Minituber Production Research Articles

EFFECTIVENESS OF BIOCHAR AS SOIL AMELIORANT TO INCREASE SMALL SHALLOT BULBS YIELD FROM TRUE SHALLOT SEED (TSS) IN DRYLAND AGROECOSYSTEM

The decline in soil fertility, characterized by extremely low organic matter content, is a common occurrence in agricultural land due to the intensified practices of crop production. These practices often involve the unwise application of chemical fertilizers and a lack of recycling agricultural waste as organic fertilizers. This study aimed to investigate the impact of biochar on the yield of small shallot bulbs grown from true shallot seed (TSS) in a dryland agroecosystem. The experimental trial was conducted using a randomized block design, incorporating two factors: organic amendments (biochar, manure, and biomass) and TSS varieties (Tuk-tuk, Sanren, and Trisula). The results demonstrated that the use of biochar, particularly in the Trisula variety, resulted in the highest production of mini-tubers, with an average of 4.5 tubers per seed. In comparison, the Sanren variety yielded 1.8 bulbs per seed, while the Tuk-Tuk variety yielded 1.2 bulbs per seed. Furthermore, the application of biochar had a positive influence on soil properties, such as increased levels of organic carbon (C- organic), availability of phosphorus (P-available), and cation exchange capacity (CEC) in dry soils. The utilization of biochar as an organic amendment demonstrated its potential to enhance shallot bulb yield, particularly in the Trisula variety, within a dryland agroecosystem.

Substrate combinations in potato planting to increase the production of minitubers

The profitability and initial development of potatoes depend on the type of substrate used in planting. Therefore, this study aimed to evaluate combinations of substrates for the production of minitubers of potatoes. An experiment was carried out with the combinations of substrates based on sphagnum peat, coconut fiber, rice husks, and expanded vermiculite [TFCV]; and sphagnum peat and expanded vermiculite [TV], in different proportions (100%; 75%; 50%; 25%), with five replications. The treatments were: (i) TFCV100%; (ii) TFCV75%+TV25%; (iii) TFCV50%+TV50%; (iv) TFCV25%+TV75%; and (v) TV100%. At 40 and 70 days after planting (DAP), the development of shoots, tubers, and roots was monitored. Results showed that the isolated application of TV showed the highest production of fresh mass of tubers (93.0 g), and fresh (0.28 g) and dry mass of roots (0.17 g). At 40 DAP, tuber production was highly correlated with the root part (r: 0.77). However, after 70 DAP, tuber production was associated with shoot development (r: 0.66). If is necessary to mix substrates recommend the mixing of TFCV50% + TV50%. The addition of coconut fiber and rice husk increases the availability of nutrients in the substrate with a positive effect on the aerial development of the plants.

The Effects of Different GA3 and Mycorrhiza Dosages on Mini Tuber Production in Potatoes

This study was conducted in 2017 under greenhouse conditions using selected four different potato clones to determine the effects of different doses of GA3 and arbuscular mycorrhizal fungus on mini tuber production. The research, carried out in a randomized complete block design with three replications, applied GA3 doses of 0, 5, 10, and 15 ppm, and mycorrhizal inoculat doses of 0, 500, 1250, and 2000 mg/100 tubers. Parameters including emergence time, plant height, main stem number, tuber number, average tuber weight, tuber size distribution (>45 mm, 28-45 mm, <28 mm), and maturity period were examined. The effect of GA3 application on all investigated parameters except the number of main stems was significant, statistically. The highest mini tuber number (9.1 tubers) and mini tuber yield (408.4 g/pot) were obtained from the application of 15 ppm GA3, while the highest average mini tuber weight (46.74 g) was obtained from the control group. In mycorrhizal applications, the highest tuber number was obtained at a dose of 500 mg/100 tubers, and the highest mini tuber weight and yield were obtained at a dose of 1250 mg/100 tubers. As a result of the study, it was determined that the application of 15 ppm GA3 is suitable due to its positive effect on mini tuber multiplication, and the mycorrhizal application at a dose of 500 mg/100 tubers is appropriate due to its positive effect on increase of tuber number.

Production Of Mini Tuber Potato (Solanum tuberosum L.) Ppt4 Zebra With Aeroponic System Through The Addition Of Lighting Color Settings And Lighting Length

Potatoes (Solanum tuberosum L.) are carbohydrate-rich crops. Low potato productivity in Indonesia stems from farmers' inadequate access to quality seed potatoes. One solution to this issue is enhancing quality seed potato production, achievable through aeroponic systems. Lighting, whether incandescent or LED, can optimize potato mini tuber propagation in aeroponic systems. Research on lighting's effects on potato growth remains incomplete. This study aims to investigate how lighting color and duration affect mini tuber production of Solanum tuberosum L. PPT4 Zebra using aeroponic systems. Conducted in Jurangkuali, Bumiaji sub-district, Batu, the study employed a split plot design. The main plot consisted of lighting colors (WC): light yellow (WK), white (WP), and purple (WU). Subplots were lighting duration (LP) at 3 hours (LP 3) and 5 hours (LP 5), each replicated four times. Each replication comprised 8 samples, with 18 potato plant cuttings per population. Variables included plant height, stem diameter, leaf count, chlorophyll level, root length, tuber count, tuber diameter, budding seed count, and tuber weight. Data were analyzed using F-tests followed by BNJ tests at a 5% significance level. Results indicated no interaction between lighting color and duration. Purple lighting yielded the highest tuber count and weight, while 3-hour lighting duration yielded superior plant height, stem diameter, leaf count, and root length.

Effect of Light Quality on Seed Potato (Solanum tuberose L.) Tuberization When Aeroponically Grown in a Controlled Greenhouse.

A plant factory equipped with artificial lights is a comparatively new concept when growing seed potatoes (Solanum tuberosum L.) for minituber production. The shortage of disease-free potato seed tubers is a key challenge to producing quality potatoes. Quality seed tuber production all year round in a controlled environment under an artificial light condition was the main purpose of this study. The present study was conducted in a plant factory to investigate the effects of distinct spectrum compositions of LEDs on potato tuberization when grown in an aeroponic system. The study was equipped with eight LED light combinations: L1 = red: blue: green (70 + 25 + 5), L2 = red: blue: green (70 + 20 + 10), L3 = red: blue: green (70 + 15 + 15), L4 = red: blue: green (70 + 10 + 20), L5 = red: blue: far-red (70 + 25 + 5), L6 = red: blue: far-red (70 + 20 + 10), L7 = red: blue: far-red (70 + 15 + 15), L8 = red: blue: far-red (70 + 10 + 20), and L9 = natural light with 300 µmol m-2 s-1 of irradiance, 16/8 h day/night, 65% relative humidity, while natural light was used as the control treatment. According to the findings, treatment L4 recorded a higher tuber number (31/plant), tuber size (>3 g); (9.26 ± 3.01), and GA3 content, along with better plant growth characteristics. Moreover, treatment L4 recorded a significantly increased trend in the stem diameter (11.08 ± 0.25), leaf number (25.32 ± 1.2), leaf width (19 ± 0.81), root length (49 ± 2.1), and stolon length (49.62 ± 2.05) compared to the control (L9). However, the L9 treatment showed the best performance in plant fresh weight (67.16 ± 4.06 g) and plant dry weight (4.46 ± 0.08 g). In addition, photosynthetic pigments (Chl a) (0.096 ± 0.00 mg g-1, 0.093 ± 0.00 mg g-1) were found to be the highest in the L1 and L2 treatments, respectively. However, Chl b and TCL recorded the best results in treatment L4. Finally, with consideration of the plant growth and tuber yield performance, treatment L4 was found to have the best spectral composition to grow quality seed potato tubers.

Effect of various concentrations of agar and sucrose on growth and tuberization of four Potato (Solanum tuberosum L.) varieties under in vitro, invivo conditions

The study tends to evaluate the effect of different concentrations of agar treatment (5, 7, and 9 g.l-1) with sucrose (20, 30, and 40 g.l-1) on in vitro shoot regeneration and rooting in one step using tuber-eyes and node explants of four potatoes (Solanum tuberosum L) varieties “Sagitta, Challenger, SM 13–132– 05 and Taurus”, and minitubers production under greenhouses conditions which are going to be grown in Kurdistan -Iraq. The results showed that SM 13–132– 05 cultivar was superior upon the other cultivars under in vitro conditions through multiplication tests (Agar concentration 7 g.l-1 and sucrose concentration 30 g.l-1) and greenhouse conditions by producing the highest shoot multiplication (3.17 shoots/ explant, 12.84 leaves/ explant and 14.51cm mean length of roots) and the best number of minitubers (5.72 minitubers/ plantlet) in greenhouse. Whereas, Challenger had the lowest number of minitubers (3.75/ plantlet). On the other hand, there was no significant differences in the effect of the different concentrations of Agar and sucrose on the four cultivars in terms of the rooting percentage.

In vitro sprouts culture, shoots multiplication and plants acclimatization for commercial production of potato minitubers

In vitro sprouts culture, shoots multiplication and plants acclimatization for commercial production of potato minitubers

Перспективы применения фитотронов для выращивания меристемных растений

One of the progressive and increasingly popular technologies for obtaining virus-free seed material is the accelerated seed production system, which involves the production of minitubers in a controlled environment - phytotrons. An analysis of the existing prospects for the use of phytotron installations for growing meristem plants has been carried out, and their advantages and disadvantages have been identified. Tasks have been set for the use of structures based on an energy-efficient microclimate parameter that affect plant growth in phytotron installations. An analysis of the existing phytotron installations used for growing plants has been carried out. Keywords: PHYTOTRON, CLIMATE, LIGHTING SOURCES, MICROPROPREPARATION, SPECTRUM, PHYTOLEDS, IRRIGATION, NUTRIENT SOLUTION, AIR EXCHANGE

Comparison of minituber production in designed aeroponic system and soil cultivation

Comparison of minituber production in designed aeroponic system and soil cultivation

Mycorrhization of Xanthosoma sagittifolium L. Schott Plants (White Cultivar): Evaluation of Their Effect on Acid Phosphatase Activity During Growth and Production of Minitubers

This work's main objective was to evaluate the effect of certain strains of arbuscular mycorrhizal fungi on acid phosphatase activity during growth. The treatments applied were, control, Glomus intraradices, Acaulospora tuberculata, Gigaspora margarita, Glomus sp., and the mixture of these four AMF strains. Their effect on the growth of vitroplants was evaluated on days 60, 120, and 180 after inoculation. Mycorrhizal status following treatments and acid phosphatase activity were assessed. The minitubers obtained were subjected to a preservation and germination test. The results showed that the maximum growth peak of X. sagittifolium plants was obtained on day 120 for all treatments. The mixture of the four strains of AMF had more influence on the growth parameters with values of 18.40±0.54 Cm and 42.34±16.67 Cm2, respectively for the average number of roots and leaf area. Mycorrhization did not significantly influence the mean number of leaves and mean plant height. Mycorrhizal structures were observed in all mycorrhizal treatments applied. The frequency of mycorrhization was very high in plants inoculated with Glomus sp. The evaluation of the phosphatase activity shows a significant activity at the level of the leaves with a peak of activity in the plants inoculated with Glomus sp. (47.72±0.07 µM/min/g of FW). Compared to the control, the number of minitubers produced was two to three times higher. The best tuberization percentage (80%) was obtained in plants inoculated with a mixture of AMF strains. The temperature of 7~10°C allowed the preservation of 50% of the germination capacity of the minitubers after two months. Based on the obtained results, it was concluded that fertilization with AMF is beneficial for the stimulation of minitubers production.

Produção de minitubérculos de inhame para propagação vegetativa alternativa: tipo de estacas, substratos e anatomia

ABSTRACT: Yam is a tuber vegetable crop with vegetative propagation. The crop is low yielding due to the difficulty of obtaining quality material for propagation and the high cost of acquisition. The cutting technique is a new alternative for vegetative propagation of yam. The present studyevaluated the production of minitubers of yam through cuttings, and follow the formational growth of the minitubers. Different types of cuttings, obtained from three positions on the shoots, and three substrates were tested. The types of cuttings and substrates did not significantly affect the number of minitubers per cutting, this number ranging from 1.18 to 1.75. The best results were obtained using Tropstrato Florestal® and median-position cuttings for the following variables: minituber length (17.47 mm), minituber diameter (12.63 mm), minituber fresh weight (2.12 g), and percentage of cuttings with two minitubers (75%). Anatomical analysis showed cell divisions and starch accumulation in the nodal region at seven days after planting the cutting. Emergence of the minituber could be observed at 21 days. The production of yam minitubers through stem cuttings is enhanced using cuttings obtained from the median position of the shoot and using the commercial substrate Tropstrato Florestal®.

The use of phytohormones to increase the efficiency of potato propagation in nodal cuts culture

Micropropagation of potato in vitro by periodic cutting of plants and passaging them to new nutrient media is the most common approach to obtaining large volumes of planting material in mini-tuber production systems. The article summarizes research data on the effect of gibberellic acid, auxins, and cytokinins on the rate of plant growth and internode formation of potato microplants in vitro. According to the results published in the scientific literature, the greatest efficiency in the process of series cutting of plants can be achieved by using media with a predominance of gibberellic acid in combination with auxins. The use of cytokinins is not relevant within this technology framework.

Introduction of Nutrient Solution of Silicon Sulfonated With Elemental Sulfur S8 for the Mini-tuber Production of Potato Cultivars from in vitro Micro-tuber

This study with aims to investigate the effect of nutrient solution sulfonated silicon with elemental sulfur S8 in the mini-tuber production of potato cultivars in the greenhouse of Potato Research Station of Ardabil Province, Iran was done during April till August of 2022. This experiment was carried out based on the factorial experimental design in two factors and three repetitions. The first factor with two levels including: 1. foliar spraying with nutrient solution sulfonated silicon with elemental sulfur S8 and 2. Control (without nutrient solution sulfonated silicon with elemental sulfur S8) and the second factor consists of micro-tubers of five cultivars in the name of Agria, Jelli, Anosha, T297 and Sheida. The foliar spraying with S-8 nutrient solution was done in five stages of vegetative growth, plant growth and development, tuberization, flowering and tuber development and tuber bulking. The results of analysis of variance showed that there was a significant difference between the levels of nutrient solution, cultivars and the interaction between nutrient solution and cultivars in terms of mini-tuber number and weight per square meter, mini-tuber number per plant and plant height. Anosha cultivar had the highest values in terms of mini-tuber number and weight per square meter and tuber number per plant traits by using nutrient solution and was placed in the group A. The Agria, Jelli, Sheida and T297 cultivars were placed in the group B and had the highest amount by using nutrient solution in terms of these characteristics. The Agria, Jelli and Anosh cultivars had the highest plant height by using nutrient solution. Based on the results, using sulfonated silicon nutrient solution with elemental sulfur S8 causing an increase mini-tuber number per square meter (515 numbers), mini-tuber number per plant (5 numbers), mini-tuber weight per square meter (47 kg) and plant height (92 cm) became.

Effect of Explant Age and Applied IBA on Growth and Rooting of Apical Stem Cuttings of Potato for Early Generation Seed Potato Production

The aim of this work is to study the effect of explant age and exogenously applied IBA on the growth and rooting potential of potato apical stem cuttings for production of first- generation seed potatoes. The experimental protocol consists in taking apical stem cuttings from potato plantlets at different physiological ages (30 and 60 days old) in interaction with the growth regulator indole-3-butyric acid (IBA) at different concentrations (100, 200, and 300 ppm) to study the production of potato minitubers. The results of the present study showed that mini-cuttings from young potato plants (30 days old) have a higher rooting capacity than mini-cuttings from mature plants. In addition, IBA concentrations, especially at 300 ppm, have a significant effect on most of the characteristics studied, e.g. rooting %, root number, root length, shoot length, and number of leaves. Regarding yield attributes, application of IBA at 300ppm gave the highest average tuber number (6.66) and tuber yield (142.97g) was higher in 30days old explant cuttings. The data presented in this study may encourage potato growers to use potato stem cuttings as a new, cheaper method of growing potatoes instead of expensive imported seed tubers. It is suggested that the use of apical stem cuttings can be a quick and effective method for mass propagation and to increase the yield of minitubers in the seed potato production cycle.

MINITUBERS PRODUCTION OF FOUR POTATO (SOLANUM TUBEROSUM L.) CULTIVARS BY TISSUE CULTURE TECHNIQUE

This study was aimed to produce potato minitubers via tissue culture technique by testing four cultivars; Agria, Nicola, SM 12-124-15 and JIP 1600-1 under in vitro, greenhouse and open-air field conditions. Nicola cultivar was superior upon the other cultivars under in vitro and greenhouse conditions by producing the best shoot multiplication (1.89 shoots/ explant and 13..27 leaves/ explant) and the highest number of minitubers (8.87 minitubers/ plant) in greenhouse whereas, SM 12-124-15 was better in the open field conditions by producing 11.25 tubers per plant, recording the highest mean weight of tubers (321.33 g), the highest weight of tubers per plant (3.615 kg), the bigger sizes of tubers (length 8.22 cm: width 3.43 cm) and the highest total yield per hectare (49.70 Ton/ ha). An interesting microtubers formation was noticed on SM 12-124-15 explants grown on MS medium supplemented with 0.5 mg/l-1 BA. The main conclusion drown from the current study is MS medium with basic vitamins and solidified by agar without the need of adding exogenous plant growth regulators can be used for mass seed tubers production based on potato genotype in vitro under optimized culture conditions with a low cost propagation system and shorter period of time than normal minitubers production process.

Potato Aeroponics: Effects of Cultivar and Plant Origin on Minituber Production

Aeroponics is a modern and soilless technology that is used for the efficient production of pre-basic seed potatoes, namely minitubers. This study aimed to evaluate the effects of the cultivar and type of planting material on the production of minitubers in the aeroponic facility in Guča, Serbia, at short, 7-day harvest intervals. Although aeroponic cultivation prolonged the vegetative cycle in all five investigated cultivars, the dynamics of minituber formation varied between genotypes. Two early maturing cultivars, Cleopatra and Sinora, quickly completed the vegetative cycle and formed a small number of minitubers, while the medium-late to late cultivars, Kennebec and Agria, steadily tuberized during the entire cultivation period in the aeroponic facility. The type of planting material affected the dynamics of minituber formation in three investigated cultivars. Sinora, Cleopatra, and Désirée’s plants of in vitro origin reached the final number of minitubers and the vines started senescing much earlier than plants of minituber origin. Kennebec and Agria plants of in vitro origin produced the largest number of minitubers (53.8–54.5) and showed the highest yield (9.8–10.5 kg m−2) during the cultivation period, while the heaviest minitubers were formed by Sinora plants of minituber origin (15.48 g). In addition, the temperature during pre-harvest periods significantly affected the number of tubers at harvests in Kennebec and Agria, and minituber mass in Désirée.

Shoot and root zone temperatures are critical in bidirectional regulation of tuberization in potato

Multiple signals regulate tuberization in potato and among them, photoperiod and temperature are most crucial. Optimum temperature for tuberization is around 20 °C and elevated temperatures above optimum drastically reduces tuberization. Our study therefore aims at understanding and establishing a system to study the effect of shoot and root zone temperatures on tuberization. Towards this, a less photosensitive cultivar, Kufri Jyoti was identified initially by analysing the allelic variations in CDF1 gene. Using the aeroponic systems housed inside the poly house, the effect of temperature on tuberization was studied. Following staggered sowing on aeroponic chambers during rabi season (Oct-Dec), the shoot zone (Sz) and root zone (Rz) were exposed to elevated mean cumulative day temperatures with one set of chambers regulated to maintain optimum temperature of 19 ± 2 °C in Rz (Rz-R) irrespective of date of sowing/ planting. With delayed planting, plants were exposed to high temperatures and our study demonstrated that, elevated temperatures in Sz and/or Rz had significant effect on growth attributes, tuber number and tuber weight per plant. While the tuber number was significantly higher under optimum root and shoot zone temperature, it was rather decreased by 3.5 and 2.3 for every degree rise in Rz (irrespective of Sz) and Sz (irrespective of Rz) temperature, respectively. However, regulating the Rz temperature inside the aeroponic chambers, reasonably a good number of mini-tubers per plant was produced regardless of the shoot zone temperatures suggesting that, root temperature is more crucial than shoot temperature. Furthermore, reduction in tuberization at elevated temperature was correlated well with reduction in expression of key positive regulators (StSP6A, StBEL5) and enhanced expression of key negative regulator, StSP5G in both leaves and solons. Taken together, our data suggest that, regulation of both root and shoot zone temperatures are important for effective tuberization and tuber yield in potato. • Elevated shoot zone (Sz) and root zone (Rz) temperature above optimum significantly affected plants growth and tuber yield. • Every degree rise in Sz and Rz zone temperature above optimum resulted in significant reduction in tuber number and weight. • Root zone temperature is more critical in regulating tuber number and tuber weight than shoot zone temperature. • At elevated Sz and Rz temperatures, expression of positive and negative regulators decreased and increased respectively. • Regulating Rz temperature would likely to help maintain mini-tuber production even under non-optimal shoot zone conditions.

Comparison of aeroponics and conventional system of production of potato mini-tubers in the conditions of the Czech Republic

Aeroponics would appear to have a number of potential attributes to make potato production more efficient. In a 3-year experiment, from 2019 to 2021, potatoes were grown in aeroponic units using two nutrient solutions as well as in a conventional polycarbonate greenhouse in a substrate. Potato cultivars Adéla, Zuza and Ornella were used in all experiment years. No statistically significant effect of nutrient solution or potato cultivar on the number and weight of tubers was found in the trial. However, the advantages of aeroponics over conventional technology were statistically proven. The number of tubers per plant in aeroponic units ranged from 2.4 (2019, cv. Adéla) to 41.0 (2021, cv. Zuza), while in the greenhouse, they ranged from 3.9 (2019, cv. Adéla) up to 12.6 (2021, cv. Adéla). The average weight of tubers in aeroponic units ranged between 2.0 g and 9.9 g per plant (2 to 10 successive harvests), and in the greenhouse, 22.7 g to 41.9 g per plant (single harvest). The influence of cultivar on the average weight of tubers within individual cultivation technology variants was statistically proven only for polycarbonate greenhouse: only one harvest after the end vegetation.

High Microplant Densities in Greenhouses – Are they Always Efficient in Small Potato Minituber Production Systems?

High Microplant Densities in Greenhouses – Are they Always Efficient in Small Potato Minituber Production Systems?

Production of potato (Solanum tuberosum) pre-basic seed through tissue culture in Katibougou, Mali

Abstract. Abdoulaye M, Blay ET, Eleblu JSY. 2021. Production of potato (Solanum tuberosum) pre-basic seed through tissue culture in Katibougou, Mali. Cell Biol Dev 5: 90-104. In Mali, the main problem limiting the productivity and production of potatoes is the non-availability of quality seeds in adequate quantities and at affordable prices. This study proposes two experiments on the techniques adopted in Mali's IPR/IFRA plant biotechnology laboratory to meet quantity and quality improvements. That evaluation of the effects of 3 concentrations of coconut water and 2 of potassium nitrate on potato plantlets growth in vitro and of 2 physiological ages and 3 substrates on potato in vitro plants' establishment, post in vitro growth, and mini tubers production in vivo. The first experiment was a Completely Randomized Design (CRD) with 12 treatments replicated 4 times. The second was a factorial experiment with 2 factors (physiological ages: 2 levels and substrate: 3 levels) in a Randomized Complete Block Design (RCBD) with 6 treatments replicated 4 times. The first experiment showed that the culture medium M7 (MS+40 mL/L of coconut water +250 mg of potassium nitrate) had promoted all plant growth parameters (shoot emergence, plant height, number of nodes, leaves and roots, and plant fresh and dry weight) after 30 days of in vitro culturing. The lower concentrations of coconut water (40 mL) and potassium nitrate (250 mg) per liter of MS medium had significant and positive effects on all the in vitro growth parameters after 30 days. The second experiment showed that the plantlet weaning age of 25 days and the post-flask culture substrate S1 (only soil) provided the best plant survival percentage at 20 days after transplanting in vivo. The substrate S2 (soil and cow dung 2:1) positively affects plant stem length, stem diameter, fresh and dry biomass formation, tuber yield, tuber numbers per plant, and tuber grading size B (tubers with a diameter of less than 28 mm). The substrate composition S1 (only soil) has significantly affected the weight loss (12.50%) of tubers stored within 8 weeks. The weaning age was 45 days, and the substrates S2 (soil and cow dung 2:1) and S3 (soil and cow dung 1:1) significantly reduced the number of sprouts per tuber and sprouts number per eye on tubers. In addition, the results indicate that for the better and more rapid growth of potato plantlets in vitro culture, the coconut water concentration used as a supplement to MS medium should be 40 mL per liter of medium. The proportion of cow dung used in substrate composition should not exceed the soil and cow dung ratio 2:1 for maximum post-transplanting plant re-establishment rate in vivo and rapid maturity of mini-tubers.