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  • Author or Editor: F.T. Davies Jr. x
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Abstract

A digital automated irrigation-syringe system (DAIS) that monitors environmental conditions for efficient plant cooling and water usage is described. The device consists of a short-cycle syringe irrigation control (intermittent irrigation) for reducing heat load and a long time cycle control for applying larger volumes of water during predetermined irrigation cycles. The syringe (intermittent irrigation) control is operated by selecting threshold levels based on soil and air temperatures and soil moisture. The longer time cycle control is based on a 24-hr cycle that provides regular cyclic irrigation adjusted for daily irrigation number(s) and time length of each irrigation. The DAIS can be used in nursery container and greenhouse production and can be applied to modeling of growth at different water regimes to determine water requirements for optimum crop growth.

Open Access

Abstract

Crape myrtle (Lagerstroemia indica L. ‘Near East’) explants of 2 nodes were cultured on woody plant medium (WPM) supplemented with PBA, BA, or kinetin. PBA was most effective in promoting axillary shoot proliferation. Maximum number of axillary budbreaks occurred on modified WPM containing 3-9 μm PBA. Subcultured shoots ≥2 cm in length rooted in medium without auxin, and ex vitro rooting and acclimization was also obtained. Chemical names used: 1H-indole-3-butanoic acid (IBA); N-(phenylmethyl)-9-(tetrahydro-2H-pyran-2-yl)-9H-purin-6-amine (PBA), N- (phenylmethyl)-1H-purin-6-amine (BA); N-(2-furanylmethyl)-1H-purin-6-amine (kinetin).

Open Access

Abstract

The design for a chamber to control high root-zone temperature is presented. Air within the insulated chamber was heated with vinyl-jacketed heating cables and cooled with 1:1 water and antifreeze (v/v) pumped through copper coils. Control of the soil temperature was based upon air temperature around the soil containers within the sealed chambers. Chamber operating temperatures could be held between 20° and 50°C ± 0.2° SE.

Open Access

Abstract

Leaf cuttings of Rieger elatior begonias (Begonia bertini ‘compacti’ × B. socotrana cvs. Aphrodite Cherry Red and Schwabenland Red) were treated with 6-furfurylamino purine (kinetin), 6-benzylamino purine (BA), and 6-(benzylamino)-9-(2-tetrahydropyranyl)-9H-purine (PBA). BA and PBA enhanced bud and shoot regeneration in ‘Aphrodite Cherry Red,’ while kinetin showed no activity. All cytokinins tested reduced shoot development in ‘Schwabenland Red.’ PBA stimulated optimal bud and shoot development when applied to ‘Aphrodite Cherry Red’ leaf cuttings as a 12 hour 15 μM basal-petiole dip, 1000 μM spray, and 0.01% talc-petiole- dip. Cuttings taken from ‘Aphrodite Cherry Red’ stock plants treated with 1000 μM PBA successfully generated new plants.

Open Access

Abstract

Adventitious root formation was stimulated with foliar application of indolebutyric acid (IBA) from 1000 to 1500 mg/liter for juvenile and 2000 to 3000 mg/liter for mature leaf bud cuttings of Ficus pumila L. IBA increased cambial activity, root initial formation, and primordia differentiation and elongation. IBA stimulated rooting when applied to juvenile cuttings at 3, 5, or 7 days after experiment initiation, but had no effect on mature cuttings when applied at day 15, the final treatment period. The interaction of IBA/gibberellic acid (GA3) did not affect early root development stages, but reduced root elongation and quality once primorida had differentiated. IBA/6-(benzylamino)-9-(2-tetrahydropyranyl)-9H-purine (PBA) inhibited rooting at early initiation stages.

Open Access

Pinus taeda L. seedlings inoculated with the ectomycorrhizal fungus, Pisolithus tinctorius, were grown in a glasshouse for eight months, and then subjected to rapidly developing cyclic water deficits, or to a single slowly developing water deficit. Water deficits developed at a rate of -0.16 MPa per day (predawn total water potential) for five cyclic water deficits, and at -0.04 MPa per day for the slow water deficit. In unstressed seedlings, carbon exchange rates (CER) did not differ between noninoculated and inoculated seedlings. During slow water deficit development, CER steadily declined. During rapid water deficit development, CER remained unchanged, then declined rapidly when water potentials fell below -1.3 MPa. Inoculated seedlings had higher CER when water potential was lower than -1.5 MPa.

Free access

Pinus taeda L. seedlings inoculated with the ectomycorrhizal fungus, Pisolithus tinctorius, were grown in a glasshouse for eight months, and then subjected to rapidly developing cyclic water deficits, or to a single slowly developing water deficit. Water deficits developed at a rate of -0.16 MPa per day (predawn total water potential) for five cyclic water deficits, and at -0.04 MPa per day for the slow water deficit. In unstressed seedlings, carbon exchange rates (CER) did not differ between noninoculated and inoculated seedlings. During slow water deficit development, CER steadily declined. During rapid water deficit development, CER remained unchanged, then declined rapidly when water potentials fell below -1.3 MPa. Inoculated seedlings had higher CER when water potential was lower than -1.5 MPa.

Free access

Abstract

High root-zone temperatures can stress container-grown plants and ultimately reduce nursery productivity in the southern United States. Water relations of glasshouse-grown Berberis thunbergii DC ‘Atropurpurea’ Buxus microphylla Seibold and Zucc japonica and Pittosporum tobira, (Thunb.) Ait. ‘Wheeler’ were studied under high-temperature root-stress conditions using container-grown plants that were either colonized with vesicular arbuscular mycorrhizal fungi (VAM) or noncolonized. Predawn xylem water potential in stems (ψstem) increased initially (more positive) in response to high root-zone temperatures (40° to 45°C), and then decreased over a 5-day period. Stomatal conductance (gs) and evapotranspiration (ET) were reduced incrementally over time in response to high root-zone temperatures. Root damage occurred, as indicated by reductions in root quality and gs at 35° and 40° for B. thunbergii and P. tobira, and at 40° and 45° for the more high-temperature-resistant B. microphylla. Colonization increased gs and ET of B. microphylla at ambient (25°) and high temperatures (45°) and increased ET of B. thunbergii at 25°. Colonized plants had lower (more negative) ψshoot with initial exposure to increased root-zone temperatures; however, throughout the remainder of the study period there was little reduction in plant stress with the mycorrhizal isolates used. Root hydraulic conductivity (Lp) increased markedly in B. thunbergii compared to B. microphylla at 40° and 45°, indicating less high-temperature resistance in B. thunbergii roots. Mycorrhizal colonization did not moderate hydraulic conductivity at high root-zone temperatures of 40° and 45°. Of the two species, mycorrhizal B. thunbergii had lower Lp at 25° and B. microphylla had lower Lp at 35°.

Open Access

Rooted cuttings of Hibiscus rosa sinensis L. cv. Leprechaun were irrigated with full strength Hoaglands solution containing 0, 2.5, or 10 mM K+. Half of the plants at each K+ level were subjected to a 21-day slowly developing drought stress cycle (DS) followed by a recovery period (day 22), while the other half were non-drought stressed (NDS). Midday leaf water potential (Ψleaf) at day 21 were -1.5 to -1.6 MPa for DS and -0.5 MPa for NDS plants. Photosynthesis (A) was lowest during early stress and recovery of 0 mM K+ plants. Transpiration (E), stomatal conductance (g), and instantaneous water use efficiency (A/E), were generally lowest in 0 mM K+ plants. During peak stress, A was highest in the 2.5 mM K+ plants, whereas E was lowest and A/E highest in 10 mM K+ plants. Ψleaf did not differ among K+ treatments during peak stress and recovery, but osmotic potential was highest (least negative) and turgor potential lowest in 0 mM K+ plants. DS plants had lower carbon isotope discrimination (Δ) compared to NDS plants at all K+ levels, suggesting higher A/E for DS plants. Although there was no significant K+ effect, there was a trend at peak drought stress of Δ lower A and higher A at the 2.5 mM K+ level.

Free access

Growth recovery of mycorrhizal (VAM) and nonmycorrhizal (non-VAM) neem plants after drought exposure were followed under low phosphorus conditions. Drought significantly decreased plant growth regardless of mycorrhiza. Relative growth rate of droughted plants was greater than nondroughted plants during the growth recovery period, and compensated the loss of growth during the previous drought. VAM increased plant growth and improved regeneration of new roots outside the original root balls, particularly in plants previously exposed to drought. New roots of VAM plants were readily colonized by the VAM fungi, while those of non-VAM plants remained uncolonized. VAM growth enhancement after drought exposure was associated with greater uptake of phosphorus and other nutrients, and improved root regeneration.

Free access