Dennis R. Decoteau

Plastic Mulch Color Effects on Reflected Light and Tomato Plant Growth

Abstract Effects of plastic mulch color on upwardly reflected light and on the growth of tomato plants were investigated. Plants grown in sunlight over black polyethylene mulch had fewer axillary shoots (branches) and were taller than plants grown over white polyethylene mulch. The black surface reflected less total light and less blue light, but a higher ratio of far-red (FR) relative to red (R) light. In a controlled environment, tomato plants that were exposed to brief periods of FR at the end of the daily photosynthetic period were taller than those that received brief periods of R. The effect of FR on plant height could be reversed by R and implies phytochrome involvement. Differences in the light spectrum reflected from the plastic, and the similar differential responses to mulch color and light treatments, suggest that tomato plants grown in plastic mulch culture may respond to relatively small changes in light environment induced by the surface color of the mulch.

The influence of plant growth regulators and light on microtuber induction and formation in Dioscorea alata L. cultures

The effects of plant growth regulators, light intensity, and end-of-day (EOD) light quality treatments on node and microtuber induction (% of cultures with microtubers) and development (fresh weight of microtubers) in yam (Dioscorea alata L. cv. Oriental) cultures were investigated. Nodal segments were excised from plantlets cultured on tuberization medium containing growth regulators and exposed to various light treatments. Absciscic acid (1 μM) stimulated and cytokinins (2.5 μM) inhibited microtuber development from yam nodal segments cultured on Mantells and Hugos full-strength tuberization medium under 8-h photoperiods. EOD far-red (FR) light inhibited microtuber induction and development and enhanced node formation. EOD FR light effects were nullified by immediately following the FR treatment with red light. This suggested the involvement of phytochrome in these processes. The lowest light intensity evaluated (12 μmol m−2 s−1) inhibited microtuber, root and shoot production as compared to light intensities of 42, 72 and 102 μmol m−2 s−1. Kinetin (2.5 μm) in half-strength tuberization medium inhibited microtuber induction and development but did not affect node production in the light intensity evaluation.

Picolinic acid-induced direct somatic embryogenesis in sweet potato

Somatic embryos are being considered as an alternative material for in vitro germplasm conservation of sweet potato [(Ipomoea batatas (L.) Lam.)]. Picolinic acid was tested for somatic embryo production in sweet potato apical meristem tip cultures. Low level (0.2 mgl-1) of picolinic acid combined with kinetin or 6-benzylamino purine (6-BAP) (1.0 and 2.0 mgl-1) suppressed shoot growth and induced callus proliferation. Increased amount of picolinic acid (2 and 3 mgl-1) in combination with kinetin (0.25 and 1.0 mgl-1) induced direct somatic embryogenesis from apical meristem tips of variety Regal but not in Jewel. The primary embryos matured and germinated bipolarly yielding whole plantlets and unipolarly producing embryogenic hyperhydrated-fasciated shoots. The hyperhydrated-fasciated shoots, when cultured in picolinic and kinetin-enriched medium, produced secondary embryos. The secondary embryos also germinated bipolarly and unipolarly, resulting in subsequent cycles of embryogenesis. This recurrent embryogenesis ensures maintenance and proliferation of embryogenic tissues. Somatic embryos were also formed in mannitol-induced hyperhydrated shoots in response to picolinic acid and kinetin or 6-BAP treatment. Embryogenesis did not occur in non-hyperhydrated leaf, petiole, and internode sections.

Heat units to predict tomato harvest in the southeast USA

Abstract Planting and first harvest dates of tomato ( Lycopersicon esculentum Mill.) from 2 seasons in 3 years at eight locations in Georgia, North Carolina and South Carolina formed 38 environments which were used to determine the most reliable method to predict fast harvest date of tomato based on daily maximum and minimum air temperature. Eleven methods of calculating heat units were chosen for comparison based on their performance as described in the literature. The most reliable method was defined as the one with the smallest coefficient of variation (CV). CVs were calculated for each method over both seasons and locations, for each season over all locations, each location over all seasons, and for each season at each location. All heat unit summation methods had smaller coefficients of variation (CV) than the standard method of counting days from planting to first harvest. Heat unit summation methods improved harvest date prediction accuracy compared with the counting day method for tomatoes in the South Atlantic Coast (SAC) region. Prediction using location/season specific models were less variable than the models over all seasons and locations. Incorporating daylength improved model prediction accuracy when applied over all locations and seasons, all locations by season, and all seasons by location. Based on the results of this study, the heat unit summation technique recommended for this region (where the location and season specific models are not available) is the reduced ceiling method multiplied by daylength.

Young watermelon plant growth responses to end-of-day red and far-red light are affected by direction of exposure and plant part exposed☆

Differences in the growth regulating ability of end-of-day (EOD) red (R) and far-red light (FR) as affected by direction of exposure (predominantly downwardly versus upwardly directed) and plant part exposed (adaxial and abaxial surface of leaf 1, and junction and opposite the junction of the attachment of the petiole to the stem) were determined on young watermelon (Citrullus lanatus (Thumb.) Matsum and Naki cv. Sugar Baby) seedlings in a controlled environment. Whole-plant exposure to downwardly or upwardly directed EOD FR stimulated elongation of internode 1 and the petiole of leaf 1 (as measured from the cotyledons) as compared to control seedlings (no EOD light). Upwardly directed EOD FR also induced elongation of internode 2, stem length, and leaf petioles 2 and 3 as compared to controls. This EOD FR induced elongation was reversed by following the FR with a red light treatment (FR + R) implicating phytochrome regulation. Upwardly directed EOD FR increased the leaf angle of leaf 1 as compared to controls. Upwardly directed EOD R and EOD FR + R increased the petiole angle of leaf 1. Irradiation of the adaxial surface of leaf 1 with fibre-optic transmitted EOD FR (tissue area exposed approximately equal to 20cm*) enhanced elongation of internode 1 by 88% as compared to controls. Irradiation of the abaxial surface of leaf 1 and the junction and side opposite the junction of the point of attachment of petiole 1 to the stem with EOD light had no effect on elongation of internodes 1 and 2 or stem length. In conclusion, the growth regulating ability of photomorphogenic light (as provided by EOD R and FR) was affected by predominant direction of exposure

Changes in soluble carbohydrates during phytochrome-regulated petiole elongation in watermelon seedlings

Changes in soluble carbohydrate composition and concentration in leavesand petioles of watermelon (Citrullus lanatus (Thunb)Matsum and Nakai cv. Sugar Baby) seedlings during early stages ofphytochrome-regulated petiole elongation were investigated. Watermelon seedlingswere grown in a controlled environment with 350 μmolm−2 s−1 photosynthetically activeradiation (PAR) during a 12-h photoperiod. Low intensity end-of-day(EOD) light treatments (for 15 min) of red (R), far-red (FR) and FRfollowed by R (FR/R) were initiated when the seedlings were 14 days old.Seedling growth, and soluble carbohydrate concentration and composition inleaves and petioles were determined after 3 and 6 days of EOD light treatments.The EOD FR increased the petiole length and dry mass partitioned to petioles asearly as 3 days into the treatment. This increased petiole dry mass inFR-treated plants was accompanied with an increase in reducing sugar (glucoseand fructose) concentration in the petioles. Although both leaves and petiolesshowed this effect, the relative increase was greater in petioles than leaves.While the most abundant sugars in petioles were fructose and glucose, thepredominant sugars in leaves were sucrose, raffinose, and stachyose. Thephotoreversion of FR induced changes in growth and sugar concentrations by Rindicates the involvement of phytochrome in these processes.

Determination of Optimum Levels of Light Irradiation Needed to Control Ripening of Tomatoes

Optimum levels of lighting parameters (light quality, irradiation time, and irradiance) and variety effect on inducing or delaying tomato ripening were identified by evaluations of specific physical and chemical characteristics using factorial designs. Under red light (R) or red plus blue light (R+B) irradiation, an irradiation time of 3 to 5 min at any level of irradiance tested was effective in accelerating red and yellow color development in tomatoes. With an irradiance of 38.90 W/m2 under irradiation times of 3 to 5 min, far-red light (FR) was effective in delaying red and yellow color development. No combinations of treatments except variety had a significant effect on firmness. Light treatment effects on soluble solids content, pH, and titratable acidity were not consistent, but tomato variety had a significant influence on measured values of these properties.

Heat units, solar radiation and daylength as pepper harvest predictors

Abstract Daily maximum and minimum air temperature, total solar radiation and daylength data from seven locations during three seasons of 3 years were used to compare 52 heat unit accumulation models with counting days as a harvest prediction method for pepper. The best model was defined as the one with the least variation, i.e. smallest coefficient of variation (CV). CVs were calculated for each method over all seasons and locations, for each method over all locations for each season, and for each method in each season at each location. In all cases heat unit accumulation methods were better than counting days. The location and season specific model was the most accurate, but the analysis over all seasons and locations did result in smaller CVs than counting days, so improved harvest prediction can be achieved by using regionally developed models.

Variation in Ozone Sensitivity Within Indian Hemp and Common Milkweed Selections from the Midwest

Abstract Sixteen selections of Apocynum cannabinum (Indian Hemp) and nine of Asclepias syriaca (Common Milkweed) from midwestern USA were exposed to 40 or 80 ppb ozone under controlled conditions within greenhouse continuously stirred tank reactor (CSTR) chambers to evaluate their relative ozone sensitivity. The incidence and severity of ozone-induced symptoms on both species were directly related to ozone concentration and duration of exposure. The most common foliar symptom was classic, dark, adaxial stipple, similar to symptoms ascribed to ambient ozone in the field. Indian Hemp was more sensitive to ozone than Common Milkweed. Both species exhibited considerable intraspecific variation in ozone sensitivity. Variability in the data was too great to assign definitive ozone-sensitivity ratings within geographic regions from which seed was selected. However, two locations were identified as possible collection sites for ozone-sensitive selections of both species: Wabaunsee County, KS and Plattsmouth, NE for Indian Hemp; and Cloud County, KS and Swan Creek Lake Wildlife Area, NE for Common Milkweed. Plants derived from seed from these locations may serve as ozone-sensitive bioindicators.

Failure of ozone susceptibility tests to predict yield reductions in wheat

Abstract Several measures of injury to wheat seedlings following an acute exposure to ozone were evaluated to determine their effectiveness in predicting susceptible and tolerant cultivars of wheat, Triticum aestivum L., to ozone. Estimates of plant susceptibility from visual injury, chlorophyll loss, and stress ethylene production did not correlate with each other or with actual yield reductions in plants exposed to long term treatment with ozone. The inability of tested measures to accurately predict ozone susceptible and tolerant cultivars limits the use of these measures as rapid screening techniques for determining sensitibity of wheat cultivars to ozone.