late blight breeding programs since resistant sources usually have a wild cytoplasmic background (W or D). Nevertheless, in each breeding cycle male fertile lines have been observed within D- and T-type cytoplasms, indicating the presence of a fertility restorer (Rf) mechanism. Identifying sources of Rf and complete male sterility to implement a CMS–Rf system in potato is important since hybrid breeding is a feasible breeding strategy for potato. The objective of this study was to identify male fertile breeding lines and potential Rf candidate lines in the CIP late blight breeding pipeline. We characterized male fertility/sterility-related traits on 142 breeding lines of known cytoplasmic type. We found that pollen viability is not a reliable estimate of male sterility in diverse backgrounds. Breeding lines of the T-type cytoplasmic group had higher levels of male fertility than breeding lines of the D-type cytoplasmic group. With the help of pedigree records, reproductive traits evaluations and test crosses with female clones of diverse background, we identified four male parental lines segregating for Rf and three female parental lines that generated 100% male sterile progeny. These identified lines and generated test cross progenies will be valuable to develop validation populations for mitochondrial or nuclear markers for the CMS trait and for dihaploid generation of Rf+ lines that can be later employed in diploid hybrid breeding.

Improving potato late blight (LB) resistance is essential for ensuring food security, particularly using wild relatives endemic to Phytophthora infestans‐prone regions. However, reproductive barriers can impede the transfer from potato wild relatives (PWR) to the cultivated genepool. This study sought to incorporate potentially novel LB resistance from wild diploid accessions of Series Piurana (Solanum chiquidenum, Solanum paucissectum, and Solanum piurae), Tuberosa (Solanum cajamarquense), and Megistracroloba (Solanum sogarandinum) into tetraploid potato. Trough rescue pollination, 699 diploid interspecific hybrids were obtained, of which 385 displayed LB resistance in two endemic environments. Based on a comprehensive evaluation, including assessing 2n pollen production, 14 diploid interspecific hybrids were selected to continue the introgression process. These pre‐bred stocks were then used in interploidy (4x‐2x) crosses to incorporate their LB resistance in the cultivated tetraploid background. Assessment of 1978 genotypes resulting from interploidy crosses under endemic disease pressure yielded 717 hybrids with moderate to high levels of LB resistance. Evaluation of pollen viability and ploidy revealed moderate fertility and predominantly tetraploid genotypes. Reassessment of LB resistance on this new subset of hybrids further identified 214 genotypes with sustained resistance. Among them, 12 tetraploid hybrids with low glycoalkaloid content, favorable agronomic, and post‐harvest attributes were identified as crossing‐friendly stocks. Notably, 11 of these hybrids were derived from S. cajamarquense and one from S. sogarandinum. These promising 4x hybrids are now primed to be incorporated into potato breeding programs.