Subsequent Root Growth Research Articles

Effects of Supplementary Lighting on Rooting of Rhododendrons

Abstract Supplementary night lighting (2000 HR to 0400 HR) from low-irradiance incandescent lamps (INC) stimulated rooting in Rhododendron ‘Unique’ and increased root-ball diameter of ‘Unique’ and ‘Anna Rose Whitney’ in both spring (Feb.–June) and fall (Sept.–Jan.) propagation. Increasing irradiance during the day with supplementary high-pressure sodium lamps (HPS) during fall propagation inhibited initial root development of ‘Unique’ but stimulated subsequent root growth of both ‘Unique’ and ‘Anna Rose Whitney’. In spring, HPS stimulated root growth in ‘Unique’ but had little effect on ‘Anna Rose Whitney’. Increased irradiance from HPS does not appear necessary for rooting rhododendrons under greenhouse conditions and may be detrimental in the early stages of propagation, especially when natural radiation levels are high.

THE INTERACTION BETWEEN AUXIN AND BORON IN ADVENTITIOUS ROOT DEVELOPMENT

SummaryAn interaction between auxin and boron in the rooting response of stern cuttings of Phaseolus aureus Roxb. is described. The optimum response to one variable is dependent upon the value of the other and vice versa. Whereas the number of roots per cutting which develop is diminished when high concentrations of boron are supplied immediately after treatment of cuttings with auxin, subsequent root growth is enhanced by such treatment. These results are discussed with respect to the possible role of boron in controlling endogenous auxin concentration via an effect on IAA oxidase.

Physical conditions of propagation media and their influence on the rooting of cuttings

The formation and subsequent growth of roots by cuttings of poinsettia, hydrangea, rose and azalea in various propagation media, Jiffy-7, Jiffy-9 and Grodan under different conditions of aeration was investigated. The interrelationships of the effects of air content of the media, temperature and light intensity on the rooting of poinsettia cuttings was also studied. With low air contents (0 cm moisture tension) in the propagation media the formation and growth of roots was strongly inhibited. The rooting performance of rose appeared to be less affected by the poor aeration. Increasing air content improved rooting but best results were obtained at moisture tensions of 4 to 8 cm. Rooting seems to be better correlated with oxygen diffusion rate (ODR) than with air content. For poinsettia cuttings the optimum temperature for rooting was 24 to 28°C. At low temperatures rooting was delayed while at higher temperatures it was almost completely inhibited. Callus formation increased with temperature but decreased with increasing moisture tension. Conditions which induced large callus formation inhibited root formation. High light intensity during rooting reduced overall rooting performance and the inhibition was most pronounced in conjunction with high moisture tensions.

Propagation ofVitis ChampiniPlanchon CV. Ramsey: Relationship between Carbohydrate Metabolism during Storage and Cutting Performance

Propagation of hardwood cuttings of <i>Vitis</i> spp. is known to be influenced by storage practice. In a preliminary investigation of response to storage we have related the effect of no storage, cold storage, and storage in sand at ambient temperatures on carbohydrate metabolism and found that subsequent propagation depended strongly on the extent of allocation of carbohydrate reserves to the soluble fraction. A high content of soluble carbohydrate in the internodes was associated with a low proportion of successfully propagated cuttings. Content of soluble carbohydrates was negatively correlated with starch content, but neither starch content <i>per se</i> nor total content of carbohydrates were statistically associated with proportion of cuttings to propagate or with extent of subsequent growth of shoots and roots.

PRETREATMENT EFFECTS OF CADMIUM ON THE ROOT GROWTH OF HOLCUS LANATUS L.

SummaryA cadmium tolerant and a non‐tolerant population of Holcus lanatus were subjected to a pretreatment with either no or low (0·2 μg Cd ml−1) concentrations of cadmium prior to normal tolerance testing in 1·0 μg Cd ml−1 solution. When pretreated roots were not removed prior to the tolerance test, the cadmium pretreatment resulted in significantly greater root growth of both populations in the test solution relative to plants given no cadmium pretreatment. Repeating the tolerance test on plants which had had their pretreated roots excised prior to testing showed no significant effect of any pretreatment on subsequent root growth in either population. There was an overall difference between the two populations in terms of their response to pretreatment and test concentrations in that when exposed to cadmium, plants of the tolerant population grew significantly better than those of the non‐tolerant population. The data presented provide evidence for a stimulation of cadmium tolerance following low‐level exposure of roots to cadmium. The mechanisms associated with these effects are not clear although cadmium tolerance in animals is known to show similar trends.

Rooting Capacity of Herbicide-Treated Woody Ornamental Plants

The impact of annual preemergence herbicide usage on the rooting potential of seven commercially important woody ornamental species was studied. Granular formulations of dichlobenil (2,6-dichlorobenzonitrile), diphenamid (N,N-dimethyl-2,2-diphenylacetamide), simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine] employed as dormant season or spring applications had no inhibitory effects on the rooting of plants following transplantation. Season of transplanting influenced subsequent root growth of Japanese holly (Ilex crenataThunb. var.convexaMakimo), Rosebud azalea (RhododendronX ‘Rosebud’), and Hicks' yew (Taxus mediaRehd. var.hicksiiRehd.) more than herbicide treatment. Hardwood cuttings taken from plants grown in herbicide-treated soil rooted as well as those from untreated controls. Plants grown in full sunlight or 55% shade exhibited similar root growth and insensitivity to preemergence herbicides.

Respiratory Transition during Seed Germination

Experiments with germinating seeds of Wayne soybean (Glycine max Merr.) show that between the 4th and the 8th hour of germination, respiration experiences a transition from predominantly "alternate" respiration, which is sensitive to salicylhydroxamic acid, to a cyanide-sensitive respiration. The dependence of early germination stages on alternate respiration is reflected in several types of seed functions, including subsequent root growth rate, chlorophyll synthesis, and germination itself. The early period of germination is shown to require a normal O(2) tension, which is no longer a requirement at later stages. The changing sensitivity to cyanide and to salicylhydroxamic acid is found to be common to seven different types of germinating seeds. It is proposed that the alternate pathway of respiration provides something essential for the completion of the earliest stages of seed germination.

Relationships Between the Development of Adventitious Roots and the Biosynthesis of Anthocyanins in First Internodes of Sorghum

The initiation and subsequent growth of adventitious roots in excised first internodes of Sorghum vulgare var. Wheatland milo were studied to determine the effect of these processes on anthocyanin biosyntheses. Segmentation of the internodes inhibited both adventitious root growth and accumulation of cyanidin equally in all segments; these results can be interpreted as a common requirement for bidirectional longitudinal transport. The presence of the coleoptile, especially in the absence of the base of the internode, inhibited the growth of the roots, but increased the number of root initials. High intensities of white and blue light which induced cyanidin synthesis slightly decreased adventitious root growth. Anaerobic conditions produced by solution infiltration strongly inhibited the growth of adventitious roots and greatly increased the accumulation of apigeninidin and luteolinidin. Addition of indoleacetic acid, kinetin and cofactors such as pyridoxine produced effects on the initiation and subsequent growth of these roots similar to those effects reported in the literature. But unlike root formation in hypocotyls, the initiation of adventitious roots in Sorghum internodes was not always directly correlated with the accumulation of anthocyanins, and the subsequent growth of these roots was frequently inversely correlated with some of the anthocyanin biosyntheses. The possible nature of these correlations is discussed. Comparisons are made with related Sorghum lines and mutants.

THE EFFECTS OF CALCIUM IONS AND pH ON THE DEVELOPMENT OF CALLUS TISSUE ON STEM CUTTINGS OF BALSAM POPLAR

This paper presents a comparative anatomical study of callus tissue produced on stem cuttings of balsam poplar (Populus balsamifera L.) grown in distilled water and in saturated solutions of CaSO4 from 6.0 to 11.0 pH. Striking differences in callus morphology, hardness, and cellular structure were observed. The fact that acidity retards and alkalinity accelerates the rate of calcification suggests that calcification or hardening of the middle lamellae could be a function of the rate at which the pectic acid component is neutralized.The emergence and subsequent growth of adventitious roots decreased markedly with increasing alkalinity, until at pH 11.0 most callus masses appeared to be rootless. However, sectioning usually revealed a well-developed root embedded some distance below the surface. Failure of most adventitious roots to emerge in a strongly alkaline calcium solution was attributed to the hard compact nature of the surrounding callus.

Studies on the Ripening of Wheat Grain : 7. Developmeht of embryo with special reference to the differentiation of seminal roots.

The differentiation and subsequent growth of seminal roots in the developing wheat embryo were investigated. At the 11th day after anthesis the primary seminal root was differentiated in the central portion of the embryo, when the coleoptile had already been initiated and the 1st foliage leaf was on the point of differentiation. At the 17th day, 2 days after the 2nd foliage leaf initiation, the 1st pair of seminal roots were initiated from the sides of the hypocotyl in a plane parallel to the face of the scutellum. At the 26th day, 2∼3 days after the 3rd foliage leaf initiation, the 2nd pair of seminal roots were initiated immediately above the 1st pair and in the same plane. On few cases the differentiation of the 6th seminal root from the middle point between the bases of the 2nd pair rootlets was observed at the 34th day. Most of the embryos, however, ceased their activity before the initiation of the 6th seminal root could be detected. The 3rd pair of seminal roots, whether their emergence occur after germination or otherwise, did not differentiate during the ripening stage of embryo. Based on these results the already recognized steps of embryo development were revised by including the developmental processes of seminal roots.

Factors Affecting Resistance to Heavy Grazing in Needle-and-Thread Grass

Needle-and-thread grass (Stipa comata Trin. et Rupr.) an important perennial mid-grass of the Great Plains, is generally considered as relatively sensitive to grazing injury (Sarvis 1923, Allred 1940, Lodge 1954). Nevertheless, this grass persisted in a very heavily grazed pasture, and maintained itself under less severe heavy grazing (Reed and Peterson, 1961) near Miles City, Montana. This observation relates to the relatively high degree of stability observed in the northern Great Plains vegetation under heavy grazing (Black et al 1937, Sarvis 1941, Clarke et al 1943) and has implications in respect to expected rate of change in plant size and to change in species composition as grazing pressure is maintained over a series of years. Changes in the size of plants and plant parts commonly occur in response to heavy grazing (Hanson et al 1931, Holscher 1945, Weaver and Darland 1947). There are apparently no reports to indicate the significance of these changes on plant resistance to grazing, except where this is complicated by secondary factors such as competition for light, water, etc. Shorter and more prostrate grass types, however, have been shown to resist heavy grazing better than taller types (Stapledon 1928, Kemp 1937). Slower spring growth by permitting an escape from the high grazing pressure common at that time, favors survival (Stapledon 1928). Resistance to grazing is considered to be associated with the ability of the plants to regenerate foliage tissues (Cook and Stoddart 1953). The significance of a given amount of regrowth to the plants' energy e c o n o m y would depend upon the ratio of leaf area to total size (including roots). Heavy grazing or clipping reduces subsequent growth of herbage and roots (Graber 1931, Biswell and Weaver 1933) the latter being reduced most. Because of the correlation between herbage production and root weight (Carter and Law 1948), relative size of tops will under similar circumstances give an estimate of relative size of roots. It was postulated that the persistence of needle-and-thread grass in the heavily grazed pasture might be favored by changes in responses to herbage removed (as compared to populations of the same species which had not been exposed to heavy grazing), or to changes in the genetic structure of the population. The specific objectives of the study were to ascertain if past grazing treatments influenced: (1) regrowth pattern after clipping and whether or not the pattern persisted with time; (2) regrowth pattern in the dark; and (3) plant populations as measured by transplant responses.

Selective Toxic Action of Thiosulphate on Plants

Investigations have been recently carried out on the effects of low concentrations of sodium thiosulphate on the germination and subsequent root growth of a number of plants. (These investigations were undertaken as a result of earlier work, not yet published, by Quastel, Hewitt arid Nicholas, on the effects of thiosulphate on growth of crops in soils.)