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  • Author or Editor: Carl J. Rosen x
  • Journal of the American Society for Horticultural Science x
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Current techniques used in genetic transformation can result in variation of numerous traits in addition to the transformed trait. Backcrossing to the standard genotype can eliminate this variation, but because of the heterozygous nature of potatoes (Solanum tuberosum L), backcrossing is not effective. Therefore, the chances of obtaining altered performance in transformed potato are high. `Superior' potato plants were recently genetically modified to resist attack and damage by the Colorado potato beetle [Leptinotarsa decemlineata (Say)]. The transformed clone, `NewLeaf Superior' (`NewLeaf'), has been shown in previous field trials to be more vigorous than the standard clone. The objective of this 2-year study was to evaluate the performance of `NewLeaf' relative to that of the standard clone at various fertilizer nitrogen (N) levels. The two clones were randomly assigned as subplots to main plots consisting of four N levels (28, 112, 224, or 336 kg·ha-1). Based on regression analysis, total yield was higher for `NewLeaf' than for `Superior' at N rates below 92 kg·ha-1 in 1997. At higher rates, however, `Superior' had higher yields than the transgenic clone. In 1998, the clon×N rate interaction was significant, but there was no consistent trend to the response of the two clones to N application. At the 112 kg·ha-1 N rate, total yield was higher for `NewLeaf' than for `Superior', but yields were similar for the two clones at other N rates investigated. Nitrogen and biomass accumulation in vines increased more for `NewLeaf' than for `Superior' as N rate was increased from 28 to 336 kg·ha-1. At equivalent N rates, these traits were higher for the transformed than for the standard clone within the range of N rates investigated. However, harvest index at equivalent N rates was higher for the standard clone than for `NewLeaf'. `Superior' and `NewLeaf' produced similar tuber dry weight yields per unit of N supplied and per unit of N absorbed by the plant. Nitrogen uptake efficiency (NUE) was 16% higher for `NewLeaf' than for the standard clone at the low N rate (112 kg·ha-1), whereas at higher N rates NUE was either lower for `NewLeaf' or similar for the two clones. This observation, together with the finding that yield for `NewLeaf' was maximized at lower N levels than the standard clone, suggests that `NewLeaf' may require lower N input than the standard clone. Results from the study indicate that the greater efficiency of `NewLeaf' at lower N levels was associated with acquisition of N from the soil rather than utilization of absorbed N in metabolism.

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Abstract

Nutrient solution experiments were conducted to characterize the absorption of K+ and NH 4 + , as affected by plant K+ status and solution concentrations of K+ and NH 4 + , for tomato (Lycopersicon esculentum Mill. cv. UC823) and ‘French’ prune scions (Prunus domestica L.) on Myrobalan 29C rootstocks (P. cerasifera Ehrh.). Prune and tomato plants pretreated in solutions adjusted daily to 1000 μm K+ had significantly higher K+ concentrations in leaves and roots than those plants pretreated in nutrient solutions adjusted on alternate days to 100 μm K +. NO differences in total N concentrations of roots or leaves due to pretreatment were detected. Potassium uptake rates of prune and tomato plants of high K+ status were significantly lower than those of low K+ status. For both plant species, NH 4 + uptake by roots was independent of plant K+ status. On a relative basis, the presence of solution NH 4 + inhibited K+ uptake to a greater extent in K+-loaded plants than in K + -starved plants. Potassium status of the plant had no effect on the extent of NH 4 + uptake inhibition due to solution K +. Ammonium-induced efflux of K+ from plant roots to initially K+ -free solutions was greater from roots of high K+ status than from roots of low K+ status. Increasing solution NH 4 + concentrations from 100 μm to 1000 μm significantly lowered the K+ uptake rates. The effect was much more dramatic in prune than in tomato. Increasing solution K+ concentrations from 100 μm to 1000 μm had no significant effect on the NH 4 + uptake by either plant species.

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The effects of pH and N form on growth and nutrition of blueberry (Vaccinium corymbosum L. × V. angustifolium Ait. cv. Northblue) and cranberry (V. macrocarpon Ait. cv. Searles) were tested in separate greenhouse hydroponic experiments. A factorial treatment arrangement of two pH levels (4.5 and 6.5) and three N forms (NO3-N, NH4-N, and NH4-N/NO3-N) was used for each clone. Blueberry shoot growth and final dry weight were greatest at pH 4.5, regardless of N form. In contrast, cranberry fresh weight accumulation and final dry weight were higher with NH4-N/NO3-N or NH4-N than with NO3-N alone. Cranberry plants receiving NO3-N alone accumulated low levels of tissue N and grew relatively poorly at both pH levels. Differences in N response by these two species may be due partially to the environments in which they were selected. Soil from the site where `Northblue' blueberry was selected contained relatively high NO3-N and low NH4-N levels; soil from commercial `Searles' cranberry bogs had relatively low NO3-N and high NH4-N levels. Both species accumulated relatively high levels of root Fe, regardless of pH or N form. Levels of Fe in the root were as much as 100 times higher than in the shoot. Based on X-ray microanalysis of cranberry roots, most of the Fe appeared to be precipitated on the root surface as iron phosphate. Concentrations of Mn in shoots and roots depended on N form and pH. In general, root Mn was highest at pH 6.5 and apparently was precipitated with Fe.

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Poinsettia (Euphorbia pulcherrima Wind. ex. Klotzsch cv. Gutbier V-14 Glory) plants were grown under conditions simulating commercial stock plant production to investigate the effects of NH4-N: NO3-N fertilizer ratios, foliar Ca sprays, medium-applied Ca, and medium-applied Mo on leaf edge burn (LEB) and cutting production. Leaf edge burn expression was nearly 100% greater with NH4-N: NO3-N fertilizer ratios of 1:2 or 2:1 than with NO3-N only. However, cutting production was 28% lower with NO3-N as the sole N source. There was little difference in either LEB or cutting production between the two NH4-N levels. Weekly Ca sprays at 500 mg·liter-1 were effective in reducing LEB, while medium-applied Ca as gypsum was ineffective. Foliar Ca sprays reduced both the number of LEB leaves (90%) and symptom severity of individual leaves. Spraying plants with tap water (Ca at 25 to 30 mg·liter-1) plus wetting agent had an intermediate effect. Medium-applied Mo was ineffective in reducing LEB, despite greatly increasing leaf Mo levels. The Ca concentration in chlorotic, marginal leaf tissue was significantly lower than the Ca concentration in green leaf margins. There was also a strong, negative correlation between the Ca concentration in young leaves at the susceptible growth stage and the incidence of LEB in various treatment groups. Supplemental applications of Ca and Mo did not consistently affect cutting production. Leaf edge burn appears to be a localized Ca deficiency due to inadequate Ca uptake and/or translocation to the numerous axillary shoots simultaneously developing on poinsettia stock plants.

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Progenies from crosses among eight highbush (Vaccinium corymbosum L.), lowbush (V. angustifolium Ait.), and V. corymbosum/V. angustifolium hybrid-derivative parents were evaluated in vitro at low (5.0) and high (6.0) pH for vitality, height, and dry weight. Succinic acid and 2[N- morpholino]ethanesulfonic acid (Mes) effectively maintained pH in the medium and rhizosphere. The pH regime did not affect percent radicle emergence from seed or survival; however, percent seed germination was slightly lower at high pH. The parental general combining ability (GCA), reciprocal and maternal, but not the specific combining ability (SCA) variance components were significant for plant vitality, height, and dry weight. The GCA variance components were six to 26 times larger than the SCA variance components for the plant growth traits. Variation due to pH regime was significant for vitality and dry weight but not for plant height. The progenies of parents with high percent lowbush ancestry were taller at both pH levels than those with less such ancestry. Little variation was apparent for higher pH tolerance as measured by dry weight; however, the GCA effects suggested that the progenies of some parents performed better than others at high pH. Vaccinium angustifolium parents differed in the extent to which tolerance to high pH was transmitted. In vitro screening in concert with a traditional breeding program should be effective in improving blueberry tolerance to higher pH.

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Thirty-three seedling progenies from crosses among Vaccinium corymbosum L., V. angustifolium Ait., and V. corymbosum/V. angustifolium hybrid-derivative parents, and `Northblue', `Northsky', and `Northcountry' were grown for 2 years at three soil pH levels at Becker, Minn. Iron sulfate and lime were incorporated to amend the soil to pH levels of 4.0 and 6.5, respectively; the native soil, pH 4.5, was the third pH regime. The plants grew well in the low pH regime, poorly in the high pH regime, and intermediately in the native pH regime. Variation among populations was significant for all traits except vitality 18 months after being planted, and pH treatment affected all traits. The pH regime × population interactions were not significant for any of the plant performance characteristics. Nondestructive subjective and objective measurements were positively and highly correlated with total plant dry weight. Therefore, populations could be effectively evaluated for tolerance to higher pH without destroying the plant. Vaccinium angustifolium was not a general source of tolerance to higher pH, but some populations derived from V. angustifolium were tolerant of high soil pH.

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Seedlings from crosses among Vaccinium corymbosum L., V. angustifolium Ait, and V. corymbosum/V. angustifolium hybrid-derivative parents, and micropropagated `Northblue', `Northsky', and `Northcountry' plants, were grown for 2 years at Becker, Minn., in low (5.0) and high (6.5) soil pH regimes. Nutrient composition expressed as a concentration and total content was determined for P, K, Ca, Mg, Fe, Mn, Zn, Cu, and B in the aboveground portion of the plant. Except for Fe, the pH regime effects on aboveground plant nutrient concentration and total content were much larger than population or population × pH regime interaction effects. Population × pH regime interactions were detected for all nutrients expressed as a concentration, except for P. Generalizations about plant performance and nutrient concentration of the plant could only be made in the context of a given pH regime. At low pH, P and Mn tissue concentrations increased and Ca, Mg, and B concentrations decreased as the percentage of lowbush ancestry increased. At high pH, K, Cu, and B concentrations decreased as the percentage of lowbush ancestry increased. Overall plant performance on the higher pH soils appeared to be positively correlated to aboveground tissue concentrations of Mn, K, and Cu. When expressed as total content, population × pH regime effects were only significant for tissue Mn. Differences in total nutrient content attributed to soil pH were primarily related to differences in plant dry weight.

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