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Fusarium crown and stem rot, caused by Fusarium avenaceum, is a serious disease of lisianthus, Eustoma grandiflorum Raf. (Shinn.). While more than 80 new cultivars of lisianthus have been released for sale in the United States in the past decade, there is a lack of information on their susceptibility to this pathogen. Forty-six cultivars of lisianthus were evaluated for resistance to F. avenaceum. Cultivars were grouped according to blue/purple, pink, or white colors and evaluated within their color class. Although all cultivars evaluated were susceptible to F. avenaceum, partial resistance was observed as indicated by differences in the length of time to symptom expression and in the frequency of diseased plants. `Ventura Deep Blue' and `Hallelujah Purple' (25%) in the blue group, `Bridal Pink' (23%) in the pink group, and `Heidi Pure White' (53%) in the white group had the lowest frequency of diseased plants at 55 days after inoculation. In 21 of the 46 cultivars, 80% to 100% of the plants expressed symptoms at 55 days after inoculation. Screening cultivars for resistance to F. avenaceum is the first step to breeding and developing resistant cultivars. These results also can be useful to growers who could select cultivars that express some level of resistance as an aid in management of this disease until more resistant cultivars are released.

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A GUS marker was used in earlier experiments to show that crown gall resistant Vitis genotypes show significantly lower rates of transformation by A. vitis than the crown gall susceptible Vitis vinifera. In recent experiments a reporter gene (lacZ) fused with the virB promoter was used to determine whether the lower frequency of transformation resulted from reduced induction of Agrobacterium vitis virulence (vir) genes. With some A. vitis strains, addition of medium conditioned with grape tissue enhanced vir induction by the known inducer acetosyringone and significant vir induction also resulted without addition of acetosyringone when grape tissue was included in the induction medium. Enhancement of vir induction by grape extracts was not correlated with genotypic susceptibility to crown gall.

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Abstract

Single applications of ancymidol at 0.03, 0.12, 0.50, or 1.0 mg/plant were soil applied to asparagus seedlings (Asparagus officinalis L.) 3.5, 5.5, or 7.5 weeks after seeding. Increasing ancymidol rates from 0.03 to 1.0 mg/plant decreased bud number, fern dry weight, but not shoot number at all application times. When ancymidol was applied at 1.0 mg/plant at 3.5 weeks it reduced fleshy root production, but in plants treated at 5.5 to 7.5 weeks, it did not reduce fleshy root production. Increasing ancymidol rates from 0.03 to 1.0 mg/plant reduced the crown dry weight of plants 5.5 weeks and younger. Ancymidol from 0.03 to 1.0 mg/plant applied to 3.5-week-old plants increased the partitioning of dry matter into fern rather than crowns, but delaying application to 7.5 weeks after seeding reversed this relationship suggesting increased carbohydrate storage. Application of ancymidol from 0.03 to 1.0 mg/plant to plants 5.5-weeks-old or younger was considered detrimental to plant growth. Ancymidol at 0.50 mg/plant or less applied to 7.5-week-old plants enhanced the production of a stocky, compact transplant. Chemicals used. Ancymidol: α-cycloprophyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol.

Open Access

Since 1924, the Univ. of Minnesota herbaceous perennial breeding program has released n = 84 garden chrysanthemums (Dendranthema grandiflora). Recent breeding objectives have focused on development of non-destructive phenotypic markers and laboratory freezing tests for continued selection of cold-tolerant Dendranthema, Gaura, and other herbaceous perennial flowers. Such methods have become critical to flower breeding programs during periods of above-average winter temperatures and minimal snow cover. Two different laboratory freezing tests were evaluated for their effectiveness in determining cold tolerance. Acclimated crowns of n=6 hardy and non-hardy garden chrysanthemum genotypes were used in Omega Block (detached, emergent rhizomes) and chamber (intact crowns with emergent/non-emergent rhizomes) freezing test methods. Comparative winter survival in the field was monitored over locations and years. Cold tolerance was assessed at 0 °C to -12 °C with varying ramp and soak time periods. LT50 temperatures and number of living emergent rhizomes were determined. Rhizome quality at 1 cm, 3 cm, and 5 cm depths was rated on a 0 (dead) to 5 (undamaged) scale. The chamber freezing method was the most powerful to discern LT50 values. Cold tolerant genotypes included `Duluth' and 98-89-7 (LT50 = -12 °C). Three genotypes had intermediate cold tolerance (LT50 = -10 °C) and one genotype was not cold tolerant (LT50 = -6 °C). Cold-tolerant genotypes also had significantly higher regrowth ratings for rhizomes at 1cm and 3cm depths. Future research will use the chamber freezing method to assay the inheritance of winter hardiness in intact crowns of segregating populations.

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Two experiments were conducted to develop a protocol for rooting stem cuttings from 3-, 5-, and 7-year-old fraser fir [Abies fraseri (Pursh) Poir.] Christmas trees. The first experiment tested the effect of stumping treatments and tree age on shoot production and subsequent adventitious rooting. One auxin concentration [4 mm indole-3-butyric acid (IBA)] and a nonauxin control were tested. Stock plants were stumped to the first whorl (trees in the field 3 and 5 years) or the first, third, and fifth whorls (trees in the field 7 years). Intact (nonstumped) controls were also included for each age. The second experiment was designed to create a quantitative description of the effects that crown (foliage and above ground branches of a tree) position have on the rooting of stem cuttings collected from stumped and nonstumped trees. The exact position was determined by measuring the distance from the stem, height from the ground, and the degrees from north. Crown positions were recorded as cuttings were collected and then cuttings were tested for rooting response. The rooting traits assessed in both experiments included rooting percentage, percent mortality, number of primary roots, total root length, root symmetry, and root angle. In the first experiment, rooting percentage, primary root production, and total root length increased as the age of the stock plant decreased and the severity of the stumping treatment increased. Auxin treatment significantly increased rooting percentage, root production, root lengths, and root symmetry while decreasing mortality. Overall, the highest rooting percentages (51%) and the greatest number of primary roots (8.1) occurred when 3-year-old stock plants were stumped to the first whorl and treated the cuttings with 4 mm IBA. The greatest total root lengths (335 mm) occurred in cuttings from the 3-year-old stock plants. In the second experiment, rooting percentage was significantly affected by the position from which the cuttings were collected. Cuttings collected lower in the crown and closer to the main stem rooted more frequently than cuttings collected from the outer and upper crown.

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Turfgrass growth regulators (TGRs) are an effective means of reducing vertical shoot growth and the production of clippings of tall fescue (Festuca arundinacea Schreb.). Recently, using TGRs has been suggested as a way to acclimate or precondition turfgrass to stress conditions, possibly through total nonstructural carbohydrate (TNC) accumulations and altered TNC partitioning. The TNC may accumulate in response to growth suppression associated with the TGR application. The objective of this study on tall fescue was to determine the effect of a single trinexapac-ethyl (TE) application on tissue weight and on TNC concentration and weight in leaves, crowns, and roots when sampled 6 to 7 weeks following TE application. This sampling time was chosen to coincide with the 28- to 56-day callback schedule that professional lawn care personnel follow when working with tall fescue. In 1995, a high level of turfgrass maintenance was used, consisting of N applications at 49 kg·ha-1 per month and two mowings per week, while in 1996 a moderate level was used, consisting of N applications at 24 kg·ha-1 per month and one mowing per week. Though TE provided reasonable inhibition of clipping growth for a 4-week period during both years, we observed no increase in tissue weight or in TNC concentration or weight in leaves, crowns, and roots when sampled 6 to 7 weeks after treatment. Chemical name used: [4(cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] (trinexapac-ethyl).

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This study set out to test the hypothesis that the development in the capacity for the maximal rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (VCmax) and the maximum regeneration rate of ribulose-1,5-bisphosphate (Jmax) per unit mass is proportional to the growth temperature under which the leaf develops and to investigate whether the capacity for photosynthetic acclimation to temperature varies genetically within a species by testing genotypes that originated from diverse thermal environments. Acer rubrum L. (red maple) genotypes were subjected to short-term and long-term temperature alteration to investigate the photosynthetic response. We minimized the variation of within-crown light gradients by growing trees in open grown field conditions and controlled temperature on a crown section basis. Thus, we singled out the temperature acclimation affects on the photosynthetic temperature optimum. In response to temperature acclimation, the genotype from the northern United States downregulated both VCmax and Jmax and had a 5 and 3 °C lower temperature optimum than the genotype native to the southern United States. The activation energy increased and was higher for Jmax than for VCmax in both genotypes. With respect to respiration, both genotypes downregulated about 0.5 μmol·m-2·s-1. Although respiration was lower, the increased energy of activation in response to growth temperature resulted in a decrease in maximum net photosynthetic rate (Amax) under saturating light and CO2. The results illustrate that the photosynthetic capacity adjusted in response to growth temperature but the temperature optimum was different among genotypes.

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Host nutritional variables were evaluated for their effects on the severity of crown and root rot of tomato caused by Fusarium oxysporum f.sp. radicis-lycopersici. Tomato (Lycopersicon esculentum Mill.) seedlings (cv. Bonnie Best) were grown in a pathogen-infested, soilless rockwool system in the greenhouse and were fertilized with a nutrient solution that was amended with macro- and microelements at various rates. Disease was evaluated after 2 weeks using an index of 0 to 4, and plant fresh weight was measured. Regression analysis indicated that disease severity was significantly increased by ammonium-nitrogen [NH4Cl, (NH4)6Mo7O24, and (NH4)2SO4], NaH2PO4·H2O, Fe-EDDHA, MnSO4, MoO3, and ZnSO4·7H2O. Disease severity was reduced by nitrate-nitrogen [Ca(NO3)2·4H2O] and CuSO4·H2O. Low rates of NH4NO3 (39 to 79 mg·L-1 N) reduced disease, but rates above 100 mg·L-1 N increased it. Disease was not affected by MgSO4·7H2O. In all cases, plant growth was inversely related to disease severity. Mineral fertilizers had no effect on nutrient solution pH. This information sheds new light on environmental factors that influence plant-pathogen interactions, and may be applied to develop a management strategy for Fusarium crown and root rot based on host nutrition.

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Trees of each of five rootstock genotypes (M.7a, M.9, M.26, MM.111, Mark,) were inoculated above and below ground with three strains of Agrobacterium tumefaciens. These were compared to controls that were uninoculated or inoculated with sterile deionized water. All rootstocks tested were quite susceptible to crown gall, but M.9 and Mark were consistantly among the most susceptible genotypes. Percent of inoculated sites forming galls above ground ranged from 43% in M.7a to 77% in M.9 and the mean size of galls that formed ranged from 3.7 mm in M.26 to 7.7 mm in M.9. All rootstocks except M.9 formed galls at a higher percentage of inoculated sites that were below ground. Percent of below ground inoculations forming galls ranged from 67% in MM.111 to 100% in Mark while mean size of galls underground ranged from 4.2 mm in MM.111 to 15.3 mm in M.9. The proportion of inoculated sites forming galls below ground in M.7a was twice as high as in above ground sites For rootstock × strain means, each measure of crown gall susceptibility above ground was significantly correlated with corresponding below ground data at the 0.01 level. to three rootstocks, some trees inoculated with sterile deionized water also produced apparent galls at sites below the soil line (100% in Mark, 60% in M.7a, 22% in M.26) although none of the above ground control inoculations produced galls. Uninoculated controls showed no gall formation.

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Abstract

Rhizoctonia and Pythium crown and root rot of Euphorbia pulcherrima willd ex Kotzch cv. Annette Hegg Dark Red were suppressed in a composted hardwood bark medium amended with sphagnum peat. The suppression equalled that obtained in an aerated steam-treated peat medium drenched with fungicidies. Growth of ‘Annette Hegg Dark Red’ produced in the sphagnum peat-amended bark was improved over plants produced in a sterilized and fungicide drenched soil-peat-perlite medium. Addition of muck to composted hardwood bark negated the desirable growth effects.

Open Access