Early Tuber Research Articles

Early Tuberization: A Heat Stress Escape Strategy in the Fresh Market Potato Variety Vanguard Russet

Early Tuberization: A Heat Stress Escape Strategy in the Fresh Market Potato Variety Vanguard Russet

Yield reduction caused by elevated temperatures and high nitrogen fertilization is mitigated by SP6A overexpression in potato (Solanum tuberosum L.).

Potatoes (Solanum tuberosum L.) are a fundamental staple for millions of people worldwide. They provide essential amino acids, vitamins, and starch - a vital component of the human diet, providing energy and serving as a source of fiber. Unfortunately, global warming is posing a severe threat to this crop, leading to significant yield losses, and thereby endangering global food security. Industrial agriculture traditionally relies on excessive nitrogen (N) fertilization to boost yields. However, it remains uncertain whether this is effective in combating heat-related yield losses of potato. Therefore, our study aimed to investigate the combinatory effects of heat stress and N fertilization on potato tuber formation. We demonstrate that N levels and heat significantly impact tuber development. The combination of high N and heat delays tuberization, while N deficiency initiates early tuberization, likely through starvation-induced signals, independent of SELF-PRUNING 6A (SP6A), a critical regulator of tuberization. We also found that high N levels in combination with heat reduce tuber yield rather than improve it. However, our study revealed that SP6A overexpression can promote tuberization under these inhibiting conditions. By utilizing the excess of N for accumulating tuber biomass, SP6A overexpressing plants exhibit a shift in biomass distribution towards the tubers. This results in an increased yield compared to wild-type plants. Our results highlight the role of SP6A overexpression as a viable strategy for ensuring stable potato yields in the face of global warming. As such, our findings provide insights into the complex factors impacting potato crop productivity.

Cytokinin application improving growth, sugar content, polyphenol and flavonoid content in Yacon tuberous roots

Yacon is a tuberous crop that accumulates sugar in large quantities and has many valuable secondary compounds in medicine such as phenolic compounds and flavonoids. The objective of this study was to increase the size and content of sugars, polyphenols and flavonoids during the early growth of tubers. Therefore, early tuber stimulation and tuber size are important as they determine yield over time. Cell restructuring along with growth expansion as well as control of tuber reserves also takes place. This study investigated anatomy structure changes, fresh weight, dry weight, respiratory intensity and sugar content in different Yacon root types. A spray of N-benzyl adenine (BA) (0–25 ppm) is applied in the initial stage. Determining agronomic, physiological, and, biochemical indicators after 4 weeks of treatment, the sugar content of tubers determines the yield of tubers after 16 weeks of treatment. The results showed that Yacon crops at the stages of 5 to 9 weeks develop fibrous roots, thin fibrous roots and pre-tuberous roots at week 13, intermediate storage roots at week 17 and mature storage roots at week 17. BA 20 ppm application on Yacon crop week 13 increased the number of storage roots, fresh weight, dry weight tuber diameter, total sugar content, fructan content, total phenolic and flavonoid remarkably compared to controls, but reducing sugar content is lower than treating BA at 15 ppm. BA 20 ppm application on Yacon crop week 13 increased the parameters of sugar growth and accumulation, tuber yeild on a plant increased 2 times, dry weight increased 1.65 times, sugar content, total sugar 1.12 times, reducing sugar 3.01 times, fructan 1.36 times, total phenolic and flavonoid 1.36 and 1.26 times after 25 weeks of treatment.

Cell-Free Supernatant (CFS) from Bacillus subtilis EB2004S and Lactobacillus helveticus EL2006H Cultured at a Range of pH Levels Modulates Potato Plant Growth under Greenhouse Conditions.

Agriculture involving industrial fertilizers is another major human made contributing factor to soil pH variation after natural factors such as soil parent rock, weathering time span, climate, and vegetation. The current study assessed the potential effect of cell-free supernatant (CFS) obtained from Bacillus subtilis EB2004S and Lactobacillus helveticus EL2006H cultured at three pH levels (5, 7, and 8) on potato (var Goldrush) growth enhancement in a greenhouse pot experiment. The results showed that CFSs obtained from B. subtilis EB2004S and L. helveticus EL2006H cultured at pH 5 significantly improved photosynthetic rates, stomatal conductance, root fresh weight, and whole plant fresh weight. interactive effects of pot pH and that of CFSs obtained from pH 5 influenced chlorophyll, plant height, and shoot and whole plant fresh weight. Moreover, treatment 52EB2004S~0.4% initiated early tuberization for potato grown at pH 7 and 8. Potato grown at pH 5, which received a 72EB2004S~0.4% CFS treatment, had greater whole plant fresh and dry weight than that treated with L. helveticus EL2006H CFS and a positive control. Taken together, the findings of this study are unique in that it probed the effect of CFS produced under differing pH conditions which revealed a new possibility to mitigate stresses in plants.

Melatonin Mitigates Drought Induced Oxidative Stress in Potato Plants through Modulation of Osmolytes, Sugar Metabolism, ABA Homeostasis and Antioxidant Enzymes.

The effect of melatonin (MT) on potato plants under drought stress is still unclear in the available literature. Here, we studied the effect of MT as a foliar application at 0, 0.05, 0.1, and 0.2 mM on potato plants grown under well-watered and drought stressed conditions during the most critical period of early tuberization stage. The results indicated that under drought stress conditions, exogenous MT significantly (p ≤ 0.05) improved shoot fresh weight, shoot dry weight, chlorophyll (Chl; a, b and a + b), leaf relative water content (RWC), free amino acids (FAA), non-reducing sugars, total soluble sugars, cell membrane stability index, superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (G-POX), and ascorbate peroxidase (APX) compared to the untreated plants. Meanwhile, carotenoids, proline, methylglyoxal (MG), H2O2, lipid peroxidation (malondialdehyde; MDA) and abscisic acid (ABA) were significantly decreased compared to the untreated plants. These responses may reveal the protective role of MT against drought induced carbonyl/oxidative stress and enhancing the antioxidative defense systems. Furthermore, tuber yield was differentially responded to MT treatments under well-watered and drought stressed conditions. Since, applied-MT led to an obvious decrease in tuber yield under well-watered conditions. In contrast, under drought conditions, tuber yield was substantially increased by MT-treatments up to 0.1 mM. These results may imply that under water deficiency, MT can regulate the tuberization process in potato plants by hindering ABA transport from the root to shoot system, on the one hand, and by increasing the non-reducing sugars on the other hand.

Synthesis of biocompatible Fe3O4 and MnO2 nanoparticles for enhanced tuberization in potato (Solanum tuberosum L.)

Iron oxide (Fe3O4) and manganese dioxide (MnO2) Nanoparticles (NPs) were synthesized via green synthesis approach using beetroot (Beta vulgaris) leaf extract and evaluated as nanofertilizer for studies of In-vitro microtuberization of potato. Successfully biogenesis of NPs were demonstrated through UV–visible spectroscopy, FTIR, XRD, SEM-EDX, and TEM analysis. In-vitro micortuberization analysis, single nodal explants of potato were placed on media (Murashige-Skoog plant growth medium devoid of original Fe and Mn salt) added with different concentrations of metal oxide-NPs, and physiological, biochemical and molecular changes were observed via using standard methods. The interaction of the NPs with the nodal explants significantly induced early tuber induction and tuber growth upon application of Fe3O4NPs (4.0 mg L-1) and MnO2NPs (1.0 mg L-1) in comparison to untreated potato tissues. Molecular analysis of potato tissues revealed enhanced expression of primary tuber inducing genes viz. Calcium-Dependent Protein Kinases (StCDPK), Calmodulin (StCaM1), and Lipoxygenase (StLOX) enzyme activity show a positive correlation of tuber induction with added NPs. Further elemental analysis via EDX exhibited that the addition of biocompatible metal oxide NPs in the growth media induced the cytosolic Ca+2 burst leading to enhanced expression of major tuber induction pathway genes resulting in early and enhanced potato tuberization. Absorption of metal-oxide NPs in microtubers was evaluated by FTIR and EDX mapping. This study is the first report on the molecular mechanism involved in regulating NPs induced the potato tuberization under In-vitro conditions. The study also indicated that application of the metal-oxide NPs as nano-nutrient to enhanced potato microtuber production.

Resistance to Phytophthora infestans Clonal Lineage US-23 in Potato Cultivars and Its Relationship with Early Blight Resistance and Tuber Yield.

Resistance to late blight caused by Phytophthora infestans clonal lineage US-23 in 217 old and modern potato cultivars was evaluated in field trials in 2016 and 2017 in Pennsylvania. Significant differences in resistance were found among these cultivars (P < 0.0001). Significant interaction between cultivars and environments was found (P < 0.0001). The values of relative area under the disease progress curve ranged from 0 to 0.5841 in 2016 and from 0 to 0.5469 in 2017. Broad-sense heritability of late blight resistance was estimated to be 0.91, with a 95% confidence interval of 0.88 to 0.93. Cluster analysis classified the cultivars into five groups: resistant, moderately resistant, intermediate, moderately susceptible, and susceptible. Thirty cultivars showing resistance and 32 cultivars showing moderate resistance were identified. The 217 cultivars were also evaluated for foliar maturity, tuber yield, and resistance to early blight caused by Alternaria solani. A few cultivars with late blight resistance independent of late maturity were found. Late blight resistance and early blight resistance were positively correlated, and 17 cultivars possessed resistance to both diseases. Yield trade-off associated with late blight resistance was not observed among the cultivars in the absence of disease pressure.

Genes related to circadian rhythm are involved in regulating tuberization time in potato

Early tuberization, a short period from stolon occurrence to tuber formation, is one of the major characteristics of a good early-maturing potato cultivar, while the regulatory mechanism of tuberization time (TT) is still unclear. In this study, two tetraploid cultivars, Zhongshu 3 (Z3) and Zhongshu 18 (Z18), with short and long TT respectively, were examined to reveal regulatory genes related to TT using RNA sequencing of tissue samples taken during stolon occurrence, stolon swelling and tuber formation. Cluster analysis showed that the gene expression patterns at the stolon swelling and tuber formation stages were significantly different from those at stolon occurrence in both Z3 and Z18. Therefore, we screened the differentially expressed genes (DEGs) at stolon swelling and tuber formation and compared them to those at stolon occurrence. A total of 3 085 DEGs were specifically identified and analyzed according to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment, and DEGs involved in starch and sucrose metabolism, plant hormone signal transduction and plant circadian clock were significantly enriched. The circadian clock genes were significantly differentially expressed between Z3 and Z18, revealing an important role for the plant circadian pathway in regulating TT. Furthermore, three candidate genes, StGI, StPRR and StEFM involved in circadian regulation and significantly differentially expressed between Z3 and Z18, were discovered and confirmed by qRT-PCR. The results provide valuable information for understanding the regulatory mechanisms of potato TT and represent a step toward breeding early-maturing potato cultivars.

Phenology-Adjusted Stress Severity Index to Assess Genotypic Responses to Terminal Drought in Field Grown Potato

Potato is a drought susceptible, often rain-fed crop suffering strongly from even short periods of soil water deficit. With global environmental conditions changing, potato clones resistant to variable water supply are needed and identifying them is a major task. Many indices assessing potato tolerance to water deficit have been proposed, albeit none of them takes into account the severity of the stress or the sensitivity of the developmental stage during which the stress occurs. As a result, data obtained on genotypes in one location or season are normally not useful in another location or in a different season. We have developed an index evaluating yield response of potato to water deficit based on the soil tension the genotype was subjected to for the duration of the stress modified by the development stage of the genotype. The sum of the daily values was combined in a stress severity index (SSI). In total thirteen genotypes differing in duration and sensitivity to drought were subjected to four levels of deficit irrigation on two soil types at different development stages over two years. Early drought (early tuber filling) reduced yields up to 95% whereas late drought (late tuber bulking) reduced yields significantly less. SSI depended on the genotypic phenological development and on the soil tension values and ranges between 25 and 3500. The index differentiated genotypic responses well across treatments and soil types, even with these relatively advanced development stages, up to a value of 1000. Beyond 1000, yields were generally reduced by more than 60% and a differentiation between genotypes was not possible anymore. SSI constitutes a method that renders site, location, year, season, and soil type effects comparable for responses of potato clones to soil water deficit. Combining this measure of stress severity with other proposed indices may improve upon their current weaknesses in finding or identifying the underlying traits of drought tolerance in potato.

Air Injection of Subsurface Drip Irrigation Water Improves Tuber Yield and Quality of Russet Potato

Irrigation water for potato production is becoming an issue in most irrigated production regions. Producing potatoes under drip irrigation has proven to reduce irrigation water use. However, tuber productivity has to increase under drip irrigation to offset the initial cost of installing the drip system. Ambient aeration of drip irrigation water may improve tuber yield and quality. A field study was conducted at Colorado State University’s San Luis Valley Research Center, Colorado, USA, to evaluate the effect of ambient air injection of subsurface drip irrigation water on leaf growth and tuber performance of potato cultivar Rio Grande Russet. Treatments included aerated and non-aerated drip irrigated plots that were randomly assigned within four replicated blocks. The Mazzei Venturi system was inserted in the main drip line to inject ambient air into drip tapes that supplied aerated water to the air injected treatment plots. Plants that received aerated drip irrigation water produced higher total tuber yield and increased the yield of large marketable size (> 170 g and > 285 g) tubers compared to plants grown under non-aerated drip irrigation water. The yield increases were, 8%, 19%, and 5%, for total, > 170 g, and > 285 g tuber yield, respectively. Early tuber bulking was observed, Leaf Area Index increased, and root mass production increased in plants that received aerated drip irrigation water compared to plants that received non-aerated irrigation water. Tuber external defects (growth cracks, knobs, and misshapes) were reduced by 9.2% in tubers produced under aerated drip irrigation water. Data from this study clearly indicate that ambient air injection of subsurface drip irrigation water can improve potato productivity and tuber quality. AJPR-D-20–00030R1.

Radiation Interception, Conversion and Partitioning Efficiency in Potato Landraces: How Far Are We from the Optimum?

Crop efficiencies associated with intercepted radiation, conversion into biomass and allocation to edible organs are essential for yield improvement strategies that would enhance genetic properties to maximize carbon gain without increasing crop inputs. The production of 20 potato landraces—never studied before—was analyzed for radiation interception (), conversion () and partitioning () efficiencies. Additionally, other physiological traits related to senescence delay (normalized difference vegetation index (NDVI)), tuberization precocity (), photosynthetic performance and dry tuber yield per plant (TY) were also assessed. Vegetation reflectance was remotely acquired and the efficiencies estimated through a process-based model parameterized by a time-series of airborne imageries. The combination of and , closely associated with an early tuber maturity and a NDVI explained 39% of the variability grouping the most productive genotypes. TY was closely correlated to senescence delay (r = 0.74), indicating the usefulness of remote sensing methods for potato yield diversity characterization. About 89% of TY was explained by the first three principal components, associated mainly to , and , respectively. When comparing potato with other major crops, its is very close to the theoretical maximum. These findings suggest that there is room for improving and to enhance potato production.

Elevated temperature and carbon dioxide alter resource allocation to growth, storage and defence in cassava (Manihot esculenta)

Rising atmospheric CO2 concentrations and global warming can alter how plants partition their resources. This is important for food crops through changes in resource allocation to edible tissues and toxic defence compounds. While research suggests elevated temperature and [CO2] independently drive changes in plant metabolism and stress levels, and photosynthetic rates, respectively, it is less clear how these environmental changes impact plants when combined. Cassava is an important dietary staple for many developing nations. However, the safety of cassava depends on cyanogenic glucoside concentrations. In a climate-controlled greenhouse, the effects of elevated temperature in the presence and absence of elevated [CO2] on the growth, physiology and chemical defence of cassava at two growth stages were examined. Growth in cassava was initially increased by elevated temperature. However, across time, simultaneous elevated [CO2] led to an increasing biomass advantage over plants grown at ambient [CO2] and temperature. Elevated temperature and [CO2] also significantly increased tuber initiation and early tuber expansion. Tuber and leaf cyanide concentrations were significantly reduced under elevated temperature, while elevated temperature and [CO2] produced tuber cyanide concentrations similar to the higher levels found in plants grown at ambient conditions. The findings highlight how future climate change may impact both cassava production and quality.

Post-transcriptional Regulation of FLOWERING LOCUS T Modulates Heat-Dependent Source-Sink Development in Potato

Understanding tuberization in the major crop plant potato (Solanum tuberosum L.) is of importance to secure yield even under changing environmental conditions. Tuber formation is controlled by a homolog of the floral inductor FLOWERING LOCUS T, referred to as SP6A. To gain deeper insights into its function, we created transgenic potato plants overexpressing a codon-optimized version of SP6A, SP6Acop, to avoid silencing effects. These plants exhibited extremely early tuberization at the juvenile stage, hindering green biomass development and indicating a tremendous shift in the source sink balance. The meristem identity was altered in dormant buds of transgenic tubers. This strong phenotype, not being reported so far for plants overexpressing an unmodified SP6A, could be due to post-transcriptional regulation. In fact, a putative SP6A-specific small regulatory RNA was identified in potato. It was effectively repressing SP6A mRNA accumulation in transient assays as well as in leaves of young potato plants prior to tuber formation. SP6A expression is downregulated under heat, preventing tuberization. The molecular mechanism has not been elucidated yet. We showed that this small RNA is strongly upregulated under heat. The importance of the small RNA was demonstrated by overexpression of a target mimicry construct, which led to an increased SP6A expression, enabling tuberization even under continuous heat conditions, which abolished tuber formation in the wild-type. Thus, our study describes an additional regulatory mechanism for SP6A besides the well-known pathway that integrates both developmental and environmental signals to control tuberization and is therefore apromising target for breeding of heat-tolerant potato.

Differential Mechanisms of Potato Yield Loss Induced by High Day and Night Temperatures During Tuber Initiation and Bulking: Photosynthesis and Tuber Growth.

The tuber yield of potatoes is vulnerable to high temperature and is challenged by the asymmetric increase in day and night temperatures. This study aimed to evaluate photosynthesis, biomass growth, tuber mass distribution, and dry tuber yield in early harvested potatoes that were field-grown under high day and night temperature conditions during different growth stages. Potatoes were exposed to ambient (control), high night temperature (HNT; 19:00–7:00), high day temperature (HDT; 7:00–19:00), and high day/night temperature (HDNT; all day) for 14 days during tuber initiation (TI) or tuber bulking (TB) using portable, temperature-controlled plastic houses that were controlled to increase the temperature by 4.0°C. During TI, HNT delayed tuber development, thus altering tuber mass distribution by reducing the yield proportion of large tubers of >100 g (-53.7%) and lowering early harvest index (-16.1%), causing a significant yield loss (-17.2%) without interfering with photosynthesis. In contrast, HDT decreased early tuber yield (-18.1%) by reducing photosynthetic sources, which was probably attributed to decreased photosynthetic efficiency through a feedback inhibition. However, HDT altered neither tuber mass distribution nor early harvest index. HDNT during TI exhibited all the aforementioned effects of HNT and HDT (i.e., cumulative effects): reduced yield proportion of large tubers (-46.7%), decreased early harvest index (-23.7%), and reduced photosynthetic rate; thus, HDNT caused the highest yield loss (-30.3%). During TB, when the tubers were fully developed, the thermal effects decreased because most of the effects were either directly or indirectly linked to tuber development. These results provide comprehensive insight to the differential mechanisms of potato yield loss under high day and night temperatures and show that further field experiments should be conducted to cope with the threat of global warming on potato production.

What makes turnips: anatomy, physiology and transcriptome during early stages of its hypocotyl-tuber development

Brassica species are characterized by their tremendous intraspecific diversity, exemplified by leafy vegetables, oilseeds, and crops with enlarged inflorescences or above ground storage organs. In contrast to potato tubers that are edible storage organs storing energy as starch and are the vegetative propagation modules, the storage organs of turnips, grown from true seed, are swollen hypocotyls with varying degrees of root and stem that mainly store glucose and fructose. To highlight their anatomical origin, we use the term “hypocotyl-tuber” for these turnip vegetative storage organs. We combined cytological, physiological, genetic and transcriptomic approaches, aiming to identify the initial stages, molecular pathways and regulatory genes for hypocotyl-tuber induction in turnips (B. rapa subsp. rapa). We first studied the development of the hypocotyl zone of turnip and Pak choi and found that 16 days after sowing (DAS) morphological changes occurred in the xylem which indicated the early tuberization stage. Tissue culture experiments showed a clear effect of auxin on hypocotyl-tuber growth. Differentially expressed genes between 1 and 6 weeks after sowing in turnip hypocotyls, located in genomic regions involved in tuber initiation and/or tuber growth defined by QTL and selective sweeps for tuber formation, were identified as candidate genes that were studied in more detail for their role in hypocotyl-tuber formation. This included a Bra-FLOR1 paralogue with increased expression 16 DAS, when the hypocotyl starts swelling, suggesting dual roles for duplicated flowering time genes in flowering and hypocotyl-tuber induction. Bra-CYP735A2 was identified for its possible role in tuber growth via trans-zeatin. Weigthed Co-expression Network Analysis (WGCNA) identified 59 modules of co-expressed genes. Bra-FLOR1 and Bra-CYP735A2 were grouped in a module that included several genes involved in carbohydrate transport and metabolism, cell-wall growth, auxin regulation and secondary metabolism that serve as starting points to illuminate the transcriptional regulation of hypocotyl-tuber formation and development.

The effects of different concentration of sucrose and various auxin on in vitro shoot and microtuber formation of red potato (Solanum tuberosum, L. var Desiree)

The experiment was aims to study the effect of different sucrose concentrations (30, 90, 120 and 150 g.L−1) and various types of auxin (IAA, IBA, NAA) on in vitro shoot and microtuber formation of Red Potato (Solanum tuberosum, L. var Desiree). Young stem cutting from planlet cultured on half strength MS medium. All types of auxin use the concentration of 0.25 mg.L−1. The research conducted a completely randomized design (CRD) factorial. The data obtained were analyzed by analysis of variance (ANOVA) and DMRT test at 0.05. Parameters observed included growth of microtuber and shoot growth, such as number of shoots and shoot length. The observations result for 3 months, show that the higher the concentration of sucrose, can stimulate tuber formation but suppress shoot growth. Early tuber initiation (36,7 DAP) and optimum number of tuber was observed in 150 g.L−1 sucrose, whereas at 30g.L−1 had no effect to tuber induction. In addition, high number of microtuber was observed in NAA compare to other auxin. Observational data on shoot growth showed that the higher concentration of sucrose will inhibit bud formation. The 90 g.L−1 sucrose concentration showed the best number of shoots, which averaged 1.5 shoots/plantlet. But at a concentration of 30g/L sucrose, explants are only able to form callus. In the bud length parameter, IAA gave the best response that is an average of 3cm/shoot.

ВЛИЯНИЕ ГУСТОТЫ ПОСАДКИ КЛУБНЕЙ КАРТОФЕЛЯ НА УРОЖАЙНОСТЬ, СТРУКТУРУ УРОЖАЯ, КАЧЕСТВО ПРОДУКЦИИ И ТОВАРНОСТЬ КЛУБНЕЙ

The article deals with the influence of planting depth of potato tubers on productivity, structure, quality of products and the marketability of potato crop in the conditions of the Chuvash Republic. The depth of seeding of tubers has a direct impact on all processes of growth and development. The more favorable the complex of conditions in the zone of placement of planted tubers, the faster they germinate and give early and amicable shoots, the more successful the further development of the potato plant and the formation of the crop. Determining the dependence of the potato tuber planting depth on the productivity, structure, quality of the products and the marketability of potato plants hinders many causes that are directly related to the growth and development of potato plants, as the productivity of potato plants is significantly increased by optimizing the priority conditions that are necessary in potato cultivation, when there is an increase in all indicators of photosynthetic activity of potato plants. The density of plants should be such that plants could form a powerful leaf surface, a root system and make the best use of solar energy and soil nutrients [11 12]. In numerous studies by our and foreign authors on the definition of optimal areas of potato nutrition, the following general provisions are present: late varieties, that develop a powerful top, are placed less often, early - thicker; the less moisture in the soil, the less should be the density of planting [6]. In this study, in order to determine potato productivity, we first of all determined crop yields, structure, product quality and marketability of tubers. Norms of planting can be determined depending on the density of the stalk. The high density of plant standings promotes acceleration of passage of development phases by plants, early tuber formation and ripening of a potato [3,4,5,7,8,9]. Thus, in the experiments, carried out by V.T. Spiridonov (1972) in the Chuvash Agricultural Institute in the variant where the planting was carried out according to the scheme of 70x30 cm, the entry of plants into the mass flowering phase was noted 2-3 days earlier than when planting according to the scheme of 70x35 cm. Reduction of the distance between tubers to 25 cm accelerated the development of plants 5 days.

Genome-Wide Identification, Expression, and Functional Analysis of the Sugar Transporter Gene Family in Cassava (Manihot esculenta).

The sugar transporter (STP) gene family encodes monosaccharide transporters that contain 12 transmembrane domains and belong to the major facilitator superfamily. STP genes play critical roles in monosaccharide distribution and participate in diverse plant metabolic processes. To investigate the potential roles of STPs in cassava (Manihot esculenta) tuber root growth, genome-wide identification and expression and functional analyses of the STP gene family were performed in this study. A total of 20 MeSTP genes (MeSTP1–20) containing the Sugar_tr conserved motifs were identified from the cassava genome, which could be further classified into four distinct groups in the phylogenetic tree. The expression profiles of the MeSTP genes explored using RNA-seq data showed that most of the MeSTP genes exhibited tissue-specific expression, and 15 out of 20 MeSTP genes were mainly expressed in the early storage root of cassava. qRT-PCR analysis further confirmed that most of the MeSTPs displayed higher expression in roots after 30 and 40 days of growth, suggesting that these genes may be involved in the early growth of tuber roots. Although all the MeSTP proteins exhibited plasma membrane localization, variations in monosaccharide transport activity were found through a complementation analysis in a yeast (Saccharomyces cerevisiae) mutant, defective in monosaccharide uptake. Among them, MeSTP2, MeSTP15, and MeSTP19 were able to efficiently complement the uptake of five monosaccharides in the yeast mutant, while MeSTP3 and MeSTP16 only grew on medium containing galactose, suggesting that these two MeSTP proteins are transporters specific for galactose. This study provides significant insights into the potential functions of MeSTPs in early tuber root growth, which possibly involves the regulation of monosaccharide distribution.

Seed Potato Performance after Storage in Light at Elevated Temperatures

In regions with short growth seasons, it is of great importance to use potato (Solanum tuberosum L.) seed tubers with a high growth vigour and a short growth cycle. Such qualities may be obtained by treatments advancing the physiological age of the seed tubers. In this study, we have exposed tubers from four cultivars to various combinations of temperature and light conditions (green-sprouting) for 3–7 months in controlled climate. Subsequent sprout quality, seed tuber health and performance were studied in laboratory, greenhouse and field trials. Satisfactory short, sturdy and leafy sprouts were produced even after 7 months storage at 15 °C under light exposure. An assay of black scurf (Rhizoctonia solani) on the tuber skin showed that light exposure significantly reduced the occurrence compared with dark-stored tubers, while the average effect of storage temperatures was insignificant. In general, green-sprouting advanced emergence and plant growth by 1–2 weeks, and showed early tuber initiation and growth, compared to untreated material. Yields, 107 days after planting in the field trial, did not deviate significantly from untreated tubers. However, plant development at harvest was in accordance with general responses to physiological ageing of potato seed tubers, i.e. still tall and immature plants from untreated tubers, and short and mature plants from aged tubers. Results demonstrated the possibility of successful long-term storage of potato seed tubers in light at elevated temperatures and a potential for earlier harvests and higher early yields from such treatments.

Early drought effect on canopy development and tuber growth of potato cultivars with different maturities

The morphological growth characteristics of shoots, stolons, and tubers were measured on potatoes (Solanum tuberosum L.) grown in irrigation and drought from plant emergence. Three cultivars with a wide range of seasonal maturing patterns, Chubaek (very early), Superior (medium-early), and Jayoung (late), were used. The drought was maintained up to the tuberization stage in the year 2015, and it was extended to early tuber bulking in the year 2016. The drought delayed the time to full canopy development by 2–6days and decreased the growths of shoots in terms of stem length, stem thickness, number of stems, and fresh weight of the shoots. The harvest index was increased in all cultivars due to the decreased shoot growth. The early drought also increased the length of underground stolons. However, the decreases in stem thickness and stem number and the increases in harvest index and stolon length were only significant in the year 2016. Even though the drought did not affect tuberization in early and medium-early cultivars, it decreased early tuber growth by suppressing the longitudinal growth expressed by the ratio of length to width of the tubers. The decrease of tuber growth was observed until the end of the season with the exception of Superior in 2016. In late maturing cultivar, tuber initiation and tuber yield were dependent on the season or length (severity) of the drought. In 2016 when late cultivar, Jayoung, experienced a long drought starting from the emergence of the plants to early tuber bulking, the drought induced earlier tuberization than irrigation treatment, and showed a higher harvest index than in 2015. The early tuberization and tuber bulking due to the long drought induced increased tuber yields. The occurrence of second growth tubers was highly attributed to the maturity of cultivars in both years and the drought in 2016.