Nitrogen Use Efficiency in Diploid Potato of the Phureja Group: A Novel Insight

Nitrogen is an essential nutrient for plants, used by farmers to increase the yield of crops. However, this practice increases greenhouse gases, negatively affecting the environment. Nitrogen Use Efficiency (NUE) is a trait that is beginning to be studied in some model species and in cereals due to its complex and novel trait nature. In potatoes, the information is limited. Therefore, this research can help to mitigate the environmental impact of nitrogen fertilizer use, reducing groundwater contamination and greenhouse gas emissions. The study of NUE at the genetic level, based on a diverse population in potato materials, will contribute to the understanding of the genetic architecture of the trait. This research evaluated NUE in a Solanum tuberosum diploid potato genetic diversity panel from the Phureja group. The characterization of the trait was carried out in substrate conditions, for low and high levels of nitrogen for both the vegetative and the reproductive phase. Eighteen variables associated with NUE were measured, nine under low nitrogen and nine under high nitrogen conditions. A GWAS was conducted, and a total of 21 QTNs were identified as strongly associated with 11 phenotypic variables related to NUE in potato, these QTNs explained between 0.08% and 2.7% of the observed phenotypic variation, along with a repertoire of 750 candidate genes associated with the trait. This research aimed to establish the basis for understanding the genetic architecture of NUE in Solanum tuberosum. Once the candidate genes are validated, they could be used to develop molecular tools and accelerate breeding programs aimed at improving NUE in Solanum tuberosum.

Developing N use efficient potato varieties requires exploring the genetic basis of nitrogen use efficiency (NUE) and associated agronomic and physiological traits. In order to identify QTLs for NUE and NUE-related traits, and to determine the relationships between the traits and QTLs in potato, a diploid potato mapping population (CxE) was evaluated in the field in Ethiopia under low and high N fertilizer levels. QTL detection was performed using interval mapping and multiple QTL mapping (MQM). A total of 52 putative QTLs were identified for ten traits, of which 28 QTLs were detected under low N availability while the remaining 24 QTLs were detected under high N conditions. Several QTLs were location and N level specific, suggesting the presence of QTL x environment interaction. A region on linkage group V (21-38 cM) accumulated the largest number of QTLs. This region coincides with the earliness locus encoded by the CDF1 gene, suggesting that earliness has a profound influence on NUE. A putative second QTL region on linkage group V located 20 cM from the earliness locus (38-56 cM) and a region on linkage group IV (60-72 cM) might be useful other regions to focus on, for NUE improvement in potato. To verify the stability of the identified QTLs and to use these for the detection of possible candidate genes, further multi-environment trials with larger population size may be required.

Potato is a prime food security crop for smallholder farmers in the highland part of North western Ethiopia. In this region, nutrient availability, especially nitrogen (N) is a major constraint for crop productivity. To obtain insight in the possibility of improving potato for growth under low N input conditions in Ethiopia, we evaluated CxE diploid back cross population, modern European and Ethiopian potato cultivars and local Ethiopian cultivars for their ability to grow and produce tubers under low and high N input conditions. The experiments were conducted under rainfed and irrigation conditions. Eighty-eight Dutch cultivars and 9 Ethiopian cultivars were evaluated in three locations in North-western Ethiopia, in 2013 and in 2015. The two years represent two different growth seasons: rain-fed (June-October 2013) and irrigated cultivation (February-June 2015). Similarly 100 CxE diploid back cross potato genotypes were evaluated in both rainfed and irrigation production seasons in 2014. The Growth of the plants was monitored throughout the growth cycle using canopy cover measurements, with modelled canopy characteristics, and other agronomic traits were measured as per the description. The effect of season and location was further investigated by a GGE Biplot genotype-by-environment interaction analysis, and genetic factors determining phenotypic traits and yield were identified through QTL mapping and association mapping. Ethiopian cultivars showed a remarkable, environment-dependent difference in utilisation of the canopy for tuber production. While total photosynthetic capacity was higher in Ethiopian cultivars than in Dutch cultivars in rainfed production season at Injibara, tuber production was higher in Dutch cultivars. This low radiation use efficiency was not observed in the other rain-fed location (Debre-Tabor). A Genotype by Environment analysis using GGE biplots demonstrates that, Irrespective of the N levels and locations, rainfed production season test environments were grouped as one mega environment and irrigation production season test environments as the other mega environment, indicating most of the variation for yield and nitrogen use efficiency (NUE) in the dataset may be caused by the effect of rain-fed vs irrigation season. Further trials are needed to confirm this result. The QTL mapping with the CxE diploid population and GWAS analysis with the Dutch cultivars discovered both season-environment and N-specific QTL as well as constitutive QTLs. Overall, N availability affects Dutch and Ethiopian cultivars differentially, with strong environmental interaction on canopy and yield traits. Rainfed and irrigated seasons in Ethiopia may require different breeding programs for improved yield under varying fertilizer levels. Both constitutive and environment-specific QTLs were identified that may be targets for breeding prorgams towards improved yield under Ethiopian cultivation conditions.

Considerable effort has been made to develop management practices to reduce environmental losses of nitrogen (N) from potato production systems. Increasing the efficiency of N utilization by the potato crop is one approach to reducing environmental losses of N. This study evaluated the variation in N use efficiency characteristics of a series of superior Andigena and diploid potato selections from two populations of potato germplasm selected for adaptation to long days within the potato breeding program of Agriculture and Agri-Food Canada. Seven Andigena selections (six in 2001), seven diploid selections and two commercial cultivars (Kennebec, Butte) were grown at two fertilizer N rates (0 or 100 kg N ha−1) in 2000 and 2001. Plant dry matter and N accumulation were measured on one date chosen to reflect the onset of senescence. Drought conditions in 2001 reduced tuber yield and crop response to N fertilization compared with 2000. Significant variation in N use efficiency characteristics were measured among selections in both years. Variation in N utilization efficiency (plant dry matter accumulation/plant N accumulation) among selections was consistent across the 2 years of this study, despite dramatically different environmental conditions. With the exception of selection 12581-06, N use efficiency parameters for the commercial cultivars was generally similar to or superior to that for the Andigena and diploid selections. Nitrogen use efficiency (plant dry matter accumulation/crop N supply) was generally increased for selections with less visible evidence of senescence at the time of plant sampling, and for selections that partitioned a greater proportion of plant N to vines. The significant variation in N use efficiency characteristics, and the consistent pattern of these N use efficiency characteristics among selections across contrasting environmental conditions, suggest that it is practical to screen adapted potato germplasm with respect to N use efficiency characteristics.

ABSTRACTThe south of Colombia is a center of diversity for diploid potatoes in the Solanum tuberosum group Phureja. This germplasm is important for genetic studies and is used as a genetic resource in potato breeding programs. In Andean countries, Phureja group potatoes are a staple food and represent important incomes for smallholder farmers. We studied the genetic diversity and population structure of 110 diploid potato group Phureja accessions by analyzing allele frequencies using a set of 42 microsatellites (simple sequence repeats). The accessions used in this study were 97 diploid S. tuberosum Phureja group accessions from the Colombian Core Collection and 13 diploid accessions from the German germplasm bank. Allelic richness, heterozygosity, population differentiation (F statistics) and population allocation by means of Bayesian modeling analyses were performed. Results indicated that the population is highly diverse (Hs = 0.55), and genetic differentiation (FST = 0.09636) is mainly due to differences between accessions (FIS = 0.17115). These indexes of population differentiation suggest a moderate division within the population but not a marked population structure. Results with respect to the genetic structure of the analyzed germplasm provide the basis for the development and implementation of linkage and association mapping as well as methods for precision breeding such as the search for diagnostic molecular markers.

The tuber dormancy is an important aspect of tuber’s physiological age and begins with tuber initiation. It is largely dependent on genotype, environmental conditions, and tuber age. The group Phureja among diploid potatoes, has a very short or no tuber dormancy while the tubers of Solanum jamesii, a wild potato species, may remain dormant for more than eight years and have the tendency to sprout in favourable conditions. The dormancy breakage in potato is accompanied by many physiological changes such as changes in the ratios of abscisic acid (ABA)/ cytokinin and ABA/ gibberellic acid (GA3), catalase inhibition and accumulation of soluble sugars. These all changes are interlinked and occur in the same time frame. The dormant buds have 77% of their nuclei in the growth phase (G1), compared to only 13% in the preparation phase for mitosis (G2), resulting in slower development of active buds. This paper reviews various factors involved in natural and forced dormancy breakage of potato tuber in relation to their use as seed potatoes immediately after harvesting and implementation of different exogenous dormancy breaking methods like cold pre-treatment, growth regulators, electric current and irradiation to induce sprouting in potatoes.

Resistance to late blight in potato is either qualitative or quantitative in nature. The quantitative resistance is durable, but the molecular and biochemical mechanisms underlying quantitative resistance are poorly understood, and are not efficiently utilised in potato breeding. A non-targeted metabolomics, using high resolution hybrid mass spectrometry, was applied to decipher the mechanisms of resistance in the advanced breeding diploid potato genotypes (Solanum tuberosum L. Group Phureja), with valuable sources of genetic diversity. The metabolomics profiles of resistant genotypes (AC04 and AC09) were compared with a susceptible commercial genotype (Criolla Colombia), following Phytophthora infestans or mock-inoculation, to identify the resistance related (RR) metabolites. Metabolites belonging to phenylpropanoids, flavonoid and alkaloid chemical groups were highly induced in resistant genotypes relative to susceptible. Concurrently, the biosynthetic genes, tyrosine decarboxylase (TyDC) and tyramine hydroxycinnamoyl transferase (THT), involved in the biosynthesis of hydroxycinnamic acid amides (HCAAs), and chalcone synthase (CHS) and flavonol synthase (FLS), involved in flavonoid biosynthesis, were also upregulated, as confirmed by quantitative real-time PCR. Probable genes coding for these enzymes were sequenced and nonsynonymous single-nucleotide polymorphisms (nsSNPs) were identified. The resistance to late blight observed in this study was mainly associated with cell wall thickening due to deposition of HCAAs, flavonoids and alkaloids.

Genetic variance components for tuber dormancy in an interpopulation hybrid betweenSolanum tuberosum (Group Phureja) and (Group Stenotomum) were estimated using a N.C. Design II mating plan. The genetic variance estimate was high and was composed entirely of additive variance. The estimate of narrow sense heritability was. 73. The results indicated that significant progress can be made in shifting the mean length of tuber dormancy by simple mass selection techniques.

The diploid yellow potato (Solanum tuberosum L. Phureja Group) is an important plant genetic resource. In this study, we report for the first time the characterization of anther development and pollen formation in the cultivar Criolla Colombia. The description of morphological and histological characters of buds and flowers at different developmental stages permitted to identify ten main stages, from the differentiation of the male cells of the sporangium, meiosis, microspores formation and maturation, to the release of mature pollen. In addition, the results provide a graphic guide of the development of the anther, through the sequential and orderly formation of the epidermis, the endothecium, the middle layer and the nutritive layer or tapetum. This microanatomical information will be useful for work focused on androgenesis and identification of gene regulation in floral biology and gamete formation. Therefore, this study determined that to efficiently obtain haploids, flower buds between 5 and 8.9 mm long (stage 6 to 8) should be used, in which tetrads and microspores are in the early uninucleate and binucleate stage.

Water availability is one of the main limitations of potato yields due to the high sensitivity of this crop to water deficit. The objective of this study was to determine the effect of water deficit on some physiological and biochemical responses in yellow diploid potato plants (Solanum tuberosum L. Group Phureja) of the cultivars Criolla Colombia, Criolla Dorada and Criolla Ocarina. Plants at tuber initiation were subjected to two treatments: continuous irrigation and water deficit imposed by withholding water at tuber initiation for 17 d. The results showed that plants under water deficit increased chlorophyll concentration, malondialdehyde and proline content. However, these plants showed a decrease in stomatal conductance, leafarea, total dry mass and exhibited a higher root/shoot ratio in all potato cultivars. In addition, all the cultivars also showed a decrease in yield, which was associated with sensitivity to water stress. Although the high content of proline and high root/shoot ratio may be associated with tolerance to water deficit, this association was not observed in these cultivars, probably due to the high reduction of stomatal conductance, which limited the production of photoassimilates, plant growth, and,therefore, the yield.

The photoperiodic behaviour of 18 potato clones from three taxonomic groups (Andigena, Phureja, and Tuberosum diploid and tetraploid) was studied under controlled environments. Day lengths of 11, 13, 15, and 17 hours were provided with all other environmental conditions common. Six characters were studied: tuber formation, stem height, haulm weight, tuber number, tuber weight, and tuberization efficiency (tuber weight/haulm weight).

The effects of inbreeding in cultivated diploid potatoes were studied by using self-fertile hybrids from crosses between Group Phureja and Group Stenotomum and haploids of Group Tuberosum. S1, S2 and S3 progenies usually exhibited decreased performance and vigour with increased inbreeding. In most families the inbreeding depression seemed to coincide with a curve claculated on the basis of the expected loss of heterozygosity in a diploid organism. The performance of some progenies deviated markedly from expectations apparently because a non-random sample of parents contributed to later generations. Many inbred genotypes were lost owing to poor seedling vigour or tuberization. This indicated the presence of many harmful recessive genes. The rapid increase in homozygosity following selfing at the diploid level provides a means for developing homozygous clones with a potential for use in future genetic investigations.

Foliar applications of boron (B) constitute a frequent practice in the fertilization of the yellow diploid potato and are generally done with excessive and empirical doses generating toxicities in crops. The effect of foliar applications of B at doses of 0, 0.5, 1.2, or 4 kg ha-1 was determined for physiological and metabolic variables and toxicity symptoms in the yellow diploid potato cultivar Criolla Galeras under greenhouse conditions using Na octaborate (20.5% B, 11% Na) or boric acid (17.5% B) as sources of B. Significant differences (P<0.05) were found between the sources and doses for dry matter (DW), leaf area (LA), proline content, and electrolyte leakage (ECh). The highest toxicity was observed for B applied as sodium octaborate at concentrations of 2 and 4 kg ha-1 B with a reduction of DM up to 40%, a decrease of LA up to 90%, a loss of 60% in ECh, and a significant increase in the concentration of proline (65 μmol/g fresh weight). The lower toxicity of boric acid at doses higher than 2 kg ha-1 B indicated that the octaborate Na presented synergism with B, which can result in a greater oxidative stress, causing instability of the membranes, necrosis and premature tissue death, as evidenced in the description of the visual symptoms. The doses of 0.5 and 1.0 kg ha-1 B for both sources resulted in positive responses in the DW and non-significant (P<0.05) differences with the control, associated with the levels of proline and ECh, which indicated a narrow range between the deficiency and toxicity of B for cv. Criolla Galeras, where the effect of the accompanying ion must be considered in the selection of the boron source.

The Solanum tuberosum L. Phureja Group consists of potato landraces widely grown in the Andes from western Venezuela to central Bolivia, and forms an important breeding stock due to their excellent culinary properties and other traits for developing modern varieties. They have been distinguished by short-day adaptation, diploid ploidy (2n = 2x = 24), and lack of tuber dormancy. This nuclear simple sequence repeat (nSSR or microsatellite) study complements a prior random amplified polymorphic DNA (RAPD) study to explore the use of these markers to form a core collection of cultivar groups of potatoes. Like this prior RAPD study, we analyzed 128 accessions of the Phureja Group using nuclear microsatellites (nSSR). Twenty-six of the 128 accessions were invariant for 22 nSSR markers assayed. The nSSR data uncovered 25 unexpected triploid and tetraploid accessions. Chromosome counts of the 102 accessions confirmed these nSSR results and highlighted seven more triploids or tetraploids. Thus, these nSSR markers (except 1) are good indicators of ploidy for diploid potatoes in 92% of the cases. The nSSR and RAPD results: (1) were highly discordant for the remaining 70 accessions that were diploid and variable in nSSR, (2) show the utility of nSSRs to effectively uncover many ploidy variants in cultivated potato, (3) support the use of a cultivar-group (rather than a species) classification of cultivated potato, (4) fail to support a relationship between genetic distance and geographic distance, (5) question the use of any single type of molecular marker to construct core collections.

Phureja Group potato is endemic and important for northern Andean countries such as Colombia, Ecuador and Venezuela, where it is grown over a wide range of elevation. The objective of the study was to compare the biomass accumulation of five potato cultivars in three contrasting environments in elevation from a latent response variable of vector nature, analogous to “heat efficiency index”. Destructive samplings were carried to obtain biomass. A biomass accumulation model was proposed using a latent response variable that integrates total biomass per plant with thermal time, analogous to the “heat use efficiency index”. The proposed latent response variable allowed measuring the efficiency in biomass accumulation and making comparisons between elevations and cultivars, with a nonparametric longitudinal variance analysis. The middle location was where the highest efficiency in accumulation of total biomass was observed. The accumulation of total biomass was slow at the higher elevation location during the vegetative stage, but it increased considerably after the initiation of the growth of tubers. The study showed a clear genotype-environment interaction, suggesting that biomass accumulation changes with elevation according to the cultivar. The methodology used in this study has the potential to be used in the longitudinal comparison of cultivars and environments, even when variations in elevation or temperature alter the length of growing cycles.