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Kenji Katayama, Katsumi Komaki, and Seiji Tamiya

Near infrared analysis was used to predict the starch, moisture, and sugar content in sliced fresh sweetpotato [Ipomoea batatas (L.) Lam.] storage roots. Samples were collected in each of three growing years. The best calibration equation for starch from combined samples (1989 to 1991) showed a multiple correlation coefficient (R) of 0.949, a standard error of calibration (sec) of 2.01, and a standard error of prediction (sep) of 1.91. The R, sec, and sep for moisture and sugar were 0.930, 1.85, and 2.00, and 0.837, 1.30, and 1.21, respectively. Calibrations based on samples from a given year adequately predicted the variables but could not account for variances introduced by samples from other years. Multiyear calibrations based on several years of data adequately predicted starch and moisture content in root slices. Thus, multiyear calibrations with annual bias adjustments can be applied to screening sweetpotato breeding germplasm for these two variables.

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Lewis W. Jett and Timothy P. Talbot

A cultural practice that can modify and conserve the soil environment is needed in sweetpotato [Ipomoea batatas (L.) Lam.] production. The objective of this research was to evaluate conventional and conservation tillage of sweetpotato with four cover crop species (fallow, ryegrass, rye, and wheat). The cover crops were seeded in late Oct. 1995, and the sweetpotato transplants (`Beauregard') were transplanted at two dates the following spring (May and June). Conservation tillage significantly lowered soil temperature (10 cm depth) during storage root initiation and development. Moreover, each cover crop significantly reduced weed emergence and soil erosion. The ryegrass conservation tillage treatment significantly increased marketable yield of sweetpotato in the first planting date, while rye and wheat performed equally well in the second planting date. In the second planting date, white grub (Phyllophaga ephilida Say) injury to storage roots was significantly higher in the conservation tillage treatments. However, conservation tillage seems to be a viable alternative to the conventional method of sweetpotato production.

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C. Stevens, V. A. Khan, J. L. Lu, C. L. Wilson, E. Chalutz, M. K. Kabwe, and Z. Haung

Jewel sweetpotato storage roots previously treated with ultraviolet (UV–C) light and then stored for 30 days before artificial inoculation with Fusarium solani showed increased resistance to Fusarium root rot; as indicated by reduced lesion size, the rate of decay development of rotted tissues. There was a hormetic relationship between the incidence of Fusarium root rot and UV–C doses. The optimum dose of UV which reduced Fusarium root rot was 3.6× 104 ergs/mm2. Exposure of sweetpotato to UV–C doses promoted phenylalanine ammonia–lyase (PAL)4 production with the maximum PAL activity occurring at 3.6×104 ergs/mm2. Crude extracts from UV–C treated sweetpotatoes reduced germination, germ tube elongation and growth of F. solani when compared to untreated extracts.

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J. C. Bouwkamp

Abstract

Response to mid-day wilting (dehydration avoidance) among sweet potato [Ipomoea batatas L. (Lam)] genotypes is a consistent trait within and among years. This response is significantly related to storage root dry weight and net photosynthesis in most years. The relationship is more obvious among relatively high-yielding clones or when data are obtained over several years. Reduced mid-day wilting increases yield in high-yielding genotypes through increased net photosynthesis and increased partitioning of assimilates to storage roots. Increased storage root dry weight is also related to the percentage of water in the vines at near full-turgor through increased partitioning to roots and reduced mid-day wilting. Wilting response and vine moisture together account for nearly 25% of the variation in yield of high-yielding clones tested over 5 years with irrigation.

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A.A. Trotman, W.A. Hill, D.G. Mortley, P.P. David, and P.A. Loretan

The effect of inoculation with Azospirillum brasilense strain Cd on mineral concentration in sweetpotato, [Ipomeo batatas (L) Lam cv. TI-155] tissue and ionic composition of plant nutrient solution was investigated in a greenhouse study. In the field, inoculation of sweetpotato with Azospirillum spp. has been reported to enhance. sweetpotato yield. In this study, 48-h old broth cultures were used as inoculum at a population density of approx. 1 × 108 cfu/ml. The inoculum (0.20 L) was added to the reservoirs containing 30.4 L of a modified half Hoagland's plant nutrient solution at 28 days after the start of the experiment Results indicate that percent total nitrogen in sweetpotato foliage tended to be higher for the inoculated fibrous mat than in the fibrous mat for non-inoculated plants. The percent total nitrogen in storage roots for the non-inoculated treatment tended to be higher than in storage roots for inoculated plants. Inoculation resulted in a slight increase in foliar phosphorus concentration but had no effect on phosphorus concentration in sweetpotato storage and fibrous root samples. Inoculation tended to reduce foliar calcium concentration. Magnesium concentration in leaf tissue was not influenced by inoculation. Foliar potassium concentration tended to increase slightly. The effect of inoculation on potassium concentration in sweetpotato root tissue was not well-defined; potassium concentration tended to be higher in fibrous root tissue for the inoculated treatment. But in storage root tissue, potassium concentration was higher for the non-inoculated treatment than for the inoculated treatment. Inoculation did not affect foliar concentrations of any of the micronutrients measured. This study indicates no effect of inoculation on ionic strength of nutrients in solution reservoirs.

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Scott Aker and William Healy

Alstroemeria `Regina' and A. `Orchid' Linn. plants were grown in rhizotrons to facilitate non-destructive observation of shoot, rhizome, and storage root growth. In plants grown at 21/11 C or 21/21 C day/night temperatures under either 8 hr night interruption or an 8 hour short days, storage root growth was favored by cool (11 C) night temperatures and long days. The seasonal patterns of storage root and rhizome growth were inversely related to the seasonal pattern of shoot growth. Growth of shoots and rhizomes followed a cyclic pattern. The cycles of shoot and rhizome growth were in phase with each other until the plants resumed vegetative growth due to high soil temperature. At this point, the cycles of shoot and rhizome growth were shifted out of phase with each other. Thinning shoots by 60% resulted in delay and damping out of the peak of storage root growth; the cyclic growth of storage roots was disrupted when plants were thinned by 60% such that the cycles of active storage root growth were delayed by 1 week.

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Melvin R. Hall

`Red Jewel' sweetpotato [Ipomoea batatas (L.)] roots were cured [32 ± 1C, 85% ± 5% relative humidity (RH)] for 7 days immediately after harvest and cured for O. or 8 additional days before being stored (16 ± 1C, 85% ± 5% RH). Midway through storage, roots were heated (32 ± 1C, 85% ± 5% RH) for 0, 2, 4, 6, 8, 10, 12, or 14 days and placed back into storage. Before being bedded, roots were presprouted (32 ± 1C, 85% ± 5% RH) for O or 8 days. Plant emergence was accelerated with extended curing or presprouting and with increased midstorage heating duration. Early plant production increased with increasing duration of midstorage heating of roots not subjected to extended curing or presprouting. Eight days of extended curing eliminated response to midstorage heating; but, with 8 days of presprouting, a quadratic response to midstorage heating peaked at ≈ 8 days. However, when combined with midstorage heating, presprouting had more of an effect than extended curing on early plant production. Briefly extending curing, midstorage heating, and presprouting each independently increased the cumulative number of midseason plants, but only presprouting influenced total plant production. Treatments did not influence deterioration of bedded roots or number of sprouts <20 cm produced during 10 weeks of harvest.

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Jonathan R. Schultheis and Dennis E. Adams

Boron has been used to overcome the disorder blister in varieties such as `Jewel'. `Hernandez' is an attractive, good-yielding variety with uniform shape that will consistently pack out at 80% to 90%. Over time in storage, however, roots develop blister-like symptoms, rendering roots unmarketable for fresh market. Our objective was to evaluate the effect of different B rates and application times on the yield and quality of `Hernandez' roots. Rates were varied up to 2.24 kg actual B/ha 6 days after planting, while various soil and foliar application times (6, 34, and 69 days after planting) were evaluated at 1.12 kg·ha–1. In 1994, three row plots were arranged in a randomized complete block design and replicated four times. Planting was on a deep sand to maximize the effect of the B carrier Solubor. Roots were harvested, graded, and weighed 120 days after planting and storage roots evaluated for blister-like symptoms in Mar. 1995. No significant differences in yield were attributed to B rate or application method. Blister-like symptoms were more severe when no B was applied; however, application of B did not eliminate symptoms, as most roots had the blister-like appearance. Boron application did not solve the problem, but symptoms were less apparent when some B was applied.

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A.Q. Villordon, J.W. Franklin, and W. McLemore

This report summarizes the results of irrigation studies conducted from 2000 to 2005 at the Sweet Potato Research Station, Chase, La. These studies investigated the role of various scheduling methods, soil moisture measurement devices, and irrigation delivery methods in sweetpotato production. The studies indicate that 15 to 20 inches of total rainfall and supplemental irrigation is required to produce 400 to 525 bu/acre of US#1 storage roots in Beauregard. Supplemental irrigation can be scheduled based on this benchmark, potentially reducing over-irrigation during dry periods. We have also found that during dry periods, irrigating every furrow can bring about 50% difference in US#1 yield vs. supplying irrigation to alternate furrows. During growing seasons characterized by optimum rainfall patterns, we did not detect any response in US#1 yield to various irrigation treatments. We evaluated several moisture measurement devices including granular matrix sensors, evaporation pan, time domain reflectometry (TDR)-based instrument, and tensiometers. We found the TDR-based device easy to use and convenient in terms of its portability. Based on studies conducted in 2001 and 2002, this device demonstrated potential as a management tool in sweetpotato production. For instance, a management allowable deficit (MAD) of 25% available moisture as measured using the TDR-based device can potentially result in the same yield as weekly irrigation and a MAD of 50% available moisture. When used properly, irrigation scheduling can reduce over-irrigation and contribute to overall efficiency in the use of production inputs.

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Melvin R. Hall

`Red Jewel' sweetpotato [Ipomoea batatas (L.) Lam.] roots were cured [32 ± 1C, 85% relative humidity (RH)] for 7 days immediately after harvest and then subjected to selected single or combined applications of additional curing, midstorage heating, and presprouting not to exceed 21 days. Extended curing was applied for 0, 7, 14, or 21 additional days before storage (16 ± 1C, 85% RH). Midway through storage, roots were heated (32 ± 1C, 85% RH) for 0, 7, 14, or 21 days and placed back into storage. Before being bedded, roots were presprouted (32 ± 1C, 85% RH) for 0, 7, 14, or 21 days. Roots that received extended curing, midstorage heating, or presprouting or a combination of these treatments emerged earlier and produced more cumulative early, midseason, and total plants than nonheated roots. Roots heated once for 21 days produced more plants than roots heated once for 14 days; those heated for 21 days in a combination of short durations produced more early, midseason, and total number of plants than roots heated once for 21 days.