Early Tuber Research Articles

Tuber Water and Pressure Potentials Decrease and Sucrose Contents Increase in Response to Moderate Drought and Heat Stress

Environmental stress during the growing season can reduce the quality of stored Solanum tuberosum (potato) tubers. Changes in greenhouse grown Russet Burbank tuber water potential and tuber composition following periods of moderate drought, heat, or drought and heat stress were characterized. Decreased leaf and tuber water potentials were observed at the end of stress treatments. Decreased tuber water potential caused dramatic declines in tuber pressure potential. Tuber sucrose content increased with the severity of stress. Changes in tuber glucose and malic acid contents were also observed. Stress during early tuber bulking had a larger effect on tuber sugars at the end of the stress period than stress during late bulking. Stem-end glucose concentration of tubers at harvest after vine senescence was greater in tubers from plants stressed at early tuber bulking compared to late bulking.

Physiology of the Potato: New Insights into Root System and Repercussions for Crop Management

Potato roots are concentrated mostly in the plow layer up to 30 cm in soil depth. Some roots extend up to 100 cm depth and the total root length throughout the soil profile reaches about 10–20 km m−2 area. There are large differences in root mass (dry weight and length) in the plow layer between cultivars, breeding lines and wild relatives. The differences are generally stable across different environmental conditions, such as locations with different soil types, fertilizer rates and planting densities. Under favourable environmental conditions without severe shortage of water and nutrients, root mass differences between genotypes are related to maturity class: late genotypes continue root growth longer, and attain larger root mass and deeper rooting than early genotypes. Differences in root mass become clear at the start of flowering, much earlier than differences in shoot mass. Root mass is negatively correlated with early tuber bulking. However, root mass generally shows positive correlations with shoot mass and final tuber yield. Differences in root mass also exist amongst genotypes of the same maturity class. Using root mass in the plow layer and tuber yield as selection criteria, Konyu cultivars were bred in Japan. They showed significantly less reduction of leaf conductance and photosynthesis, leaf area and tuber yield than commercial cultivars under dry soil conditions. To assist breeding for root characters, new methods have been developed to assess the ability of roots to penetrate into hard soil layers using pots with paraffin-vaseline discs and the ability to absorb under low water potential in vitro. Physiological research on root characteristics contributed in the past, and will continue to do so in the future, to the development of new cultivars with high drought tolerance and to the improvement of irrigation practice.

IbMADS1 (Ipomoea batatas MADS-box 1 gene) is involved in tuberous root initiation in sweet potato (Ipomoea batatas).

Background and AimsThe tuberization mechanism of sweet potato (Ipomoea batatas) has long been studied using various approaches. Morphological data have revealed that the tuberizing events result from the activation of the cambium, followed by cell proliferation. However, uncertainties still remain regarding the regulators participating in this signal-transduction pathway. An attempt was made to characterize the role of one MADS-box transcription factor, which was preferentially expressed in sweet potato roots at the early tuberization stage.MethodsA differential expression level of IbMADS1 (Ipomoea batatas MADS-box 1) was detected temporally and spatially in sweet potato tissues. IbMADS1 responses to tuberization-related hormones were assessed. In order to identify the evolutionary significance, the expression pattern of IbMADS1 was surveyed in two tuber-deficient Ipomoea relatives, I. leucantha and I. trifida, and compared with sweet potato. In functional analyses, potato (Solanum tuberosum) was employed as a heterologous model. The resulting tuber morphogenesis was examined anatomically in order to address the physiological function of IbMADS1, which should act similarly in sweet potato.Key ResultsIbMADS1 was preferentially expressed as tuberous root development proceeded. Its expression was inducible by tuberization-related hormones, such as jasmonic acid and cytokinins. In situ hybridization data showed that IbMADS1 transcripts were specifically distributed around immature meristematic cells within the stele and lateral root primordia. Inter-species examination indicated that IbMADS1 expression was relatively active in sweet potato roots, but undetectable in tuber-deficient Ipomoea species. IbMADS1-transformed potatoes exhibited tuber morphogenesis in the fibrous roots. The partial swellings along fibrous roots were mainly due to anomalous proliferation and differentiation in the xylem.ConclusionsBased on this study, it is proposed that IbMADS1 is an important integrator at the initiation of tuberization. As a result, the initiation and development of tuberous roots seems to be well regulated by a network involving a MADS-box gene in which such hormones as jasmonic acid and cytokinins may act as trigger factors.

StGA2ox1 is induced prior to stolon swelling and controls GA levels during potato tuber development

The formation and growth of a potato (Solanum tuberosum) tuber is a complex process regulated by different environmental signals and plant hormones. In particular, the action of gibberellins (GAs) has been implicated in different aspects of potato tuber formation. Here we report on the isolation and functional analysis of a potato GA 2-oxidase gene (StGA2ox1) and its role in tuber formation. StGA2ox1 is upregulated during the early stages of potato tuber development prior to visible swelling and is predominantly expressed in the subapical region of the stolon and growing tuber. 35S-over-expression transformants exhibit a dwarf phenotype, reduced stolon growth and earlier in vitro tuberization. Transgenic plants with reduced expression levels of StGA2ox1 showed normal plant growth, an altered stolon swelling phenotype and delayed in vitro tuberization. Tubers of the StGA2ox1 suppression clones contain increased levels of GA20, indicating altered GA metabolism. We propose a role for StGA2ox1 in early tuber initiation by modifying GA levels in the subapical stolon region at the onset of tuberization, thereby facilitating normal tuber development and growth.

Is there a trade‐off between aggressiveness and overwinter survival in Phytophthora infestans?

Summary Selection during interepidemic stages is crucial for the evolution of pathogen populations. Trade‐offs involving aggressiveness (quantitative pathogenicity) have rarely been explored in pathogens with a life cycle requiring the disease‐causing organism to change organs within the same host. We investigated the existence of a trade‐off between aggressiveness and survival in Phytophthora infestans, the pathogen causing potato late blight. In France, P. infestans behaves as an obligate biotroph, surviving in infected tubers. Aggressive isolates, which are favoured during the epidemic, may exhaust their nutrient supply too quickly to bridge seasons, resulting in a possible trade‐off between the two life stages. We inoculated tubers with isolates possessing different aggressiveness levels, let them overwinter as outdoor piles at three different sites, and scored the proportion of live tubers the following spring. At two sites, infection caused early tuber sprouting, which can be seen either as a manipulation of the host by the pathogen, or as an attempt by the host to escape. Overwinter survival was higher for control than for inoculated tubers, but did not differ between tubers inoculated with different isolates. This suggests that aggressiveness should gradually increase in P. infestans populations, unless a trade‐off occurs at another stage of the life cycle.

Overexpression of a bacterial 1-deoxy-D-xylulose 5-phosphate synthase gene in potato tubers perturbs the isoprenoid metabolic network: implications for the control of the tuber life cycle

Potato tubers were engineered to express a bacterial gene encoding 1-deoxy-D-xylulose 5-phosphate synthase (DXS) in order to investigate the effects of perturbation of isoprenoid biosynthesis. Twenty-four independent transgenic lines out of 38 generated produced tubers with significantly elongated shape that also exhibited an early tuber sprouting phenotype. Expression analysis of nine transgenic lines (four exhibiting the phenotype and five showing a wild-type phenotype) demonstrated that the phenotype was strongly associated with dxs expression. At harvest, apical bud growth had already commenced in dxs-expressing tubers whereas in control lines no bud growth was evident until dormancy was released after 56-70 d of storage. The initial phase of bud growth in dxs tubers was followed by a lag period of approximately 56 d, before further elongation of the developing sprouts could be detected. Thus dxs expression results in the separation of distinct phases in the dormancy and sprouting processes. In order to account for the sprouting phenotype, the levels of plastid-derived isoprenoid growth regulators were measured in transgenic and control tubers. The major difference measured was an increase in the level of trans-zeatin riboside in tubers at harvest expressing dxs. Additionally, compared with controls, in some dxs-expressing lines, tuber carotenoid content increased approximately 2-fold, with most of the increase accounted for by a 6-7-fold increase in phytoene.

Process and Product: Recirculating Hydroponics and Bioactive Compounds in a Controlled Environment

NASA has investigated the use of recirculating nutrient film technique (NFT) systems to grow higher plants on long-duration space missions for many years and has demonstrated the feasibility of using recirculating systems on numerous crop species. A long duration (418-day) experiment was conducted at Kennedy Space Center, Fla., to evaluate the feasibility of using recirculating hydroponics for the continuous production of Solanum tuberosum L. `Norland'. The productivity of four sequential batch plantings was compared to staggered harvest and plantings. The accumulation of bioactive organic compounds in the nutrient solution resulted in reduced plant height, induced early tuber formation, and increased harvest index of the crops in both production systems. The changes in crop development were managed by increasing planting density and reducing cycle time to sustain production efficiency.

Effect of nonwoven polypropylene covers on early tuber yield of potato crops

In this six-year research study the effect of nonwoven polypropylene covering on the quantity and quality of early potato yield was estimated. The use of nonwoven polypropylene covers resulted in an increase in the tuber yield and smaller yield variability in the various years, when compared with the traditional cultivation, especially at a very early date of potato harvest. In the cultivation with nonwoven polypropylene covering, the marketable tuber yield 60 days after planting was higher by 23.34% on average and 75 days after planting by 10.92% in the six-year period of the study, compared with the cultivation with no plant covering. The higher profitable effect of covering was obtained in the years with cold spring. The cultivation method of the potato did not affect the chemical composition of the tubers harvested after 60 days from planting. After 75 days from planting the tubers of potato cultivated under nonwoven polypropylene covers contained, on average, more dry matter and starch by 0.81% and 0.85%, respectively.

Restoration of tuber production by exposure to unshaded daylight in Eleocharis kuroguwai Ohwi shaded during the early tuber formation period

The loss of final tuber weight of Eleocharis kuroguwai Ohwi by shading during the early tuber formation period (TFP) is overcome by exposure to unshaded daylight thereafter (late TFP). In the present study, the growth parameters that contribute to the dry matter increase (DMI) per day of tubers in the late TFP were examined. DMI of the tuber during the late TFP was determined by that of the whole plant and the ratio of the DMI of the tuber to that of the whole plant during this period. The ratio of the DMI of the tuber to that of the whole plant during the late TFP was significantly correlated with the DMI of the whole plant during the first 14 days of the late TFP. During the late TFP after the exposure to unshaded daylight, DMI of the whole plant correlated with the surface area of the stem (SAS) and net assimilation ratio (NAR), and the SAS correlated with the stem dry weight (DW) and specific stem‐surface area (SSA). SSA negatively influenced NAR, but NAR was increased by unshading. During the late TFP after shading, the effect of the decrease of the stem DW due to shading on the DMI of the whole plant was mitigated by the large SAS and high NAR. These results indicate that the growth parameters that contribute to the DMI of tuber during the late TFP after exposure to unshaded daylight are SAS and NAR just after unshading, and SSA during this period.

Response of potato tuber cell division and growth to shade and elevated CO2.

Plants adjust their sink-organ growth rates, development and distribution of dry matter in response to whole-plant photosynthate status. To advance understanding of these processes, potato (Solanum tuberosum L.) plants were subjected to CO(2) and light flux treatments, and early tuber growth was assessed. Atmospheric CO(2) (700 or 350 micro mol mol(-1)) and light flux (shade and control illumination) treatments were imposed at two growth stages: tuber initiation (TI) and tuber bulking (TB). Elevated CO(2) increased accumulation of total net biomass when imposed at both stages, and increased tuber growth rate by about 36 %, but did not increase the number of tubers. Elevated CO(2) increased the number of cells in tubers at both TI and TB stages, whereas shade substantially decreased the number of cells at both stages. Generally, treatments did not affect cell volume or the proportion of nuclei endoreduplicating (repeated nuclear DNA replication in the absence of cell division), but the shade treatment led to a decrease in cell volume at TB and a decrease in endoreduplication at TI. Elevated CO(2) increased, and shade decreased, glucose concentration and soluble invertase activity in the cambial zones at both TI and TB, whereas sucrose concentration and activities of glucokinase, fructokinase, cell-wall-bound invertase and thymidine kinase were unaffected. Modulation of tuber cell division was responsible for much of the growth response to whole-plant photosynthate status, and treatments affected cambial-zone glucose and soluble invertase in a pattern suggesting involvement of a glucose signalling pathway.

Effects of elevated CO 2 and/or ozone on nutrient concentrations and nutrient uptake of potatoes

Potato crops were grown at seven sites across Europe to test the effects of elevated atmospheric carbon dioxide and/or tropospheric ozone concentrations on growth, yield and various aspects of potato tuber quality within the framework of the EC funded programme Changing Climate and Potential Impacts on Potato Yield and Quality (CHIP). Field exposure systems were used to enrich the atmosphere in CO 2 and/or ozone. At five of the sites, nutrient element conconcentrations (macronutrients: nitrogen, phosphorus, potassium, calcium, magnesium, and micronutrients: mangenese, zinc, iron) in different parts of plants from the various treatments were analysed. Under elevated CO 2, nearly all nutrient elements tended to decrease in concentration. At maximum leaf area, a significant reduction was observed for the concentrations of nitrogen and potassium both in aboveground biomass and in tubers, and for calcium in tubers. Since CO 2 enrichment promoted early tuber growth, these effects could in part be attributed to tuber developmental stage. At maturity, potato grown under CO 2 enrichment exhibited significantly lower concentrations of nitrogen, manganese and iron in aboveground organs, and of nitrogen, potassium and magnesium in tubers which means a reduction of tuber quality. In contrast to CO 2, elevated ozone tended to increase tuber nutrient element concentrations. This was significant for nitrogen and manganese. CO 2 effects on tuber biomass increase were more pronounced than CO 2 effects on nutrient element decrease. Thus, the total amount of nutrient elements taken up by potato crops increased under elevated CO 2. Fertiliser practice in a future, CO 2-rich world will have to be adjusted accordingly.

Effect of Shoot Removal During Tuberization on Volunteer Potato (Solanum tuberosum) Tuber Production1

Volunteer potato can be a host of serious pest problems in potato and could provide a source of inoculum for subsequent potato crops. Volunteer potato can also be difficult to control in many rotational crops. Potato shoots were removed once, twice, and throughout the growing season, beginning at early and late tuberization. Compared with no shoot removal, two or more shoot removal treatments reduced the number of tubers 42% or more. A single shoot removal treatment at early tuberization reduced tuber biomass 37%, compared with 65% when shoot removal was initiated several weeks later. Regardless of timing, a single shoot removal increased the number and biomass of small tubers (≤ 57 g each). Control tactics that remove or kill volunteer potato shoots require repeated application or integration with other management practices to suppress the weed. Nomenclature: Volunteer potato, Solanum tuberosum L.; potato, Solanum tuberosum L. ‘Russet Burbank’. Additional index words: Groundkeeper, time of removal.

Response to paclobutrazol of symbiotic mycorrhizal fungi and dropper (tuber stalk) formation of host orchid seedlings

The effects of the triazole compound paclobutrazol on the mycorrhizalfungi and production of droppers (tuber stalks) in three species of terrestrialorchids of southwestern Australia were investigated. Seedlings ofDiuris laxiflora Lindley (bee orchid), Microtismedia R. Br. (common mignonette orchid), and Pterostylissanguinea D. Jones & M. Clements (dark banded greenhood orchid)were cultured symbiotically with specific mycorrhizal fungi invitro. The mycorrhizal fungi of the study species were grown on mediacontaining paclobutrazol at 0, 1.7, 3.4, 10.2, or 17.0 μM(corresponding to 0, 0.5, 1.0, 3.0, or 5.0 mgL−1). Paclobutrazol at all concentrations evaluateddecreased the growth rates of the mycorrhizal fungi of M.media and P. sanguinea below that of thecontrol. However, paclobutrazol did not adversely affect the growth of themycorrhizal fungus of D. laxiflora, and low concentrations(1.7 or 3.4 μM) stimulated the growth of this fungus. Symbiotic seedlings of the study species were exposed to paclobutrazolat 0, 1.7, 3.4, 10.2, or 17.0 μM. Paclobutrazol at allconcentrations evaluated increased dropper (tuber stalk) production inD. laxiflora, but had no effect on M.media and P. sanguinea. This suggests that, for species in which paclobutrazol has no fungicidaleffect on mycorrhizal fungi, it has the potential to stimulate early andefficient tuberization of symbiotic orchid seedlings.

Regulation of potato tuberization by daylength and gibberellins

Tuberization of S. tuberosum ssp andigena is induced by short days (SD) and prevented by long days (LD) or by interruption of the long nights with a 30 min night break (SD+NB). Antisense inhibition of the StGA20ox1 gene, encoding the GA 20-oxidase biosynthetic enzyme results in early tuberization in SD, but does not overcome the need of SD conditions for tuber induction. Using RT-PCR differential display of leaves from plants grown under inductive (SD) and non-inductive (SD+NB) conditions we have isolated clone PHOR1 encoding a novel arm-repeat containing protein with homology to Drosophila armadillo. PHOR1 mRNA oscillates with a diurnal rhythm and is up-regulated in plants induced for tuberization. Transgenic lines inhibited in PHOR1 expression are semi-dwarf and show a reduced response to GAs, which is consistent with a function of PHOR1 in GA signaling. These results indicate that changes in GA sensitivity are involved in mediating tuber induction.

Ori, Idit, Zohar and Zahov: Tablestock and chipstock cultivars bred for adaptation to Israel

The cultivars Ori, Idit, Zohar, and Zahov have been bred specifically for adaptation to the Mediteranean climate: Ori and Idit are early tablestock cultivars, Idit is suited for “mini potatoes” (20 to 35 mm in diameter); Zohar is a midseason tablestock cultivai-, and Zahov is used as an early chipstock cultivar. The cultivars can be grown in either of the two main seasons in the Mediterranean region: the spring season (January through July) and the winter season (September through March). The cultivars have rapid emergence and early tuber set, they are tolerant to high temperatures and drought, and are not susceptible to external or internal defects. In field experiments, Idit yields were lower than the cultivar checks (Alpha, Nicola, or Desiree) in six of seven trials. However, the attractive appearance of the small oval tubers (20-35 mm in diameter) and the good aroma of the baked tubers are advantages. Yield of Ori and Zohar occasionally exceeded those of cultivar checks, and their yellowish skin, especially in sandy soils, is an advantage. Yields and tuber dry matter content of the early-maturing cultivar Zahov were similar to Hermes, a standard chipstock cultivar commonly used in Israel. The early maturation of Zahov is desirable to extend the harvest season.

Development of micropropagated potato plants over three phases of growth as affected by temperature in different phases

To assess (after)effects of temperature on plant development, in vitro potato plantlets produced at 17 or 23 °C (normalisation phase, 3 weeks) were planted into soil in growth chambers at 18/12 or 26/20°C (transplant production phase, 2 weeks), and transplanted to glasshouses at 18/12 or 26/20°C (tuber production phase, 6 weeks). The latter phase commonly takes place in the field. Transition from one phase to another, especially from in vitro to in vivo conditions, greatly increased leaf growth and to a smaller extent stem growth. Within a phase, higher temperature stimulated vegetative growth, but delayed tuber formation and reduced tuber yields, harvest index (HI) and tuber dry matter concentration. Temperature during tuber production was more important for high yield than temperatures during earlier phases. Normalisation and transplant production temperatures nevertheless showed after-effects in later phases. Lower normalisation temperatures advanced plant development: they increased vegetative growth in subsequent phases and finally increased fresh tuber yield and HI. This could have yield advantages at locations where field production seasons are short. Lower transplant production temperatures reduced vegetative growth in the next phase, but enhanced early tuber production. Finally they increased tuber dry weight and HI when tuber production temperatures were high. This may increase yield at locations where field conditions delay tuber formation.

Developmental changes in enzymes involved in the conversion of hexose phosphate and its subsequent metabolites during early tuberization of potato

ABSTRACTA highly synchronized in vitro tuberization system, based on single‐node cuttings containing an axillary bud, was used to investigate the activity patterns of enzymes involved in the conversion of hexose phosphates and related products during stolon‐to‐tuber transition of potato (Solanum tuberosum L.). At tuberization the activity of enzymes involved in glycolysis and the oxidative pentose phosphate pathway (OPPP) showed a small but clear increase. This increase reflects a higher capacity of respiratory(‐related) metabolism, presumably due to the onset of rapid cell division in the apical part of the tuberizing stolon. During the phase of successive tuber growth these enzymes decreased in activity, suggesting that the concomitant massive starch accumulation is not accompanied by a large increase in respiration. A high degree of positive correlation between the activities of these enzymes could be observed, implying that the level of respiratory metabolism‐related enzymes is co‐ordinately regulated by the same mechanism of coarse control. The activity pattern of pyrophosphate:fructose‐6‐phosphate phosphotransferase (PFP) showed no developmental change and does not resemble the activity pattern of the enzymes participating in respiratory(‐related) metabolism. Instead, its level of activity is very likely the result of metabolic regulation. The level of the content of the metabolites UDP‐glucose (UDPGlc) and glucose‐6‐phosphate (Glc6P) decreased after the onset of tuberization. This decline indicates that tuber induction is not accompanied by an appreciable increase in the level of the cytosolic hexose phosphate (hexose‐P) content but that it rather remains on a low level, which might be a prerequisite in order to maintain a high net rate of sucrose degradation during tuber development. In contrast to UDPGlc and Glc6P, the content of fructose‐1,6‐bisphosphate (Fru1,6bisP) showed an increase after tuber induction. The overall activities of ADP‐glucose pyrophosphorylase (AGPase) and starch phosphorylase (STP) both showed a large increase after tuber initiation, which is consistent with their presumed role in the process of starch synthesis and accumulation during rapid tuber growth.

Jerusalem artichoke growth, development, and field storage. I. Numerical assessment of plant part development and dry matter acquisition and allocation

Expanding commercial interest in the use of inulin as a bulking agent for artificial sweeteners, dietary fiber health supplement, fat replacement for processed foods, feed stock for fructose syrups, and a wide range of potential industrial products, has stimulated research on inulin‐containing crops such as the Jerusalem artichoke. To better understand the developmental physiology of the crop and to identify potential breeding objectives, the temporal pattern of development of individual plant parts (shoots, branches, leaves, flowers, stolons, tubers, and roots) and the allocation of dry matter into the same plant parts were monitored in the cultivar ‘Sunchoke’ over the entire growing season and during in situ field storage during the early winter, 32 weeks after planting. While number of shoots (∼9) peaked in week 10, the number of branches (42.8), stolons (49.4), and tubers (85.5) reached a maximum 24–28 weeks after planting. Number of leaves (∼525) peaked between weeks 20–24 after planting, as did number of flowers (∼55). The Jerusalem artichoke allocated the major portion of its dry matter (dm) into aboveground plant parts during the first half of the growing season. Approximately 16 weeks after planting, the pattern of allocation shifted dramatically with: a) near cessation in the acquisition of dry matter; and b) the reallocation of existing dry matter from the aboveground organs into the tubers. By the 16th week after planting, 85% of the total dm was in the aboveground plant parts, but declined to 28% by the 30th week. Of the total dm, 92% was accrued during the first 16 weeks and only 8% thereafter. The shift in dry matter resources coincided with a dramatic decrease in leaf number and in leaf and branch dry weight. By the end of the season, the harvest index reached 0.70 and the tuber yield 14.61 dm ha−1. Yield improvement could potentially be facilitated through lengthening the logarithmic period of carbon fixation and by earlier tuber induction and development.

Similarity of QTLs detected for in vitro and greenhouse development of potato plants

A relationship between quantitative trait loci (QTLs) detected for in vitro and greenhouse growing conditions was studied in a backcross population of 155 genotypes derived from a haploid potato (Solanum tuberosum) and a diploid wild species (S. berthaultii). Both plant height and tuberization earliness were characterized under two growing conditions. Main-effect QTLs and QTLs identified only through interaction were detected for each of the traits. For traits associated with plant height as well as for traits associated with early tuberization, the most significant QTL detected for greenhouse cultivated plants was also found when the population was grown in vitro. The most significant QTL for earliness of tuberization in vitro, which was located on chromosome 8, coincides with that detected for sucrose concentration in leaf exudate. The absence of a S. berthaultii allele was associated both with a higher amount of sucrose in the exudate and with earlier in vitro tuber formation. Epistasis was found to have a significant effect on all traits investigated. The QTL model that included main-effect QTLs and all significant interactions explained 83–88% of the total genetic variance for each of the developmental traits. The possibility of using an in vitro system combined with marker-assisted selection for preliminary selection of early tuberizing clones is discussed.

The Presence of Starch Grains on Prehistoric Stone Tools from the Humid Neotropics: Indications of Early Tuber Use and Agriculture in Panama

One of the greatest challenges faced by Neotropical archaeobotanists is to document the origins and history of crops like manioc (Manihot esculentaCrantz), yams (Dioscorea spp.) and sweet potato (Ipomoea batatas), which were grown for their starch-rich underground organs. The records left by early Europeans make it clear that such plants provided a staple food source for numerous indigenous populations in southern Central America and South America (Sauer, 1950). However, the history of these and other tuber crops is very poorly understood because they generally do not leave fossilized remains that can be recovered in archaeological sediments.Starch grain analysis has the potential to help in our understanding of tropical plant domestication. Starch grains, microscopic granules within the plant where the plant's energy is stored, are produced in abundant numbers and varied morphological forms in tuberous and other crop plants, such as maize and beans. Starch grains indistinguishable in morphology and size from modern varieties ofManihot esculenta,Dioscoreaspp.,Zea mays, andMaranta arundinaceahave been isolated from the surfaces of stone tools from archaeological sites in the lowland Central American tropics that date to the last 8000 radiocarbon years. Starch grains also provide important data about the functions of stone grinding tools recovered from early archaeological sites in the humid and lowland Neotropics.