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- Author or Editor: Fred T. Davies Jr. x
This paper describes a laboratory exercise for overcoming dormancy requirements of seeds of ‘Nemaguard’ peach [Prunus domestica (L.) Batsch] through selected mechanical, chemical, and environmental treatments.
Growth and nutrient content of neem tree seedlings (Azadirachta indica A. Juss) were studied in response to the mycorrhial fungi Glomus intraradices Schenck & Smith and Long Ashton Nutrient Solution (LANS) modified to supply phosphorus (P) at 0.65 and 1.30 mM P. Three months after inoculation, an extensive mycorrhizal colonization was observed in mycorrhizal plants at both P levels. Shoot growth of mycorrhizal plants was similar at both P levels while the growth of nonmycorrhizal plants increased with increasing P supply. Mycorrhizal plants had greater leaf area, shoot dry weight and root to shoot ratio than nonmycorrhizal plants at the same P level. The length of nonsuberized roots increased with increasing P supply regardless of mycorrhizal colonization while the length of suberized roots was significantly increased by mycorrhiza. Mycorrhiza altered dry mass partitioning to root systems resulting in greater length and dry weight of suberized roots in mycorrhizal plants. Mycorrhiza also improved nitrogen, phosphorus, calcium and sulfur uptake but did not affect micronutrient uptake, except for enhancing boron.
Micropropagated cactus pear plantlets (Opuntia amyclaea Tenore) cv. Reyna were colonized with a Mexican endomycorrhiza isolate, ZAC-19 (containing Glomus etunicatum and two unknown Glomus spp.) and fertilized with two phosphorous levels (0 and 11 μg P/ml) to study their effect on plant growth and nutrient uptake. After 7 months of greenhouse culture, there was 100% survival of the micropropagated cactus pear plants. Evidence of mycorrhizal colonization was observed 5 days after inoculation, with the development of internal hyphae in root cortices. At the end of the study, high colonization occurred (48% to 54%) with no differences in P treatments. Plantlets transferred to soil began to actively grow with no lag phase. However, plant growth rate was significantly affected by treatments. Absence of P supply and lack of colonization resulted in lower dry mass and surface area of prickly pear cactus plants. In contrast, the combination of supplementary P and mycorrhizal colonization significantly increased plant growth.
Plant propagation instructors are challenged to develop laboratory exercises that demonstrate the theoretical aspects of seed germination. Seed priming or osmoconditioning is a relatively new technigue that has been shown to improve seed performance in horticultural crops. An esaily constructed seed priming system was designed using a pair of 2-liter glass jars, 2 aquarium pumps and air tubing. Eight sets of 40 seeds were each wrapped in coffee filters and laced in aerated treatment solutions consisting of 50 mmole K H2P O4 or an untreated control of distilled water. All seeds were treated or 0, 1, 3 or 5 days. Upon completion, seeds were rinsed, dried and placed into petri dishes containing moist filter paper to observe germination. A good test species for this exercise is Vinca rosea which typically has a poor germination percentage and rate. Seeds primed for 3 and 5 days significantly enhanced both germination percentage and rate in Vinca.
Seedlings of Sophora secundiflora (Ortega) Lag. were grown in 10.2-cm diameter pots containing sterilized media individually inoculated with 1 of 4 vesicular-arbuscular (VA) mycorrhizal fungi and fertilized with Omocote (18N-6P-12K) at rates of 0, 1.2, or 4.2 kg/m3. After 263 days, seedlings inoculated with Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe and with Gigaspora margarita Becker and Hall exhibited increased fresh and dry weights of shoots and roots and root quality at the 1.2 kg/m3 fertilizer level. Increased growth responses of seedlings inoculated with either G. mosseae or G. margarita at 1.2 kg/m3 Osmocote were comparable to noninoculated controls at 4.2 kg/m3. G. etunicatus Becker & Gerd. and G. fasciculatus (Thaxt. sensu Gerd.) Gerd. & Trappe did not enhance seedling growth at any fertilizer rate tested, nor were they colonized on seedling roots. Microscopic examination of roots confirmed VA mycorrhizal colonization at all 3 fertilizer levels with G. mosseae, and at the 2 lowest levels with G. margarita. Increased P uptake occurred only with G. mosseae-inoculated seedlings at 0 and 1.2 kg/m3 fertilization rates.
Single node stem sections of Quercus shumardii Buckl. seedlings were used to propagate Shumard oak in vitro. Stem sections in liquid woody plant medium (WPM) with 8.9 μm (2 mg liter−1) BA produced the greatest number of shoots ≥10 mm. The cytokinin 2iP did not promote axillary shoot growth. Shoots were rooted with 73% success under ex vitro conditions in Jiffy-7 peat pellets after a basal dip in 2.5 μm (0.5 g-liter−1) IBA. Plantlets were acclimatized successfully to greenhouse conditions. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA), N-(3-methyl-2-butenyl)-1H-purin-6-amine (2iP), 1H-indole-3-butanoic acid (IBA), (1α,2β,4aα,4bβ,10β)-2,4a,7-trihy- droxy-1-methyl-8-methylenegibb-3-ene-1,10-dicarboxylic acid 1,4a-lactone (GA3).
The leaves of vegetative stolons of greenhouse grown Cryptanthus `Marian Oppenheimer' (wide leaf clone) were cultured in modified MS media to induce adventitious shoot formation via callus formation. The best callus induction medium was basal MS medium with 10 μM NAA, IBA and BA. Pure green (843), maroon (3), striped (2) and albino plantlets were obtained. Most of the albino plantlets were stunted, tightly clumped together and impossible to score. The medium which produced the highest average number of non-albino plantlets was basal MS medium with 0.3 μM NAA, IBA and BA All non-albino plantlets were rooted in MS medium with 5.4 μM NAA and transplanted ex vitro with a survival rate of 96.7%. The maroon plantlets became green two weeks after transplanting. Histological studies revealed that C. `Marian Oppenheimer' (wide leaf clone) has two tunicas (L1 and L2) and a corpus (L3). Callus on the leaf explant arose mainly from the L2 and L3. Apparently C. `Marian Oppenheimer' (wide leaf clone) is a GWG periclinal chimera.
Variation in tissue elemental concentration in apical stem cuttings of `Lilo' and `V-10 Amy' poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) were studied during the initiation and development of adventitious roots. Changes in selected macro- and micro-element concentrations coincided with root initiation (i.e., Fe, Cu, and Mo accumulated in the basal portions of stem cuttings during early root initiation before root primordia elongation); P, K, Ca, and Mg concentrations declined. During root primordia elongation and root emergence, Fe, Cu, and Mo and Mg, Mn, B, and Zn concentrations continued to increase at the cutting bases, but P and K concentrations remained low compared to when cuttings were initially inserted in the propagation medium. When all cutting of both cultivars had rooted, foliar N, Fe, and Mo concentrations declined, but Cu increased compared to when cuttings were initially propagated.
To determine the role of endomycorrhizae on water relations and plant growth of geraniums under nonrate-limiting soil P conditions, hybrid seedlings (Pelargonium X hortorum Bailey cv. Cherry Glow) were planted in moderately high P (40 ppm) media, grown under high (−0.4 MPa) or low (−1 MPa) soil water potential (ψs), and either inoculated with VA mycorrhizal fungi [Glomus mosseae (Nicol. & Gerd.) and G. fasciculatus (Thaxt. sensu Gerd.) Gerd. & Trappe] (VAM) or left as noninoculated controls. Geraniums grown under high moisture had greater shoot growth, more advanced floral development, and higher P uptake than the low moisture plants. Mycorrhizal plants under high moisture conditions had higher P levels than noninoculated plants, while mycorrhizal plants under low moisture regimes had greater shoot growth, more advanced floral formation, and greater N uptake than noninoculated plants. Xylem water potential in leaves (ψL) was lower under −1 MPa than −0.4 MPa ψS moisture regimes and lowest in mycorrhizal geraniums grown under −1 MPa ψS. One hundred minutes after plants had recovered from water stress, the greatest change in ψL was recorded for mycorrhizal geraniums acclimatized to low moisture regimes. Geraniums under low moisture regimes are more mycorrhizal-dependent. Total estimated root length and root water conductivity were lower with mycorrhizal geraniums under high water and P regime. Under water stress, the larger mycorrhizal geraniums have greater total water demands than controls. Consequently, mycorrhizal geraniums stressed more rapidly yet more efficiently recovered from water deficits. Data suggests that VAM plants acclimate more efficiently to water stress because of more frequent or extreme drought.
A laboratory exercise is outlined and discussed for seed priming, or osmoconditioning. The exercise was developed using an easily constructed and inexpensive seed-priming system. A variety of horticultural seeds can be used to give students experience and exposure to some of the benefits of seed priming. Seed germination data usually can be obtained within 6 to 8 days, depending on the species used. The laboratory may be modified to stress various features of seed priming, including priming agents, optimal concentrations, and ranges of germination temperatures.