Primary Roots Of Seedlings Research Articles

Physiological potential of Phaseolus lunatus L. seeds subjected to water stress at different temperatures

Germination is negatively influenced by water scarcity and by temperatures above or below the optimal range of the species, so it is necessary to know the critical point of absorption for the species or cultivar. The objective of this work was to evaluate the effect of water stress, simulated by solutions of polyethylene glycol 6000 (PEG 6000) at different temperatures, on the germination and vigor of seeds of four cultivars (Branca, Orelha de Vó, Rosinha and Roxinha) of beans (Phaseolus lunatus L.). The water stress simulation was performed using PEG 6000 solutions at concentrations of 0.0, -0.2, -0.4, -0.6, -0.8, -1.0, and -1.2 MPa at temperatures of 25, 30, and 35 ° C. The analyzed variables were percentage of germination at first count, germination speed index, length of aerial part and primary root of seedlings, and dry mass of the respective parts of the seedlings. The seeds of the cultivar Orelha de Vó were more sensitive to water stress, with 88% germinating up to the potential of -0.6 MPa at the tested temperatures. The cultivars Branca, Rosinha, and Roxinha germinated (94, 100, and 100%, respectively) up to the potential of -0.8 MPa. Water stress simulated by PEG (6000) negatively affects seed twinning and seed vigor of bean cultivars.

Accelerated aging periods and its effects on electric conductivity of popcorn seeds

The production of popcorn has an increasing demand and requires the use of vigorous seeds. The accelerated aging test is used to evaluate seed’s vigor, promoting the disruption of the membrane system. The disruption of membranes can be evaluated by the electrical conductivity test. The objective of this study was to evaluate the effects caused by different periods of accelerated aging and the ions in the exudate of the electrical conductivity test and its interactions with the physiological quality of popcorn seeds. The experimental design was completely randomized with seeds being submitted to eight accelerated aging periods (zero, 24, 48, 72, 96, 120, 144 and 168 hours). Water content (%), first count of germination (%), final germination (%), germination speed index, electrical conductivity (μS cm-1 g-1) and length of aerial portion and primary roots of seedlings were evaluated. The germination and vigor of popcorn seeds and the amount of leachate in the electrical conductivity test were influenced by the increasing exposure period to accelerated aging. The period of 72 hours of exposure to accelerated aging produces results that reflect on the vigor potential and leachate of the seeds.

Potencial fisiológico de sementes de Clitoria fairchildiana R. A. Howard. - Fabaceae submetidas a diferentes regimes de luz e temperatura

Clitoria fairchildiana Howard, nativa da região amazônica, é bastante utilizada em programas de reflorestamento, na arborização de ruas, praças públicas, rodovias e estacionamentos, devido à sua copa larga e frondosa e ao seu rápido crescimento. Dessa forma, o objetivo neste trabalho foi estudar a influência de regimes de luz e temperaturas na germinação e no vigor de sementes de C. fairchildiana. Avaliou-se o potencial fisiológico das sementes sob temperaturas constantes (25 e 30°C) e alternada (20-30°C) em diferentes regimes de luz: branca, verde, vermelho-distante, vermelha e ausência de luz. O delineamento experimental foi inteiramente casualizado, em esquema fatorial 3x5, em quatro repetições. As variáveis analisadas foram: porcentagem de germinação, primeira contagem e índice de velocidade de germinação (IVG), bem como comprimento e massa seca de parte aérea e raízes das plântulas. As sementes de C. fairchildiana germinam no escuro e em todos os regimes de luz, independente da temperatura utilizada, sendo consideradas fotoblásticas neutras. Para avaliação do vigor dessas sementes, recomenda-se a temperatura de 30°C no regime de luz branca.

Resistance reaction of conifer species (European larch, Norway spruce, Scots pine) to infection by selected necrotrophic damping-off pathogens

Three conifer species (European larch, Norway spruce, Scots pine) were investigated for their resistance to five damping-off pathogens (Rhizoctonia solani, Fusarium solani, F. oxysporum, F. culmorum, F. avenaceum). Inoculation of the primary roots of seedlings with these pathogens caused host cell death which did not prevent the invasive growth of these fungi; seedlings that had formed secondary and tertiary roots could overcome the infection to a significant degree. Infections with R. solani caused significant mortality to all the conifer species. In contrast, the tree species expressed different levels of resistance when challenged with the Fusarium isolates, with Norway spruce being the most resistant compared to uninoculated controls. Some of the Fusarium isolates were more pathogenic to certain hosts than others; F. oxysporum for European larch, F. avenaceum for Scots pine, F. solani for European larch; only F. culmorum was significantly pathogenic to Norway spruce. No significant differences in disease severity were observed at different soil pH (4.3–7.5). Disease progression was delayed at lower (10–15°C) rather than higher temperatures (20–25°C).

Vesicular‐arbuscular mycorrhizal infection of grass seedlings in a degraded semi‐arid savanna in Botswana

Infection of eight indigenous grasses with vesicular-arbuscular mycorrhizal (VAM) fungi was studied in a savanna in South-eastern Botswana. Infection of seedlings with VAM fungi was rapid just after germination at the onset of the rainfall season. Particularly high infection levels were found in the primary roots of seedlings but levels temporarily dropped with the development of the secondary roots. In 30 % of all cases germinating spores were found to be the source of infection, suggesting an important role for them in semi-arid grasslands. The inoculum potential of soils from eroded and non-eroded sites in the study area was compared. Subsoil was found to have a lower inoculum potential than topsoil. Topsoil from an eroded site without vegetation showed a lowered inoculum potential compared to sites with vegetation present. Topsoil from unvegetated sites where soil material was deposited however, did not always show a lower inoculum potential. This indicates that the transport and redistribution of water and soil material does not automatically result in lower infection levels.

A statistical study of the formation of lateral roots in Pisum sativum L. under constant conditions

The dynamics of the germination and formation of lateral roots under constant conditions were studied in pea Pisum sativum L., cv. Pyram. Various parameters of the above processes were evaluated statistically. The time at which the germination proceeds at the maximum rate was found to be 24·9 h from the start of the imbibition of seeds. The standard deviation of the germination time of an individual seed from the time corresponding to the maximum of germinated seeds was found to be 4·0 h. The formation of the lateral root primordia took place at 54·2 ± 2·9 h. At 73·5 ± 5·5 h from the beginning of the experiment, laterals on the surfaces of primary roots of seedlings became apparent. Differential curves of the distribution of the above processes were plotted graphically. The data obtained are valid for the given conditions and given experimental procedure. The methods described can be used in studies of primary root branching in various plant species.

DEVELOPMENTAL STUDIES ON EUPHORBIA ESULA L.: MORPHOLOGY OF THE ROOT SYSTEM

The significance of Euphorbia esula L. as a weed is related to its capacity to persist under adverse conditions and to its mode of reproduction. In both these properties, the root system plays an important role. The root system is initially established by seedlings. The seedling has a vigorous primary root with extensive longitudinal growth and considerable cambial activity. Such a root has been designated a "long" root. By contrast, the first lateral roots produced on the primary root have limited growth and no cambial activity. These roots have been termed "short" roots. Thus, the seedling exhibits a "heterorhizic" pattern. Lateral long roots also arise on the primary root of seedlings but their origin is delayed until cambial activity has begun. Such lateral long roots arise much earlier on seedlings growing in denuded areas than on those growing in areas covered by dense vegetation. The mature root system is described in terms of horizontal and vertical long roots, which make up the conspicuous framework of the system, and of the short roots which they produce. Long roots produce shoot-buds and the origin of these structures is delayed until cambial activity has started. Short roots do not give rise to shoot-buds. Cambial activity in long roots appears to be connected with bud production and its absence in short roots probably underlies their inability to produce buds.L'importance de Euphorbia esula L. comme mauvaise herbe est connexé a son capacité de persister dans les situations hostiles et à sa methode de reproduction. Dans ces deux caractéristiques, le système des racines a une signification profunde. Initialement le système des racines s'établit dans le semis. Le semis a une racine primaire très forte avec beaucoup de croissance longitudinale et avec une activité considérable du cambium. Une racine de cette espèce s'appelle une "longue" racine (long root). Par contre, les premières racines latérales que poussent sur la racine primaire ont croissance limité et aucun activité du cambium. Ces racines s'appellent les "courtes" racines (short roots). De cette façon, le semis montre un dessin "heterorhizique" (heterorhizic). Les longues racines latérales ont aussi leur origine sur la racine primaire du semis, mais l'origine est retardé jusqu'au commencement de l'activité du cambium. Les racines de cette espèce apparaissent beaucoup plus tôt sur les semis qui sont situés en terre sans autre végétation, que sur ceux qui sont situés au milieu des autres plantes. Le système adulte des racines se décrit sous forme des longues racines de l'espèce horizontale et verticale, lesquelles constituent la charpente bien visible du système, et des courtes racines que sont produites par les longues racines. Les longues racines produisent les bourgeons, mais l'origine des bourgeons est retardé jusqu'au commencement de l'activité du cambium dans les racines. Les courtes racines ne produisent pas les bourgeons. Il paraît que l'activité du cambium dans les longues racines soit corrélative avec l'initiation des bourgeons et l'absence du cambium dans les courtes racines explique probablement leur incapacité à produire les bourgeons.