Rodrigo Nicolao

Hybridization is a powerful process in plant evolution generating reticulate patterns of speciation, introgression, and chloroplast capture. In the Petota clade of Solanum, which spans cultivated and wild potatoes, these processes cause much of the taxonomic complexity of the group. We examined the evolutionary history of the Commersoniana group (Solanum commersonii and S. malmeanum) relative to S. chacoense (Tuberosa Group) using an integrative framework of phylogenomics and morphology. With target-capture sequencing (Angiosperms353) of nuclear and plastid loci recovered from herbarium specimens, together with data mining we built nuclear and plastome phylogenies and ran symmetry tests, gene concordance analyses, and coalescent simulations to weigh incomplete lineage sorting against chloroplast capture. The data reveal cytonuclear discordance and events consistent with chloroplast capture from S. chacoense into Commersoniana lineages supported by both empirical and simulated results. Phylogenetic networks confirm repeated historical and recent reticulation, especially involving S. malmeanum. Non-metric Multidimensional Scaling (NMDS) of morphological traits did not recover clear species boundaries but was consistent with a hybrid origin for the group. These results indicate that recurrent hybridization and event consistent with chloroplast capture are strongly influencing evolution in the examined wild potatoes, complicating classical taxonomy and informing conservation and breeding. They also underscore the value of combining genomic and phenotypic data to resolve species boundaries in plant groups with tangled hybrid histories.

Solanum malmeanum , a wild relative of the potato ( S. tuberosum ), is native to Argentina, Brazil, Paraguay and Uruguay. This wild potato species belongs to the tertiary gene pool (2 x = 2 n = 24, 1EBN – Endosperm Balance Number) and possesses valuable traits for potato breeding. Understanding its reproductive mechanisms is crucial for effectively utilizing potato wild relatives in breeding programs. Five accessions of S. malmeanum , conserved at the Embrapa Clima Temperado Potato Genebank, were evaluated to assess their reproductive behaviour and determine whether the production of viable seeds from self‐pollination results from successful fertilization or apomixis. Pollen size was measured, and viability was assessed using microscopy. Five treatments involving controlled crosses were made to evaluate gametes compatibility, response to self‐pollination, occurrence of parthenocarpy and/or apomixis, and the presence of autogamy and allogamy. Pollen viability ranged from 96% to 100%, with viable pollen measuring 20 μm to 22 μm in diameter. Cross‐pollinations confirmed that all accessions produced viable male and female gametes and were allogamous. No accession produced parthenocarpic fruit or apomictic seeds. Four self‐pollinated accessions were self‐incompatible, resulting in no fruit and seeds. Self‐incompatibility was attributed to a pre‐zygotic barrier, with pollen tube growth inhibited at 1/3 of the style length in accession BRA 00183778‐0 and 2/3 in accessions BRA 00167071‐0, BRA 00167093‐4 and BRA 00183754‐1. One self‐pollinated accession (BRA 00183755‐8) produced three fruits resulting in 51 seeds. From these, 17 germinated, and 16 of the resulting seedlings tuberized, confirming self‐compatibility. This study identified one S. malmeanum accession (BRA 00183755‐8) as a new source of genetic variability for inbred‐hybrid potato breeding. Further investigations are needed to elucidate the mechanism underlying self‐compatibility, such as the role of the S‐locus inhibitor ( Sli ) gene, or potential malfunction of S‐RNase or HT genes.

Wild potato relatives are vital for breeding programs to tackle rising temperatures. This study proposes a methodological approach based on the examination of genetic variation among 19 accessions belonging to Solanum chacoense and Solanum commersonii from the Embrapa Potato Genebank under heat stress (HS). Heat tolerance coefficient (HTC) was calculated using genotypic values predicted through mixed models. After 15 days of heat stress (DHS), a significant variation in gas exchange and chlorophyll fluorescence indicates strong breeding potential and photosystem resilience. By 35 DHS, increased pigment variation suggests acclimation. Based on predicted genotypic values, S. chacoense outperforms S. commersonii in tuber production and gas exchange under HS, and principal component analysis (PCA) performed using the HTC shows early resistance driven by photosynthesis, mid-term by tuber yield, and long-term by gas exchange and tuber production. Genotypes BRA00167017-3, BRA00167023-1, BRA00167025-6, and BRA00167028-0 excel in heat comprehensive evaluation values (HCEVs)/comprehensive principal component value (F) rankings, demonstrating robust photosynthesis, thermoregulation, and tuber yield. Cluster analysis identifies these as highly tolerant, ideal for breeding heat-resilient potatoes. These PCA-derived weights and genotype clustering system provide a precise tool for selecting heat-tolerant wild potato germplasm, categorizing them into highly tolerant, moderately tolerant, sensitive with late recovery, and highly sensitive groups acquired for specific objectives of the breeding programs to climate change.

Screening of pollen traits in diploid wild potatoes (Solanum sect. Petota, Solanaceae) is desirable to develop heat-tolerant potato (S. tuberosum) cultivars. To accomplish this goal requires exploring potato genetic resources that are conserved in genebanks. The goal of this study was to assess pollen viability and 2n pollen production of the diploid potato wild relatives under heat stress condition. We assessed pollen viability and size of nine potato accessions conserved at the Embrapa Potato Gene Bank, including eight wild potatoes S. chacoense (BRA 00167447-2, BRA 00167017-3, BRA 00167023-1, BRA 00167028-0), S. commersonii (BRA00167007-4, BRA00167420-9, BRA00183760-8), and S. malmeanum (BRA 00183755-8), along with a control accession from the cultivated species S. tuberosum (BRA 00167251-8). The plant accessions were cultivated in different growth chambers, subjected to both control temperature (ranging from 14 to 27°C) and supraoptimal temperature conditions (ranging from 24 to 34°C). At heat stress, the accessions BRA 00167251-8 did not bloom, and BRA 00167023-1 did not produce pollen. The remaining accessions did not exhibit a significant reduction in pollen viability as the temperature increased. Pollen viability at the control temperature had the lowest value in BRA-00167420-9 (S. commersonii) with 68.5% and the highest in BRA 00183755-8 (S. malmeanum) with 100%. At the supraoptimal temperature the lowest value was in BRA 00167420-9 (S. commersonii) with 54.5% and the highest in BRA 00167017-3 (S. chacoense) with 94%. The average of pollen diameter was 20 μm in all wild potato genotypes, and the increase of temperature did not lead to 2n pollen production. Estimated Genotypic Coefficient of Variation (GCV) was lower than Phenotypic Coefficient of Variation (PCV) for pollen viability. The observed heritability values ranged from 58.82% in BRA00167007-4 to 91.32% in BRA 00183755-8. Our results highlight the genetic variability available in wild potato germplasm concerning pollen viability under heat stress. Furthermore, these first insights offer valuable guidance for ongoing and future endeavors in diploid potato breeding.

F1 hybrid potato breeding at the diploid level requires the development of new inbred lines from self-compatible germplasm. This study was carried out to search for new sources of self-compatible diploid wild potatoes focusing on the 1EBN species Solanum malmeanum. Five diploid accessions from Embrapa potato genebank were screened to evaluate their reproductive behavior and check if the production of viable seeds when self-pollinated results from successful fertilizations or apomixis. Measurements of the pollen were taken, and pollen viability was evaluated. Five treatments based on controlled crosses assessed gametes compatibility; response to self-pollination; occurrence of parthenocarpy and/or apomixis; and tested the accessions for autogamy and allogamy. Pollen viability vary from 96% to 100%, with viable pollen size varying from 20 µm to 22 µm. Cross-pollinations confirmed that all accessions produced viable gametes and are allogamous, since pollen tube growth confirmed fertilization in treatments where seeds were set. No accession produced parthenocarpic fruit nor apomictic seeds. Four self-pollinated accessions were self-incompatible with no fruit and seeds set. Self-incompatibility was due to a pre-zygotic barrier confirmed by inhibited pollen tube growth at 1/3 style length in BRA 00183778-0 and 2/3 in BRA 00167071-0, BRA 00167093-4, and BRA 00183754-1. One self-pollinated accession (BRA 00183755-8) produced 3 fruits totalizing 51 seeds. The self-compatibility in this accession was confirmed based on the image record of pollen tubes reaching the ovules, thus rejecting apomixis, which also did not occur in control (non-manipulated bagged flowers) and emasculated bagged flowers. The 51 endogamic seeds obtained were sown, and 17 seedlings were obtained, from which 16 tuberized. Still, further investigations are needed to elucidate the mechanism responsible for the self-compatibility, such as S-locus inhibitor (Sli), malfunction of S-RNase or HT genes.

Heat stress is one of the major factors reducing potato yield by limiting the plant photosynthesis activity, production and partitioning of assimilates to the sink. Potato wild relatives (Solanum sect. Petota) are a natural reservoir of valuable traits for abiotic stress resistance. However, it is necessary to assess the response of wild potato genotypes based on physiological features such as gas exchange, chlorophyll index and chlorophyll fluorescence that are promising candidates to improve crop photosynthesis under adverse conditions. Multivariate approaches on two factor experimental design were used to select the best performing genotypes for most important traits influencing the photosynthetic activity under control and heat stress treatments. The most important traits to be focused on are net photosynthetic rates, transpiration rates, and stomatal conductance along with effective photochemical yield of PSII, Coefficient of photochemical yield of PSII, electron transport rate and Fv/Fm ratio which are highly associated with heat stress conditions. Solanum commersonii accessions (BGB003, BGB009) are more likely to be tolerant to heat stress, followed by S. tuberosum 2x (BGB091, BGB093) and S. chacoense (BGB101). The assessment of wild accessions for photosynthetic traits under heat stress is a reliable way to discriminate the most promising sources of abiotic stress resistance even though they have unreliable tuber traits for the breeding of the potato crop.

Crop wild relatives are gaining increasing attention. Their use in plant breeding is essential to broaden the genetic basis of crops as well as to meet industrial demands, for global food security and sustainable production. Solanum malmeanum (Solanum sect. Petota, Solanaceae) is a wild relative of potatoes (S. tuberosum) from Southern South America, occurring in Argentina, Brazil, Paraguay and Uruguay. This wild potato has been largely mistaken for or historically considered as conspecific with S. commersonii. Recently, it was reinstated at the species level. Retrieving information on its traits and applied uses is challenging, because the species name has not always been applied correctly and also because species circumscriptions and morphological criteria applied to recognize it have not been consistent. To overcome these difficulties, we performed a thorough literature reference survey, herbaria specimens’ identification revision and genebank database queries to review and update the information available on this potato wild relative, contributing to an increase in research on it to fully understand and explore its potential for potato breeding. Scarce studies have been carried out concerning its reproductive biology, resistance against pests and diseases as well as tolerance to abiotic stresses and evaluation of quality traits. The scattered information available makes it less represented in genebanks and genetic studies are missing. We compile, update and present available information for S. malmeanum on taxonomy, geographical distribution, ecology, reproductive biology, relationship with its closest relatives, biotic and abiotic stresses resistance and quality traits and discuss ways to overcome sexual barriers of hybridization and future perspectives for its use in potato breeding. As a final remark, we highlight that this species’ potential uses have been neglected and must be unlocked. Thus, further studies on morphological and genetic variability with molecular tools are fundamental for an efficient conservation and applied use of this promising genetic resource.