Sweetpotato Cuttings Research Articles

First Report of a Begomovirus Infecting Sweetpotato in Kenya

Previous surveys for viruses in sweetpotatoes (Ipomoea batatas) in Africa did not assay for the presence of begomoviruses such as Sweet potato leaf curl virus (SPLCV), which have been found recently in the Americas and Asia. Symptomatic sweetpotato plants, including some with leaf curling symptoms similar to those observed in SPLCV-infected sweet-potato plants (2), were collected from a germplasm collection plot at Kakamega Research Station in Western Kenya during February 2005. Whiteflies, the vectors for begomoviruses, were observed in the same plots. Ipomoea setosa plants graft-inoculated with scions from the symptomatic sweetpotato developed leaf curl, leaf roll, interveinal chlorosis, and stunting symptoms similar to those caused by infection with SPLCV alone or in combination with Sweet potato feathery mottle virus. Total DNA was isolated from 10 I. setosa plants using the GenElute Plant Genomic DNA Kit (Sigma-Aldrich Inc., St. Louis, MO). Sweetpotato cuttings from 39 clones, selected from the Kenyan germplasm collection for their resistance or susceptibility to sweetpotato virus disease (SPVD), were sent to the Plant Germplasm Quarantine Office of USDA-ARS. The cuttings were planted in a greenhouse. Total DNA was extracted from sweetpotato leaves 1 month later using a cetyltrimethylammoniumbromide (CTAB) extraction method (1). Degenerate primers SPG1/SPG2, developed for PCR detection of begomoviruses (1), amplified a 912-bp DNA fragment from 3 of 10 DNA extracts from I. setosa and 5 of 39 sweetpotato plants held in quarantine. The primers anneal to regions of open reading frame (ORF) AC2 and ORF AC1 that are highly conserved in begomoviruses infecting sweetpotato. SPLCV-specific primers PW285-1/PW285-2 (2) amplified a 512-bp DNA fragment of ORF AC1 from seven samples (two from I. setosa and five from I. batatas). Amplicons from three independent PCR assays of two samples and single PCR assays of four additional samples were cloned into the pGEM-T Easy vector. Clone inserts were sequenced, and compared with sequences deposited in GenBank using the basic local alignment search tool (BLAST). Sequences were closely related to SPLCV (GenBank Accession No. AF104036) with nucleotide sequence identities varying from 93% (GenBank Accession No. DQ361004) to 97% (GenBank Accession No. DQ361005). The presence of the virus poses a challenge to the dissemination of planting materials in the region because begomovirus-infected plants often do not show symptoms. To our knowledge, this is the first report of a begomovirus infecting sweetpotato in Kenya or the East African Region.

Effect of continuous or intermittent radiation on sweet potato plantlets in vitro

SummarySingle-node cuttings of sweet potato [(Ipomoea batatas (L.) Lam. ‘Beniazuma’)] were cultured in vitro for 35 d under intermittent blue light (IB), intermittent red light (IR) and intermittent blue-plus-red light (IBR) provided by light-emitting diodes (LEDs) flashing for 10 s three-times min–1. Growth was compared with cuttings cultured under continuous blue (B), red (R) or blue-plus-red (BR) light, or cool-white fluorescent lamps (FL) with a 16 h photoperiod. Dry weights, leaf areas and carbohydrate contents were greater under the IB and IBR treatments than in the FL treatment. Our results show that a novel light source during in vitro culture of sweet potato plantlets may provide an opportunity to improve plant yield in large-scale greenhouses for commercial purposes.

Phosphorus Content of an Acid Soil and Sweetpotato Uptake as Affected by Nitrogen Application

A pot experiment was conducted to study the changes in P content of acid soil as affeced by different N levels and sweetpotato uptake. Thirty cm healthy cuttings of VSP-2 sweetpotato were planted in clay pots filled with 10 kg soil acid soil. These were applied with 45, 90, 135 and 180 kg N/ha applied at five planting intervals as follows: T1- all at plantingl T2 - all at one month after planting; T3 - 1/2 at planting and 1/2 at one month after planting; T4 - 1/2 at planting and 1/2 at two months after planting at T5 - 1/3 at planting, 1/3 at one month after planting and 1/3 at two months after planting. Application of N fertilziers enchanced the availability of added inorganic P in acid soil and the P uptake of sweetpotato. Reduction in P content of acid soil was observed at different stages of plant growth and this was most evident at harvest. An exponential relationship was established between P removed from acid soil at harvest and root yield, emphasizing the important role played by phosphorus aside from N and K in root growth and formation of sweetpotato.

Pest damage in sweet potato, groundnut and maize in north-eastern Uganda with special reference to damage by millipedes (Diplopoda)

Field experiments were conducted in Soroti District, north-eastern Uganda, an area with two rainy seasons per calendar year, the first one with long, reliable rains and a second one with short, less reliable rain. The trials were with sweet potato ( Ipomoea batatas (L.) Lamk), groundnut ( Arachis hypogaea L.) and maize ( Zea mays L.) and aimed at collecting information on the incidence of millipede damage. Failure of sweet potato cuttings to establish caused by biotic stress varied from 4 to 33%. A significant but variable proportion of that biotic stress was caused by millipedes. Millipedes of the species Omopyge sudanica were responsible for the loss of up to 84% of the sweet potato cuttings if the crop was planted early in the first rainy season. During bulking hardly any damage was inflicted on the storage roots. When the tubers were stored ‘in-ground on plants’ during the dry season, millipedes in combination with other insect pests affected up to 86% of the tubers at the onset of the rains of the following growing season. Data on groundnut and maize were taken on plots where in the previous season sweet potato had been grown. Early in the first rainy season, O. sudanica also caused damage in germinating groundnut, causing plant losses of 12–29%. Maturing groundnut seeds were affected for 39%. Millipede damage in germinating maize seeds in the first and second rainy seasons amounted to 34% and 29%, respectively. The species O. sudanica, Spirostreptus ibanda and Tibiomus spp. cfr. ambitus were found in the vicinity of the maize seeds but were only found feeding on them during the second rainy season. More research is needed to quantitatively assess economic damage to crop production caused by millipedes.

Effect of temperature, soil moisture content and type of cutting on establishment of sweet potato cuttings

Effective rooting is essential for successful crop establishment from cuttings. The objective of this study was to determine the effect of temperature and soil water content on the root and shoot growth during the early establishment of sweet potato cuttings. Root growth and development were examined in a phytotron at four temperatures (20, 24, 28 and 32 °C constant) and with four types of cuttings (3 node cutting vertically planted, 3 node cutting planted upside down, 3 node cutting horizontally planted and 1 node cutting planted horizontally). The cuttings were allowed to establish and grow for three weeks. The highest total root length (3.59 m plant-1) was recorded in the 24 °C growth chamber and was significantly longer than the roots from the other temperature treatments. The highest root dry mass (0.22 g plant-1), shoot dry mass (1.7 g plant-1), leaf area (578 cm2) and total dry mass (2.0 g plant-1) were also obtained from the 24 °C growth chamber. The three node cuttings planted vertically produced the longest total root length of 3.66 m plant-1 which was significantly longer than those of the other cutting types. The highest root dry mass, shoot dry mass, leaf area, vine length, leaf number, and total dry mass were also obtained from the vertically planted three node cuttings. To determine the response to soil moisture content, cuttings were sealed and allowed to establish and grow in plastic bags containing sandy soil at 100, 80, 60 and 40% of field water capacity. After 12 and 20 days in a growth chamber at 28 °C the plants were harvested. The 80% of field capacity moisture regime was found to be the optimum soil moisture content for sweet potato root growth. With the soil water content at field capacity and at 40% of field capacity root development was somewhat suppressed. The results illustrated the capacity of sweet potato cuttings to establish successfully under a range of ambient temperatures and soil moisture contents.

Regulation of tuber formation and ADP-glucose pyrophosphorylase (AGPase) in sweet potato ( Ipomoea batatas (L.) Lam.) by nitrate

The relationship between nitrate fertilization and tuber-bulking inroots from single-leaf explants was examined to clarify the mechanism of tuberformation. Cuttings of sweet potato leaves were grown on a medium containing 1,10, 30, and 50 mM nitrate and analyzed with regard tomorphologicaland biochemical traits. The cuttings grown on higher concentrations (≥10mM) showed inhibited root growth, with no apparent effect on leafgrowth or root length. The roots accumulated starch in a medium containing alower nitrate concentration (≤10 mM). Under this culturecondition, both the ADP-glucose pyrophosphorylase (AGPase) transcript level andthe starch content in the root decreased, while there was no decrease in thestarch content in the leaf. The greater AGPase transcript level in rootsgrowingwith a higher nitrate concentration (≥10 mM) might be caused bynitrogen-mediated signalling and/or changes in the levels of starch metabolism.Starch synthesis via AGPase and cell proliferation may work together for tuberformation in sweet potato root.

336 A Comparison of Virus-free Versus Infected Sweetpotato Transplants for Cutting Propagation

Production of disease-free sweetpotato [Ipomoea batatas (L.) Lam.] transplants is of major importance to certified and foundation seed programs and producers. Sweetpotato roots are traditionally planted and cuttings are harvested from propagation beds. The objective of this study was to investigate the efficiency of producing cuttings in nursery containers. Virus-tested and virus-infected `Beauregard' sweetpotato transplants were harvested from planting beds for the purpose of producing cuttings for transplants. Cuttings were established in 3.7-L plastic nursery containers filled with 100% pine bark amended with either low, medium, or high rates of Osmocote 14-14-14 and dolomitic lime. Resulting transplants produced a greater number of cuttings and greater plant biomass with higher fertilizer rates. Increasing fertilizer rates also had a positive effect on cutting production and biomass. Dry weight and stem growth were similar for both virus-infected and virus-tested transplants following first and second harvests. Producing foundation cuttings in nursery containers filled with a pine bark medium proved to be an efficient method of increasing virus-tested sweetpotato cuttings.

Root System Development of Cassava and Sweetpotato during Early Growth Stage as Affected by High Root Zone Temperature

Root zone temperature (RZT) is an important factor that affects the establishment of crops in the field. This study was conducted to determine the effect of high RZT on the root system development of cassava and sweetpotato and to assess the response of each root system component of cassava and sweetpotato to high RZTs. Cassava and sweetpotato are widely grown crops in soils that are prone to reach a high temperature especially during the dry season. The plant root system was the primary object of investigation in this study. Cassava and sweetpotato cuttings were grown in pots for 20 days in a growth chamber where two different soil temperature regimes were maintained : 40°C (high RZT) and 25°C (normal). High RZT significantly decreased the total length of the adventitious roots (ARs) and the number and total length of the first order lateral roots (LRs) in both cassava and sweetpotato. Reduction in these root growth parameters was greater in the latter than in the former. High RZT caused a marked increase in the number of the second order LRs in sweetpotato and tended to enhance the formation of the third order LRs. Under high RZT, in cassava, a higher proportion of the total number of ARs and the first order LRs, and thus, a greater fraction of the total root length came from the lower nodes of the cuttings that were buried deep in the soil at planting. In sweetpotato, a greater proportion of the total number and total length of the ARs and the first order LRs was observed in the nodes of the cuttings that were buried closer to the soil surface than those buried deeper. An opposite trend was evident in both cassava and sweetpotato grown under a normal RZT. In the screenhouse experiment where plants were grown for 12 days, root growth of cassava was significantly reduced by the high RZT that prevailed when the soil was not covered with mulch materials. The root development in the mulched soil was similar to that under normal RZT in the growth chamber.

Comparison of the rooting ability of virus infected and virus-free cuttings of sweet potatoes (Ipomoea batatas Poir.) and an anatomical comparison of the roots

SummaryThe rooting abilities of the filamentous virus infected and the virus-free cuttings of sweet potato (Ipomoea batatas Poir.) were compared, with an anatomical comparison of the root. The diameters of the pith and the vascular bundle cylinder at the node of the virus-free cutting were larger than in those of virus infected ones. Thicker and more vigorous roots were initiated in the virus-free cutting. The diameter of the central cylinder and the thickness of the cortical layer of the root were larger in the virus-free cutting than in the virus infected one. Larger and more numerous vessels developed, and larger and more distinct meristematic tissues surrounding the protophloem poles also developed in a fan form in the root of the virus-free cutting. The weight of the leaf and stem of the plant 80.d after planting in the field were larger in the virus-free cutting than in the virus infected cutting. From these results, the following assumptions on roots in the virus-free cutting can be made. Thicker roots with larger vessels and thicker meristematic tissues develop in the virus-free cutting because the meristematic activity is high in the tissues in the vicinity of the vascular bundle cylinder at the node, due to the recovery of normal physiological function by removal of the virus. There are fewer roots in the virus-free cutting because the smaller total area of the root is sufficient to absorb the nutrient elements owing to superior development of the vessels and meristematic tissues in the root. In the field, the larger weight of the leaf and stem in the virus-free cutting is caused by the high absorption ability of nutrient elements from the root.

Forced Ventilation Micropropagation System for Enhancing Photosynthesis, Growth, and Development of Sweetpotato Plantlets.

A forced ventilation micropropagation system was developed, and with this system, single-node leafy stem cuttings of sweetpotato (Ipomoea batatas (L.) Lam., cv. Beniazuma) were cultured on cellulose plugs or vermiculite used as supporting materials with Murashige and Skoog (1962) nutrients but without sugar, i.e., photoautotrophically. The inlet CO2 concentration of the system was 1 500μmol mol-1 and the photosynthetic photon flux on the culture shelf was 150μmol m-2 s-1. The net photosynthetic rate and dry mass of sweetpotato plug plantlets from the forced ventilation treatment on day 22 were 30-40 times and 4-6 times greater, respectively, than those of the plantlets grown under the conventional, photomixotrophic micropropagation system with natural ventilation and gelled agar medium containing sugar.

Biocompatibility of Sweetpotato and Peanut in a Hydroponic System

'Georgia Red' peanut (Arachis hypogaea L.) and TU-82-155 sweetpotato [Ipomoea batatas (L.) Lam] were grown in monocultured or intercropped recirculating hydroponic systems in a greenhouse using the nutrient film technique (NFT). The objective was to determine whether growth and subsequent yield would be affected by intercropping. Treatments were sweetpotato monoculture (SP), peanut monoculture (PN), and sweetpotato and peanut grown in separate NFT channels but sharing a common nutrient solution (SP-PN). Greenhouse conditions ranged from 24 to 33 degrees C, 60% to 90% relative humidity (RH), and photosynthetic photon flux (PPF) of 200 to 1700 micromoles m-2 s-1. Sweetpotato cuttings (15 cm long) and 14-day-old seedlings of peanuts were planted into growth channels (0.15 x 0.15 x 1.2 m). Plants were spaced 25 cm apart within and 25 cm apart between growing channels. A modified half-Hoagland solution with a 1 N: 2.4 K ratio was used. Solution pH was maintained between 5.5 and 6.0 for treatments involving SP and 6.4 and 6.7 for PN. Electrical conductivity (EC) ranged between 1100 and 1200 microS cm-1. The number of storage roots per sweetpotato plant was similar for both SP and SP-PN. Storage root fresh and dry mass were 29% and 36% greater, respectively, for plants in the SP-PN treatment than for plants in the SP treatment. The percent dry mass of the storage roots, dry mass of fibrous and pencil roots, and the length-to-diameter ratio of storage roots were similar for SP and SP-PN sweetpotato plants. Likewise, foliage fresh and dry mass and harvest index were not significantly influenced by treatment. Total dry mass was 37% greater for PN than for SP-PN peanut plants, and pod dry mass was 82% higher. Mature and total seed dry mass and fibrous root dry mass were significantly greater for PN than for SP-PN plants. Harvest index (HI) was similar for both treatments. Root length tended to be lower for seedlings grown in the nutrient solution from the SP-PN treatment.

Apparent absence of viruses in most symptomless field‐grown sweet potato in Uganda

SummarySymptomless sweet potato (Ipomoea batatas) plants obtained from farmers' fields in each of the main sweet potato growing regions of Uganda were tested by nitro‐cellulose membrane enzyme‐linked immunosorbent assays (NCM‐ELISA) for sweet potato feathery mottle virus (SPFMV), sweet potato mild mottle virus (SPMMV), sweet potato chlorotic fleck virus (SPCFV), sweet potato latent virus (SPLV), C‐6 virus (C‐6) and sweet potato caulimo‐like virus (SPCa‐LV). Most of the plants tested gave negative reactions in all NCM‐ELISA, only c. 5% giving positive reactions to SPFMV and c 1% to SPMMV or SPCFV. Graft inoculations of cuttings from symptomless sweet potato plants, obtained either at Namulonge Agricultural and Animal Production Research Institute (NAARI) or from farmers' fields, onto seedlings of the near‐universal indicator plant for sweet potato viruses, Zpomoea setosa, caused symptoms in c. 15% of indicator plants; in all such cases, SPFMV alone was identified by NCM‐ELISA. Supplementary tests, involving further grafting of sweet potato to I. setosa seedlings or grafting sweet potato plants themselves with sweet potato sunken vein virus (SPSVV), which in the presence of SPFMV causes sweet potato virus disease (SPVD), confirmed the absence of infection in sweet potato cuttings which had not caused symptoms on I. setosa in the initial graft test. Possible mechanisms explaining the prevalence of virus‐free sweet potato plants in farmers' fields are discussed.

Rapid Production of Sweetpotato Cuttings under Controlled Environment: CO2 Enrichment and Cutting Preparation Affected the Growth and Production Rates

Sweetpotato [Ipomoea batatas (L.) Lam.] has been cultivated and recognized as an important crop in many countries, including Japan. Leafy node cuttings originated from virus-free, micropropagated mother plants are widely used for propagation of sweetpotato. In the present study, plant growth and cutting propagation rates as affected by atmospheric CO2 concentration and cutting preparation (single- or multi-node cutting) were investigated. Cuttings of `Beniazuma' sweetpotato were hydroponically cultured with or without carbon dioxide enrichment (CDE) under controlled greenhouse environment. Carbon dioxide concentration inside the greenhouse was either 1000 μmol·mol–1 with CDE or 300 μmol·mol–1 without CDE. Air temperature and relative humidity were maintained at 30 ± 1C and 80 ± 10%, respectively. Growth and development rates of the cuttings were analyzed on 20th day after start of the experiment. CDE enhanced fresh and dry weights per cutting. Propagation parameters (fresh and dry weights per single mother vine, leaf development rate, and cutting propagation rate) were greater when started from single-node cuttings than from multi-node cuttings, either with or without CDE. Shoot tip removal reduced leaf development and cutting propagation rates, but it did not affect the fresh and dry weights.

Yield of Sweetpotato Cuttings Is Not Influenced by Shoot Apex or Polarity

Cuttings taken from the vines of established sweetpotatoes maybe used to establish field plantings (Edmond, 1971). These vine cuttings are cut from stock plants five or six nodes below the shoot apex in 20to 30-cm sections and then cut serially along the length of the same vine. The acropetal end should be oriented aboveground for transplanting. Since sweetpotato vines grow prostrate on the soil surface, leaves may not always be oriented in the acropetal direction toward the shoot apex. Therefore, leaf orientation is not an accurate indicator of polarity for sweetpotato vine cuttings, but the shoot apex and axillary buds assist in identifying shoot polarity. However, absence of the shoot apex hampers rapid determination of polarity, and cuttings must be closely examined for orientation of the axillarv buds to ensure that they are planted in an upright position. Such difficulty often results in some cuttings being transplanted with a reversed polarity (inverted) in commercial sweetpotato fields. In a previous study, removing the shoot apex increased vine branching but did not influence U.S. #1 or total marketable yield (Hall, 1987). The combined influence of the shoot apex and polarity of cuttings on sweetpotato root yield has not been described. The objective of this work was to determine the influence of the shoot apex and polarity of transplanted vine cuttings on sweetpotato root yield.

Induction of Expression of Genes Coding for Sporamin and β-Amylase by Polygalacturonic Acid in Leaf-Petiole Cuttings of Sweet Potato

Sporamin and beta-amylase are two major proteins of tuberous storage root of sweet potato (Ipomoea batatas) and their accumulation can be induced concomitantly with the accumulation of starch in leaves and petioles by sucrose (K Nakamura, M Ohto, N Yoshida, K Nakamura [1991] Plant Physiol 96: 902-909). Although mechanical wounding of leaves of sweet potato only occasionally induced the expression of sporamin and beta-amylase genes, their expression could be reproducibly induced in leaf-petiole cuttings when these explants were dipped in a solution of polygalacturonic acid or chitosan at their cut edges. Polygalacturonic acid seemed to induce expression of the same genes coding for sporamin and beta-amylase that are induced by sucrose. Because polygalacturonic acid and chitosan are known to mediate the induction of wound-inducible defense reactions, these results raise an interesting possibility that beta-amylase, in addition to sporamin, may have some role in the defense reaction. Expression of sporamin and beta-amylase genes could also be induced by abscisic acid, and this induction by abscisic acid, as well as induction by polygalacturonic acid or sucrose, was repressed by gibberellic acid. By contrast, methyl jasmonate did not cause the significant induction of either sporamin or beta-amylase mRNAs. Induction of expression of sporamin and beta-amylase genes by polygalacturonic acid or sucrose was inhibited by cycloheximide, suggesting that de novo synthesis of proteins is required for both of the induction processes.

Establishment of sweet potato stem cuttings as influenced by size, depth of planting, water stress, hormones and herbicide residues for two genotypes

A set of short-term experiments on the establishment of sweet potato stem cuttings was conducted under greenhouse conditions and terminated at about 30 days after transplanting. The following recommendations can be made. When drought stressed, a stem length of 30 cm (versus 15, 20 and 25 cm) with 10–15 cm of the stem covered by soil produced the most vigorous growth, an important asset when early season weed competition is evident and when rapid ground cover is important. The advantages of dipping cuttings into a dissolved root hormone were cultivar dependent, but pre-rooted cuttings were of no benefit to either cultivar in terms of survival and growth. During establishment, drought significantly reduced the stem weight and leaf weight and area, and similar but non-significant trends were also evident for root number and weight.

Sucrose-Induced Accumulation of β-Amylase Occurs Concomitant with the Accumulation of Starch and Sporamin in Leaf-Petiole Cuttings of Sweet Potato

beta-Amylase of sweet potato (Ipomoea batatas L.), which constitutes about 5% of the total soluble protein of the tuberous root, is absent or is present in only small amounts in organs other than the tuberous roots of the normal, field-grown plants. However, when leaf-petiole cuttings from such plants were supplied with a solution that contained sucrose, the accumulation of beta-amylase was induced in both leaf and petiole portions of the explants. The sucrose-induced accumulation of beta-amylase in leaf-petiole cuttings occurred concomitant with the accumulation of starch and of sporamin, the most abundant storage protein of the tuberous root. The accumulation of beta-amylase, of sporamin and of starch in the petioles showed similar dependence on the concentration of sucrose, and a 6% solution of sucrose gave the highest levels of induction when assayed after 7 days of treatment. The induction of mRNAs for beta-amylase and sporamin in the petiole could be detected after 6 hours of treatment with sucrose, and the accumulation of beta-amylase and sporamin polypeptides, as well as that of starch, continued for a further 3 weeks. In addition to sucrose, glucose or fructose, but not mannitol or sorbitol, also induced the accumulation of beta-amylase and sporamin, suggesting that metabolic effects of sucrose are important in the mechanism of this induction. Treatment of leaf-petiole cuttings with water under continuous light, but not in darkness, also caused the accumulation of small amounts of these components in the petioles, probably as a result of the endogenous supply of sucrose by photosynthesis. These results suggest that the expression of the gene for beta-amylase is under metabolic control which is coupled with the expression of sink function of cells in the sweet potato.

Isolate Selection and Phosphorus Interaction of Vesicular‐Arbuscular Mycorrhizal Fungi in Biomass Crops

AbstractIndustrial sweet potato [Ipomoea batatas (L.) Lam, cv. White Star] and Napiergrass (Pennisetum americana × P. purpureum hybrid triploid PI 300086) have good potential for biomass energy systems. The objective of this research was to evaluate vesicular‐arbuscular mycorrhizal (vam) fungi for their ability to provide P to these crops across a range of soil P. To select effective vam fungi, cuttings of sweet potato were inoculated with nine isolates of fungi and were grown in soil with no P addition. Plants were evaluated after 3, 7, and 11 wk. To determine the range of soil P where these crops respond to vam fungi, experiments were conducted with sweet potato and Napiergrass, using at least two vam fungi and five P additions ranging from 0 to 198 mg P kg−1 of soil. Plants were evaluated after 4 and 16 wk. Sweet potato response to vam fungi ranged from growth enhancement to growth depression, compared to control plants. Both inter‐ and intraspecific fungal variation was observed. Total biomass production at 11 wk was correlated positively with root colonization at 3 wk, but not at 7 or 11 wk. Mycorrhizal dependency for both biomass plants decreased with P addition; nonetheless, growth was greater for plants inoculated with vam fungi and with up to 23 mg added P kg−1. The apparent ineffectiveness of the indigenous vam fungi, and the responsiveness of these biomass crops to selected vam fungi within a practical range of fertilizer P, may provide an opportunity for inoculation.

Effects of abscisic acid on rooting stem cuttings of sweet potato in open top chambers under enriched CO2 environment

Ten centimeter long stem cuttings of sweet potato (Ipomoea batatas L. cv. Georgia Jet) with intact apex and leaves were cultured in distilled water as well as in varying concentrations of abscisic acid (ABA) in open top chambers at 364, 438 and 666 cm3 m{-3}CO2. Low concentration of ABA promoted rooting and elongation of roots at 364 cm3 m{-3} CO2 while rooting was suppressed at enriched levels of CO2. However, biomass production in shoots and roots was higher in 666 than in 364 cm3 m-3 CO2.

Selection of Sweet Potato For Tolerance to Aluminum Toxicity: Screening Procedures and Field Test

Abstract The effects of varying levels of Al on fibrous root growth variables of vine tip cuttings of sweet potato [Ipomoea batatas (L.) Lam] were tested in a quartz-sand medium in the greenhouse. A significant negative relationship between Al level and root growth was noted. Root weight was increased slightly on some clones at Al levels up to 250 μM. Aluminum levels > 500 μM considerably reduced root growth. Root lengths relative to the control were used in the screening of 379 sweet potato clones and in the preliminary identification of 60 tolerant and 55 sensitive clones. The tolerant clones had greater relative root length than the sensitive ones. In a field study, no significant differences in marketable root yield were noted between lime treatment (pH 5.4) and sulfur treatment (pH 4.2). The sulfur treatment, however, increased nonmarketable yield. The sensitive clones produced greater nonmarketable yield than the tolerant ones. A negative relationship between Al tolerance and yield in nonstress condition was indicated; tolerant clones generally yielded less than sensitive ones in nonstress field tests. Root lengths in the no-Al treatment in the greenhouse were significantly correlated with the marketable root yield and number in the limed field treatments.