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Abstract
Twelve cultivars of sweet potato (Ipomoea batatas (L.) Lam) evaluated for resistance to Meloidogyne incognita (Chitwood) and M. javanica (Chitwood) using “greenhouse bed, ” “greenhouse cylinder, ” and “field” methods. Comparable results were obtained irrespective of the method used; however, the cylinder methods confined roots to an area readily accessible to the nematodes, permitted periodic root observations without destroying the root system, and was more conducive to effective evaluations at an earlier stage.
A study was initiated in an environmental growth room to examine the effects of container size on the growth of several sweetpotato genotypes grown under a nutrient replenishment protocol. Plants were grown from vine cuttings of 15 cm in length, planted in 0.15 × 0.15 × 1.2-m growth channels using a closed nutrient film technique system. Nutrient was supplied in a modified half-strength Hoagland's solution with a 1 N: 2.4 K ratio. Nutrient replenishment protocol consisted of daily water replenishment to a constant volume of 38.4 liters in the small reservoir and 345.6 liters in the large reservoir. Nutrients were replenished as needed when the EC of the nutrient solution fell below 1200 mhos/cm. The design used was a split-plot with the main plot being container size and genotypes the subplot. Nine genotypes were evaluated: J6/62, J6176, J8/1, PX/6, PX/10, PX/36, TU-82-155, TU-J1, NCC58. Results showed no effect of container size on storage root yield, foliage fresh and dry mass, leaf area, or vine length. However, plants grown in the large container accumulated more storage root dry mass than those in the small container. All genotypes evaluated showed variation in their responses for all parameters measured.
The effects of within-channel spacings (WCS; 13, 18, 25 cm) and between-channel spacings (BCS; 13, 25,38 cm) on yield and linear growth rate of sweetpotatoes [Ipomoea batalas (L.) Lam.] grown by use of the nutrient film technique (NFT) were evaluated. Storage root count, fresh and dry weights, and linear growth rate, expressed as root area, declined linearly in response to decreased BCS, while fresh and dry foliage weight decreased linearly and quadratically as spacing was reduced within the growth channels. Neither linear growth rate on a canopy area basis nor the edible biomass index was significantly affected by WCS or BCS.
Growth chamber experiments were conducted to study the physiological and growth response of sweetpotato [Ipomoea batatas (L.) Lam.] to either 50% or 85 % relative humidity (RH). Vine cuttings of T1-155 were grown using the nutrient film technique in a randomized complete-block design with two replications. Temperature regimes of 28/22C were maintained during the light/dark periods with irradiance at canopy level of 600 μmol·m-2·s-1 and a 14/10-hour photoperiod. High RH (85%) increased the number of storage roots per plant and significantly increased storage root fresh and dry weight, but produced lower foliage fresh and dry weight than plants grown at 50% RH. Edible biomass index and linear growth rate (in grams per square meter per day) were significantly higher for plants grown at 85 % than at 50% RH. Leaf photosynthesis and stomatal conductance were higher for plants at 85 % than at 50% RH. Thus, the principal effect of high RH on sweetpotato growth was the production of higher storage root yield, edible biomass, growth rate, and increased photosynthetic and stomatal activity.
A three year study involving solar heating of soil (soil solarization) with clear polyethylene mulch demonstrated for two years, control of root-knot nematodes (Meloidogyne incognita). The population of M. incognita was reduced >90% in the 0-30cm depth of solarized soil. The number of eggs per gram root recovered and the root gall index from `Georgia-Jet' sweetpotatoes were reduced (92-98%) by soil solarization. Growth and yield were enhanced in solarized soil. The beneficial effects of solarization was observed in the second year following two additional cropping cycles of collard greens and sweetpotatoes.
Growth chamber experiments were conducted to study the physiological and growth response of peanut (Arachis hypogaea L.) to 50% and 85% relative humidity (RH). The objective was to determine the effects of RH on pod and seed yield, harvest index, and flowering of peanut grown by the nutrient film technique (NFT). `Georgia Red' peanut plants (14 days old) were planted into growth channels (0.15 × 0.15 × 1.2 m). Plants were spaced 25 cm apart with 15 cm between channels. A modified half-Hoagland solution with an additional 2 mm Ca was used. Solution pH was maintained between 6.4 and 6.7, and electrical conductivity (EC) ranged between 1100 and 1200 μS·cm–1. Temperature regimes of 28/22 °C were maintained during the light/dark periods (12 hours each) with photosynthetic photon flux (PPF) at canopy level of 500 μmol·m–2·s–1. Foliage and pod fresh and dry weights, total seed yield, harvest index (HI), and seed maturity were greater at high than at low RH. Plants grown at 85% RH had greater total and individual leaflet area and stomatal conductance, flowered 3 days earlier and had a greater number of flowers reaching anthesis. Gynophores grew more rapidly at 85% than at 50% RH.
Growth chamber studies were conducted to determine if inverse day/night temperature could control canopy height of sweetpotato without adversely affecting storage root yield. Four 15-cm-long vine cuttings of TU-82-155 sweetpotato were grown in rectangular nutrient film technique hydroponic troughs for 120 days. Two troughs were placed into each of six reach-in growth chambers and subjected to 24/18, 26/20, 28/22, 18/24, 20/26, and 22/28 °C, respectively. Growth chamber conditions included a 12/12-h photoperiod, 70% RH, and photosynthetic photon flux of 1000 μmol·m-2·s-1 at canopy level. Total and edible storage root yields were reduced by 50% among plants grown under cool days/warm nights regimes. Harvest index was similar among treatments except for the low value obtained at 22/28 °C. Canopy height was positively correlated with the change in temperature, and for every 2 °C decrease there was a 3.1 centimeter decrease in canopy height. Inverse day/night temperature effectively controlled canopy height but at the expense of storage root production.
`Georgia Red' peanut (Arachis hypogaea L.) was grown hydroponically at 20/16 °C, 24/20 °C, 28/24 °C, and 32/28 °C, day/night air temperatures to evaluate effects on pod and seed yield, flowering, harvest index, and oil content. Ten-day-old peanut seedlings were transplanted into rectangular nutrient film technique troughs (0.15 × 0.15 × 1.2 m) and grown for 110 days. Growth chamber conditions were as follows: photosynthetic photon flux (PPF) mean of 436 μmol·m-2·s-1, 12 h light/12 h dark cycle, and 70% ± 5% relative humidity. The nutrient solution used was a modified half-Hoagland with pH and electrical conductivity maintained between 6.5 to 6.7, and 1000 to 1300 μS·cm-1, respectively, and was replenished weekly. Vegetative growth (foliage, stem growth, total leaf area, and leaf number) was substantially greater at increasingly warmer temperatures. Reproductive growth was significantly influenced by temperature. Flowering was extremely sensitive to temperature as the process was delayed or severely restricted at 20/16 °C. The number of gynophores decreased with temperature and was virtually nonexistent at the lowest temperature. Pod yield increased with temperatures up to 28/24 °C but declined by 15% at the highest temperature (32/28 °C). Seed yield, maturity, and harvest index were highest at 28/24 °C. Oil content (percent crude fat) increased an average of 23% and was highest at the warmest temperature (32/28 °C). These results clearly suggest that vegetative and reproductive growth, as well as oil content of peanut in controlled environments, are best at warmer temperatures of 28/24 °C to 32/28 °C than at cooler temperatures of 20/16 °C to 24/20 °C.
Two sweetpotato [Ipomoea batatas (L.) Lam] genotypes (`Georgia Jet' and the breeding clone TI-155) were grown at 12-, 15-, 18-, and 21-h light/12-, 9-, 6-, 3-h dark cycles, respectively, to evaluate their growth and elemental concentration responses to duration and amount of daily lighting. Vine cuttings (15 cm long) of both genotypes were grown in rectangular nutrient film technique channels for 120 days. Conditions were as follows: photosynthetic photon flux (PPF) mean 427 μmol·m–2·s–1, 28C day/22C night air cycle, and 70% ± 5% relative humidity. The nutrient solution used was a modified half-strength Hoagland's solution. Storage root count per plant and per unit area, yield (in grams per square meters per day), and harvest index increased, while production efficiency (in grams per mole) decreased with increased daily PPF. Stomatal conductance for both genotypes declined with increased daily PPF. Leaves were smallest for both genotypes at the 21-h light period, while storage root yield declined as leaf area index increased. Except for a linear decrease in leaf N and K with increased light period, elemental concentration was not significantly influenced.
The effects of sequential foliage topping on two sweetpotato [Ipomoea batatas (L) Lam cvs Georgia Jet, TU-82-18921 cultivars were investigated in a field trial. Three initial foliage cuttings (15 cm cutting from the growing tip) were initialed at 45.60 and 75 days after planting (DAP). Each initial cutting date was followed by zero, one or two cuttings at biweekly intervals.
Total storage root yields were not affected by cutting treatments regardless of the cultivar investigated. Both cultivars differed in their response in dry matter accumulation, while Georgia Jet was not affected by cutting treatments, TU-82-1892 accumulated less dry matter when foliage tips were removed twice during the growth cycle (75.90 DAP) compared to all other cutting treatments.
The amount of foliage tips removed from each cultivar differed significantly over all treatment levels with Georgia Jet producing more foliage tips than TU-82-1892. However. production of foliage tips for both cultivars was greatest when foliage cutting was delayed until 75 DAP.