morphologic and physiologic processes in response to changing light conditions, which may stimulate or repress plant growth. A number of studies showed that UV-A radiation accelerated growth and modified the morphology of plants ( Bernal et al., 2015 ; Tezuka
Soohyun Kang, Yating Zhang, Yuqi Zhang, Jie Zou, Qichang Yang, and Tao Li
Cinta Calvet, Amelia Camprubi, Ana Pérez-Hernández, and Paulo Emilio Lovato
irregularis simultaneously produced, for equal time, in vivo and in vitro, were evaluated in terms of host root colonization potential and plant growth stimulation. Materials and Methods The fungus used, obtained from Citrus aurantium L. ( Camprubi and
Brent Tisserat and Amy Stuff
., 1993 ). Glycerol has also been used as a carbohydrate supplement to stimulate algae tissue culture growth ( Baweja and Sahoo, 2009 ; Kaczyna and Megnet, 1993 ; Lawlor et al., 1989 ; Marián et al., 2000 ; Robaina et al., 1990 ). For example, red
Marc van Iersel
Various growth stimulators have been reported to improve plant growth. Some of these are formulated to improve root growth, which would be particularly beneficial for reestablishing transplants. Three commercially available plant growth stimulators—PGR IV (MicroFlo, Lakeland, Fla.), Roots2 (Lisa Products Corp., Independence, Mo.), and Up-Start (The Solaris Group, San Ramon, Calif.)—were tested to quantify their effect on post-transplant growth of petunia (Petunia × hybrida Hort. Vilm.-Andr.) and impatiens (Impatiens wallerana Hook.f.) seedlings and to assess their value for the greenhouse industry. Seedlings were transplanted from plug flats into larger 5.6-fl oz (166-cm3) containers and treated with 1.1 fl oz (31 mL) of growth stimulator per plant (22 fl oz/ft2). Applications were made immediately after transplant. None of the treatments affected root mass at any time. Up-Start (2 fl oz/gal) increased final shoot dry mass by ≈20% compared to the control plants. The increase in shoot growth by Up-Start most likely is caused by the fertilizer it contains. Up-Start also increased flowering of petunia from 34 to 40 days after transplant. PGR IV (0.5 fl oz/gal) and Roots2 (1.28 fl oz/gal) did not affect dry mass of the plants. PGR IV increased the number of flowers of petunia and impatiens, but this effect occurred well after the plants were marketable. Roots2 caused a small delay in early flowering and an increase in late flowering of petunia but had no effect on flowering of impatiens. Since the effects of the growth stimulators was either due their fertilizer content (Up-Start) or occurred after the plants would have been sold (PGR IV, Roots2), none of the growth stimulators appears to be beneficial for bedding plant producers.
Marianne Andresen and Nina Cedergreen
oligosaccharins, brassinosteroids, jasmonates, salicylates, and polyamines have also been shown to have growth-regulating properties ( Basra, 2000 ). Natural products are also distributed for their growth-regulating effects, mainly as growth stimulators (see for
H.C. Wien, P.L. Minotti, and V.P. Grubinger
Tomato (Lycopersicon esculentum Mill.) plants grown on polyethylene (PE) mulch in New York State frequently have more branches and increased mineral nutrient uptake and yield than plants not mulched. In four field experiments conducted on a silt loam soil, clear PE mulch stimulated root extension shortly after transplanting. One week after transplanting, roots were significantly longer for mulched than for unmulched plants in all four experiments, whereas aboveground dry matter differences did not become significant until 14 days after transplanting in two of four trials. Mulching increased branching, hastened flowering on basal branches, and increased concentration of major nutrients in the aboveground parts. In the field, stimulation of aboveground growth due to mulch might be brought about by warming of the stem by air escaping from the planting hole in the mulch. However, an experiment with black, white, or clear mulch, in which the planting hole was either left uncovered or covered with soil, showed no effect of hole closure on branching even though air temperature near the stem was increased when holes were left uncovered. The results taken together imply that the increased aboveground growth observed with mulching is a consequence of enhanced root growth and nutrient uptake.
Norman Pellett and David Heleba
Gibberellic acid (GA) and benzyladenine (BA) were evaluated for stimulating shoot growth during rooting of softwood cuttings of two species whose propagation causes bud dormancy. Cuttings of Betula papyrifera Marsh. and Forsythia mandschurica Uyeki `Vermont Sun' were treated with 4 levels of GA or 2 levels of BA while rooting in a polyethylene-covered chamber humidified by fog. GA treated Forsythia produced longer shoots, but did not increase the percentage of cuttings producing new shoots (overcoming dormancy). GA treatments of Betula at 1000, 2500, and 5000 ppm resulted in reduced shoot growth and caused death of most cuttings. BA at 1000 ppm in a solution of ethanol, DMSO, and water was detrimental to cuttings.
Elazar Fallik, Douglas D. Archbold, and Thomas R. Hamilton-Kemp
Some plant-derived natural volatile compounds exhibit antifungal properties and may offer a tremendous opportunity to control the causes of postharvest spoilage without affecting fresh produce quality or leaving a residue on the produce. E-2-hexenal has shown significant potential for use as a fumigant for controlling Botrytis cinerea in prior studies. In in vitro studies on the mode of action of E-2-hexenal, mycelial growth and percent spore germination were inversely proportional to concentrations of the compound. Spore germination was found to be more susceptible to the compound then mycelial growth. Much higher concentrations of E-2-hexenal were required to inhibit mycelial growth than spore germination. Lower concentrations of the compound significantly stimulated mycelial growth, especially when the volatile was added 2 days following inoculation. Light microscopy analysis revealed that a high concentration of the volatile damaged fungal cell wall and membranes. Treatment with a high vapor phase level of E-2-hexenal during postharvest storage of strawberry fruit at 2°C prevented botrytis development in a subsequent storage period at 15°C. However, treatment with a low vapor phase level enhanced botrytis development. The implications of these results with respect to the practical use of E-2-hexenal and other natural volatile compounds will be discussed.
Elazar Fallik, Douglas D. Archbold, Thomas R. Hamilton-Kemp, Ann M. Clements, Randy W. Collins, and Margaret M. Barth
Some plant-derived natural volatile compounds exhibit antifungal properties and may offer an opportunity to control the causes of postharvest spoilage without affecting quality of, or leaving a residue on, fresh produce. The natural wound volatile (E)-2-hexenal has exhibited significant antifungal activity in earlier studies, but effects on spore germination and mycelial growth have not been separated, nor has the inhibitory mode of action been determined. To determine the efficacy of (E)-2-hexenal for control of Botrytis cinerea Pers. ex Fr. spore germination and mycelial growth, and to examine the mode of action, in vitro and in vivo studies were performed. Under in vitro bioassay conditions, spore germination was more sensitive to the compound than was mycelial growth. Vapor from 10.3 μmol of (E)-2-hexenal in a 120-mL petri dish completely inhibited spore germination. However, 85.6 μmol of (E)-2-hexenal was required to completely inhibit mycelial growth. Lower concentrations of the compound (5.4 and 10.3 μmol) significantly stimulated mycelial growth, especially when the volatile was added 2 days following inoculation. Mycelial growth did not occur as long as the vapor-phase concentration was 0.48 μmol·L-1 or greater. Light microscopy analysis indicated that a high concentration of volatile compound dehydrated fungal hyphae and disrupted their cell walls and membranes. Exposure of B. cinerea-inoculated and non-inoculated strawberry (Fragaria ×ananassa Duch.) fruit in 1.1-L low-density polyethylene film-wrapped containers to vapor of (E)-2-hexenal at 85.6 or 856 μmol (10 or 100 mL, respectively) per container for durations of 1, 4, or 7 days during 7 days of storage at 2 °C promoted the incidence of B. cinerea during subsequent shelf storage at 20 to 22 °C. Loss of fruit fresh mass and fruit firmness during storage at 22 °C was increased by (E)-2-hexenal treatment, but fruit total soluble solids, pH, titratable acidity, and color (L, C, and H values) were not affected. Thus, maintenance of a high vapor-phasel level of (E)-hexenal, perhaps >0.48 μmol·L-1, may be necessary to inhibit mycelial growth and avoid enhancing postharvest mold problems, while significantly higher levels may be necessary to completely eliminate the pathogen.
Steven F. Vaughn, Mark A. Berhow, and Brent Tisserat
seedmeal ( Vaughn et al., 1996 ). Although 3-MPAN is phytotoxic at higher application rates, it has been found to promote growth at lower rates ( Vaughn et al., 1996 ). Meadowfoam seedmeal contains, on average, 1.5 mg of 3-MPAN/g seedmeal ( Vaughn et al