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Melvin R. Hall

Immersion of sweetpotato [Ipomoea batatas (L.)] storage roots in low concentration (5 and 50 mg·liter-1) of gibberellic acid (GA) in solutions of benzyl adenine plus GA4+7 increased early but not total plant production from bedded roots of `Georgia Jet' and `Jewel'. Immersion in 0.5 and 1 mg·liter-1 solutions of GA3 increased early plant production from `Georgia Jet'. Neither weight nor visual appearance of the harvested plants nor root yield from transplants were influenced by gibberellin treatments of the bedded roots.

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L. J. Kushman and D. T. Pope

Abstract

Recent studies showed that at harvest sweetpotato storage roots contain as much as 10 milliliters of intercellular space per 100 milliliters of root; during storage intercellular space increases to the extent that it becomes visible and is classified as pithiness or internal breakdown (1). A preliminary report shows that by accounting for the intercellular space tissue specific gravity values can be computed and correlated with drymatter content in much the same manner as for Irish potatoes (2). At harvest intercellular space for each of four varieties was relatively constant for a given variety and differed significantly among varieties (4).

Open access

Adisak Sajjapongse, Mei-Huey Wu, and Yu-Chi Roan

Abstract

High temperature during August plantings of sweet potato [Ipomoea batatas (L.) Lam.] reduced the number of storage roots/plant, increased top weight, and gave low yield. November planting, when the temperature was relatively low, had no effect on root formation but resulted in small roots. Yields were related to the accumulated temperature of the first 60 days after planting (DAP) and the relationship was quadratic. Regression analysis revealed that the highest yield (15.3 t·ha–1) in 1981–82 was obtained when the mean daily temperature of the first 60 DAP was 22.4°C. Analogous data for 1983–84 were 17.7 t·ha–1 and 23.1°.

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L. A. Chang and S. J. Kays

Abstract

Respiration of sweet potato roots was significantly depressed by low oxygen concentrations from 5 to 15% compared to 20% O2, but respiration at 2.5% O2 was high. Total sugar accumulated with low oxygen (2.5 and 5.0%) storage. Protopectin was low in roots stored at low O2 concentrations but water soluble pectin was not significantly affected. Physical parameters Ew and δf the storage roots were high when stored at low O2 concentrations. Ey and Ef were not significantly affected. Ew was correlated with total sugar (r = 0.79).

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L. E. Scott and J. C. Bouwkamp

Abstract

The concentration and total content of P, K, Ca, Mg, N, Fe, Mn, and B in storage roots and in vines of sweet potatoes [Ipomoea batatas (L.) Lam.] was followed for a 14 week period beginning 2 months after planting. The concentration of N, P, K, Mn, and Mg in the vines and N, P, and K in the roots decreased slightly during the period. Other elements showed no definite seasonal trends. Total uptake by the vines showed little change after the second sampling period

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P. J. Ndolo and E. G. Rhoden

Root growth of sweet potato [Ipomoea batatas (L) Lam.] cvs `TI-82-155', `Centennial' and `Rojo Blanco' in coarse fritted clay soil, was investigated under greenhouse conditions. The sweet potato cultivars were harvested at 41 and 82 days after planting. Dry weight of fibrous roots of all cultivars were similar at day 41. Fibrous root weight of `Rojo Blanco' increased by 5% while those of the other cultivars increased by 168%. Mean fibrous root length per centimeter depth was not significantly different among cultivars. Although fresh weight of storage roots of `Rojo Blanco' was significantly lower than those of the other cultivars, their dry weights were similar. `TI-82-155' and `Rojo Blanco' had fewer storage roots compared to the other cultivars, however, storage root length of `TI-82-155' or `Rojo Blanco' was greater than that of `Georgia Jet' or `Centennial'. Length to diameter ratio of the storage root of `Rojo Blanco' was significantly greater than that of `TI-82-155' and `Georgia Jet'.

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Yan Wang and Stanley J. Kays

The sweetpotato weevil is the single most critical insect pest of the sweetpotato worldwide. While male weevils can be lured to traps using a synthetic female pheromone, crop losses are not adequately reduced since damage is caused by the larvae arrising from eggs laid by female weevils in the storage roots. Identification of a female attractant could greatly enhance the control of the insect. The leaves and storage roots are known to emit volatiles that attract the female and in the following tests, we demonstrate that feeding by female weevils stimulates the synthesis of a volatile attractant which attracts additional females to the root. Undamaged, artificially damaged, and female weevil feeding damaged periderm were tested in dual-choice and no-choice olfactometers. Volatiles from feeding damaged roots were significantly more attractive than undamaged and artificially damaged roots. To test whether the volatile attractant was of weevil or root origin, volatiles were collected in MeCl2 after removal of the weevils and fractionated on a megabore DB-1 capillary column using a GC fitted with a TC detector. Fractions were collected from the exit port and their activity index (AI) determined using dual choice and no choice olfactometry. The active fraction was ascertained and active components identified via GC-MS.

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D.R. La Bonte, A.Q. Villordon, J.R. Schultheis, and D.W. Monks

The influence of a black polyethylene tunnel cover (BTC) was evaluated for its effect on quantity and quality of sweetpotato [Ipomoea batatas (L.) Lam.] transplants in plant beds in Louisiana and North Carolina. Use of BTC increased production of `Beauregard' transplants from 63% to 553% in comparison with the bare ground control. `Jewel' was less responsive; BTC treatments increased transplant production by at least 48% in Louisiana over the bare ground control, but no increase was observed in North Carolina. Individual transplant weight was at least 34% less in BTC treatments than in the control. The first harvest of cuttings in BTC beds was at least 14 days prior to that in control beds. Transplant quality was assessed as yield of storage roots in repeated trials that extended throughout the normal growing season. Yield of storage roots was not affected by BTC in early season plantings, but was frequently lower for BTC treatment transplants in middle and late season plantings. We therefore do not recommend this method as a means of increasing sweetpotato plant production from bedded roots.

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P. J. Ndolo and E. G. Rhoden

Root growth of sweet potato [Ipomoea batatas (L) Lam.] cvs `TI-82-155', `Centennial' and `Rojo Blanco' in coarse fritted clay soil, was investigated under greenhouse conditions. The sweet potato cultivars were harvested at 41 and 82 days after planting. Dry weight of fibrous roots of all cultivars were similar at day 41. Fibrous root weight of `Rojo Blanco' increased by 5% while those of the other cultivars increased by 168%. Mean fibrous root length per centimeter depth was not significantly different among cultivars. Although fresh weight of storage roots of `Rojo Blanco' was significantly lower than those of the other cultivars, their dry weights were similar. `TI-82-155' and `Rojo Blanco' had fewer storage roots compared to the other cultivars, however, storage root length of `TI-82-155' or `Rojo Blanco' was greater than that of `Georgia Jet' or `Centennial'. Length to diameter ratio of the storage root of `Rojo Blanco' was significantly greater than that of `TI-82-155' and `Georgia Jet'.

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A. Golmirzaie, D.P. Zhang, L. Nopo, C.A. Newell, A. Vera, and F. Cisneros

Euscepes postfasciatus is one of the most important sweetpotato pests in the South Pacific, Caribbean basin, and some countries of Central and South America. Development of host resistance will greatly improve the effects of integrated pest management (IPM) for this pest. Ten transgenic clones of `Jewel' sweetpotato with cowpea trypsin inhibitors and snowdrop lectin, developed by Axis Agri. Genetics, Ltd., were assayed for weevil resistance using a no-choice bioassay. A replicated experiment was conducted in the screenhouse. Five storage roots from each clone were infested with five pairs of adults. Non-transformed `Jewel' was used as a check. Resistance was assessed 60 days after infestation by estimating the percentage of internal damage and the weevil population in the storage roots. A five-grade damage index was recorded. The experiment was repeated twice. Significant enhancement of resistance was found in the transgenic clones. Clone CTI-13 with cowpea trypsin inhibitor and clone PCG-7 with both cowpea trypsin inhibitor and snowdrop lectin demonstrated moderate resistance to E. postfasciatus, whereas the non-transformed `Jewel' was susceptible. This result shows that resistance to Euscepes postfasciatus can be achieved through genetic transformation.