Rapid Seedling Growth Research Articles

Combined effects of cotyledon excision and nursery fertilization on root growth, nutrient status and outplanting performance of Quercus variabilis container seedlings.

Artificial excision of the distal part of acorns in order to promote germination is well researched in oak seedling cultivation studies. However, studies of combined effects of cotyledon excision and nursery fertilization on container seedlings are lacking, especially for seedling root growth and outplanting performance. This study aimed to explore the main effects of cotyledon excision on Quercus variabilis seedling emergence characteristics and demonstrated the combined effects of cotyledon excision and nursery fertilization on seedling quality to improve Quercus variabilis seedling outplanting performance. Four cotyledon excision treatments and two classes of nursery fertilization were implemented. Seedling emergence was noted every week after sowing. Seedling dry mass, morphology, and nutrient status were assessed at the end of the nursery season. After the first outplanting season, the aforementioned measurements along with seedling survival were determined once again. The results showed that cotyledon excision generally induced greater and more rapid seedling emergence, but did not affect shoot emergence synchronicity. The highest total emergence and emergence rate occurred with Intermediate excision (1/2 of the distal end of acorn was excised). Effects of nutrient loss due to cotyledon excision on seedling quality and outplanting performance were somewhat compensated by nursery fertilization. Nursery fertilization promoted dry mass increment (the net increment from T0 to T2 for dry mass) for excised seedlings after outplanting, resulting in better performance for Slight (1/3 of the distal end of acorn was excised) and Intermediate excision treatments in the field. Thus we conclude Intermediate excision combined with reasonable nursery fertilization can be recommended for production of nursery grown seedlings for afforestation.

Tarping and Inundation as Potential Control Mechanisms for Seed Banks of Red Sesbania (Sesbania punicea)

The exotic shrub red sesbania is an increasingly problematic weed in riparian and wetland ecosystems of California. Current control methods focus on manual removal, followed by herbicide application. Although this method effectively removes mature stands, the control is temporary because the presence of a large seed bank results in rapid germination and growth of new seedlings. We measured the density of seed banks beneath stands of varying densities and evaluated the potential of tarping and inundation for control of red sesbania seed banks. As expected, the abundance of viable red sesbania seeds in the soil was significantly greater beneath high-density stands than it was beneath low-density stands. Results for inundation and tarping experiments were mixed. Sustained inundation significantly decreased survivorship of germinated seeds compared with the control, as well as causing a statistically significant reduction in germination. Seven months after tarping, during the fall/winter growing season, there was no significant effect on red sesbania seedling abundance, stump resprout abundance, or height. Germination in the laboratory was significantly reduced by extended exposure to temperatures of 60 C, although lower temperatures did not reduce germination. Red sesbania appears to be resilient to tarping as a control method, at least in the settings studied.

The Transcription Factor ATHB5 Affects GA-Mediated Plasticity in Hypocotyl Cell Growth during Seed Germination.

Gibberellic acid (GA)-mediated cell expansion initiates the seed-to-seedling transition in plants and is repressed by DELLA proteins. Using digital single-cell analysis, we identified a cellular subdomain within the midhypocotyl, whose expansion drives the final step of this developmental transition under optimal conditions. Using network inference, the transcription factor ATHB5 was identified as a genetic factor whose localized expression promotes GA-mediated expansion specifically within these cells. Both this protein and its putative growth-promoting target EXPANSIN3 are repressed by DELLA, and coregulated at single-cell resolution during seed germination. The cellular domains of hormone sensitivity were explored within the Arabidopsis (Arabidopsis thaliana) embryo by putting seeds under GA-limiting conditions and quantifying cellular growth responses. The middle and upper hypocotyl have a greater requirement for GA to promote cell expansion than the lower embryo axis. Under these conditions, germination was still completed following enhanced growth within the radicle and lower axis. Under GA-limiting conditions, the athb5 mutant did not show a phenotype at the level of seed germination, but it did at a cellular level with reduced cell expansion in the hypocotyl relative to the wild type. These data reveal that the spatiotemporal cell expansion events driving this transition are not determinate, and the conditional use of GA-ATHB5-mediated hypocotyl growth under optimal conditions may be used to optionally support rapid seedling growth. This study demonstrates that multiple genetic and spatiotemporal cell expansion mechanisms underlie the seed to seedling transition in Arabidopsis.

Notice of Release of 'Trailhead II basin wildrye

‘Trailhead II’ basin wildrye ( Leymus cinereus (Scribn. & Merr.) A. Love [Poaceae]) is a tetraploid basin wildrye release for use in re-vegetation efforts on rangelands of western North America. Trailhead II is the result of 2 cycles of recurrent selection within the basin wildrye cultivar ‘Trailhead’ for rapid seedling emergence from deep seeding. Trailhead II is genetically distinct from Trailhead. Additionally, in comparisons between Trailhead II and Trailhead, Trailhead II possessed higher total emergence and more rapid emergence from deep seeding (7.6 cm [3 in]) and exhibited higher seedling establishment at 3 of 5 field sites where it was evaluated in Nevada, Utah, and Wyoming. The release of Trailhead II basin wildrye improves this native germplasm to enhance the success of conservation and re-vegetation plantings in the Intermountain West and Northern Great Plains areas of the US and Canada.

QTLs for Early Tiller Production and Relationships with Rapid Seedling Growth and Increased Panicle Number in Rice

Tiller number (TN) is a key determinant of final grain yield in the small grains crops, including rice (Oryza sativa L.), and is desired to enhance competition with weeds. Quantitative trait loci (QTLs) associated with TN were mapped within a set of recombinant inbred lines developed from a cross between the low‐tillering tropical japonica cultivar ‘Kaybonnet‐lpa1‐1’ and the high‐tillering, high‐yielding, early‐maturing indica cultivar ‘Zhe733’ using data collected from greenhouse potted plants evaluated weekly. Relationships between the five identified TN QTLs and related traits including panicle number (PN), flag leaf number, seedling leaf number (SLN), and earliness of tiller production were also evaluated. The three TN QTLs that were linked with early tiller emergence were also associated with PN; two additional TN not associated with PN were also identified. All five TN QTLs were also SLN QTLs, though other loci affecting SLN were also identified. Several of the TN and SLN QTLs identified using data from young plants (e.g., ≤6 wk after planting) were not detectible in data collected just before or after heading. The three TN QTLs also associated with PN showed stronger effects (higher logarithm of the odds ratios and additive effects) on TN as observed in seedling stages than on final TN at heading time, and their effects diminished over time to the point that they were not always detectible in TN data collected at or after heading. However, the three TN QTLs that were also PN QTLs were robust enough that they were detected in the less intensive (one‐fourth the labor and resources) Arkansas trials, where tillers were counted from two single‐plant replications just twice, at 6 wk after planting and after heading. The three loci associated with both TN and PN are the TN loci most likely to increase rice yield, and the markers presently found linked to them can be used for marker assisted breeding.

Dynamic response of a Philippine dipterocarp forest to typhoon disturbance

AbstractQuestionsNatural hazards can wreak catastrophic damage to forest ecosystems. Here, the effects of typhoon disturbance on forest structure and demography of the 16‐ha Palanan Forest Dynamics Plot in the northeast Philippines were examined by comparing census intervals with (1998–2004) and without (2004–2010) a strong typhoon. Category 4 Typhoon Imbudo, with wind gusts exceeding 210 kph, hit Palanan in July 2003. In this study, we ask: (1) was there an effect of the typhoon on stand structure and biomass; (2) was there an impact on species diversity; (3) did annual mortality, growth and recruitment change significantly between typhoon and non‐typhoon periods; and (4) did the typhoon's impact vary with local topography, from leeward to windward sides of a ridge?LocationLowland mixed dipterocarp forest, Palanan, Isabela, Philippines.MethodsCensus data from 1998, 2004 and 2010 for all trees ≥1 cm DBH in a 16‐ha permanent plot in Palanan, Isabela, were used to assess tree demography. Recorded in the census were species identification and measurements of DBH and tree locations. Biomass was calculated from published allometry.ResultsSpecies diversity and stand structure remained stable, except for an increase in small‐sized trees (1–2 cm) recorded in the census conducted within a year of the typhoon disturbance. Tree mortality was significantly higher during the typhoon interval at 2.27%·yr−1 and more so in windward than leeward habitats. Above‐ground biomass loss in the typhoon interval was minimal (2.64%) and biomass exceeded pre‐typhoon levels after 6 yrs. Recruitment rate during the typhoon interval was almost four times the rate in the non‐typhoon interval that followed, attributed to the rapid growth of seeds and seedlings of pioneer species due to the open, defoliated canopy. Negative population growth was recorded for the early successional species in the non‐typhoon interval. Significantly higher growth rates of trees in the non‐typhoon interval also contributed to biomass gain.ConclusionsMortality, recruitment and growth rates vary across a heterogeneous landscape and are related to typhoon disturbances. The relatively low mortality and fast recovery of the Palanan forest demonstrates the resistance and resilience of the forest to intense episodic typhoon disturbances.

FEATURES OF THE PHENOLICS’ FORMATION IN SEEDLINGS OF DIFFERENT VARIETIES OF BUCKWHEAT (Fagopyrum esculentum Moench)

Abstract A unique feature of higher plants is the capacity to form phenolic compounds, the sub-stances with high antioxidant activity. These secondary metabolites play an important functional role, including cell and tissue protection against stress factors. It is especially important at the initial stages of plant ontogenesis. Buckwheat (Fagopyrum esculentum Moench) is the major cereal crop for which the formation of various phenolics, particularly rutin, a biologically active compound of plant origin successfully used in pharmacology, is characteristic. In the young seedlings (at the age of 14 days) of 10 buckwheat varieties mostly bred in Russian research centers during recent decades we studied the morphophysiological parameters and the accumulation of phenolic compounds, in-cluding phenylpropanoids and flavonoids, in the hypocotyls and cotyledons. Particularly, the highest level of phenylpropanoids was found in Bol’shevik 4 and Bashkirskaya krasnostebel’naya varieties. Note, it was high and almost equal in the hypocotyls and cotyledons. In the rest varieties the amount of phenylpropanoids in seedlings was 20 to 50 % lower, and in the cotyledons it was 1.5-2.0 times higher compared with the hypocotyls. Accumulation of flavonoids was higher in the Dialog variety, somewhat lower in Bol’shevik 4 and Bashkirskaya krasnostebel’naya varieties (by 10 and 17 %, re-spectively), and 35 to 40 % lower in the other studied forms. The highest content of anthocyanins was shown in the Bashkirskaya krasnostebel’naya plants, while in other studied buckwheat varieties it was lower. Particularly, in Devyatka, Bol’shevik 4 and Temp plants a decrease was about 50 %, and in Batyr, Dialog, Chatyr tau, Ilishevskaya, Dizain, and Dikul’ varieties 70 to 80 % decrease was found. It was shown that recently bred buckwheat varieties have a very rapid growth and develop-ment of seedlings, which is important for their better adaptation in the early ontogeny. The most promising varieties, along with Bashkir krasnostebelnaya, are Bolshevik 4, Nine, Dialogue and Tempo. They are characterized by a high capacity for accumulation the phenolic compounds, the important components of the antioxidant defense system in plants. This feature of their metabolism may be a potential criterion for plant resistance to stress factors Keywords: buckwheat, Fagopyrum esculentum Moench, varieties, phenolic compounds, phenylpropanoids, flavonoids, anthocyanins.

Biogenic nanoparticle-mediated augmentation of seed germination, growth, and antioxidant level of Eruca sativa mill. varieties.

A study was undertaken to examine the influence of biogenic nanoparticles synthesized from Tridax procumbens on different parameters of seed germination, seedling growth, and various biochemical parameters in four Eruca sativa varieties having low percentage of germination. Seeds were treated with different concentrations (30 and 40 ppm) of biogenic nanoparticles, of which 30 ppm was found to be the most effective and was therefore used for subsequent studies. Initially, the effect of biogenic nanoparticles on germination percentage, speed of germination, coefficient of germination, mean germination time, shoot and root length, fresh and dry matter, and vigor index was studied. From the experiments performed and the results obtained, it was evident that the treatment with biogenic nanoparticles decreased the electrolyte leakage and level of malondialdehyde as compared to control. The treatment with biogenic nanoparticles enhanced the levels of proline and ascorbic acid and stimulated the antioxidant enzyme activities resulting in the reduced level of reactive oxygen species. These activities were found to be variety-dependent. The possible involvement of biogenic nanoparticles in the production of new pores in seed coat during their penetration, resulting in the influx of the nutrients inside the seed, is suggested. This accelerated seed germination is followed by rapid seedling growth. The present findings indicated that biogenic nanoparticles promote seed germination in E. sativa by overcoming the detrimental effects of reactive oxygen species (ROS) and improving the antioxidative defense system which finally result in increased seedling growth.

Comparative growth, dry matter accumulation and photosynthetic rate of seven species of Eucalypt in response to phosphorus supply

Plantations of eucalypts as short-rotation tree crops are rapidly expanding in tropical and sub-tropical regions, including southern China, where the soils are acidic and available phosphorus (P) is limited. We investigated seedling growth, dry matter accumulation, and the dynamics of photosynthetic rate and chlorophyll content of seven Eucalyptus species/hybrids (E. dunnii, E. grandis, E. grandis × E. camaldulensis, E. urophylla × E. camaldulensis, E. urophylla × E. tereticornis, E. grandis × E. tereticornis, E. urophylla × E. grandis) in response to different levels of P supply (0, 6, 12 and 18 mg·kg−1 KH2PO4). The photosynthetic rate and the chlorophyll content significantly declined as the P supply declined in almost a linear fashion for all species as the P stress period extended. In the absence of P supply, height growth of seedlings of all species was significantly impaired, while root collar diameter growth and whole plant dry matter accumulation was not affected by the level of P supply in most of the species. Significant inter-species variations in growth, dry matter accumulation and photosynthetic rate in response to P supply were detected. Eucalyptus dunnii had the lowest growth performance across all levels of P supply while E. Urophylla × E. tereticornis showed superior growth performance. From a practical point of view, E. Urophylla × E. tereticornis is suggested as a candidate hybrid for planting on slightly P-deficient sites in southern China while E. dunnii, being a slow-growing species, is not suitable for short-rotation plantation. On plantation sites where severe P deficiency exists, P fertilization needs to be considered to boost rapid growth of seedlings so as to meet the management objectives of short-rotation plantation.

Variation in phenotypic plasticity for native and invasive populations of Bromus tectorum

Phenotypic plasticity is often considered important for invasive plant success, yet relatively few studies have assessed plasticity in both native and invasive populations of the same species. We examined the plastic response to temperature for Bromus tectorum populations collected from similar shrub-steppe environments in the Republics of Armenia and Georgia, where it is native, and along an invasive front in California and Nevada. Plants were grown in growth chambers in either ‘warm’ (30/20 °C, day/night) or ‘cold’ (10/5 °C) conditions. Invasive populations exhibited greater adaptive plasticity than natives for freezing tolerance (as measured by chlorophyll a fluorescence), such that invasive populations grown in the cold treatment exhibited the highest tolerance. Invasive populations also exhibited more rapid seedling emergence in response to warm temperatures compared to native populations. The climatic conditions of population source locations were related to emergence timing for invasive populations and to freezing tolerance across all populations combined. Plasticity in growth-related traits such as biomass, allocation, leaf length, and photosynthesis did not differ between native and invasive populations. Rather, some growth-related traits were very plastic across all populations, which may help to dampen differences in biomass in contrasting environments. Thus, invasive populations were found to be particularly plastic for some important traits such as seedling emergence and freezing tolerance, but plasticity at the species level may also be an important factor in the invasive ability of B. tectorum.

Growth and root development of black and white spruce planted after deep planting

The capacity of trees to produce new roots is essential for rapid early growth of planted seedlings. Black and white spruce trees (Picea mariana and Picea glauca) are widely planted in the eastern boreal forest of Canada and are known to develop substantial adventitious root systems. In this study, we compared root development and growth of 17-year-old trees that had been planted at two different depths (ground level vs 10–12cm) to see if partial stem burial would hasten adventitious root development, and in turn, growth. Root number (total and adventitious), root total area, rooting depth, year of root formation, tree height and basal diameter were measured in black and white spruce trees. Both species developed adventitious root systems, and adventitious roots size and area were greater for deeply planted trees than for trees planted at ground level. The number of adventitious roots and the speed of adventitious root development were greater for deeply planted black spruce but not for deeply planted white spruce, compared with trees planted at ground level. For the latter, site conditions could explain the absence of a planting depth response. Deep planting increased tree height and basal diameter of white spruce, but only height for black spruce trees. However, tree growth was related to total root cross-sectional area (not just adventitious roots), underscoring the importance of both types of roots for tree growth.

Root endophytes enhance stress‐tolerance of Cicuta virosa L. growing in a mining pond of eastern Japan

AbstractCicuta virosa L. plants can grow in a pond subjected to heavy‐metal inputs at the Hitachi mine, eastern Japan. They accumulate heavy‐metal elements, especially high concentrations of zinc (Zn), in their roots. We focused on the role that root bacterial endophytes play in the heavy‐metal uptake of plants and the provision of heavy‐metal tolerance within plants. Our purpose was to clarify the effects of endophytes on: (i) Zn accumulation in C. virosa roots; (ii) growth of C. virosa seedlings; and (iii) heavy‐metal tolerance of C. virosa plants. Root endophytic Pseudomonas putida and Rhodopseudomonas sp., which induced the high production of Zn‐chelating compounds, were selected for the seedling inoculation test. The results of the inoculation test demonstrated that both strains of endophytes increased Zn accumulation in C. virosa roots by solubilizing Zn in the sediment. Both strains also increased the growth of seedlings by possible production of indole‐3‐acetic acid in the plant. The heavy‐metal tolerance of C. virosa seedlings was likely promoted by producing metal‐chelating compounds that detoxify the metals in the plant tissues, and by decreasing the heavy‐metal contents in the tissues via rapid seedling growth. Thus, such mutualistic interactions between plants and bacteria contribute to the persistence of C. virosa in this severe environment.

Influence of vesicular arbuscular mycorrhiza (VAM) and phosphate solubilizing bacteria (PSB) on growth and biochemical constituents of Marsdenia volubilis

A field experiment was carried out to find out the effect of biofertilizers, vesicular arbuscular mycorrhiza (VAM), and phosphate solubilising bacteria (PSB) individually and in combination on growth and physiological attributing properties of Marsdenia volubilis plant under nursery conditions. The plant seedlings were harvested at various intervals: 30, 60 and 120 days after transplantation. The inoculation of microbial cultures VAM and PSB resulted in enhancement of growth parameters like plant height, root length, fresh weight and dry weight of shoot and root, leaves/plant, leaf area/plant , chlorophyll content, reducing and non-reducing sugars, starch, lipid and protein contents in root and shoot samples. These parameters were maximum with dual inoculation than individually. The results emphasize the importance of microbial biofertilizers inoculations for rapid growth of seedlings of plant ( M. volubilis ) in nurseries and illustrate the advantage of inoculating soils of low microbial population with indigenous microbes. Keywords: Biofertilizers, vesicular arbuscular mycorrhiza (VAM), phosphate solubilising bacteria (PSB), Marsdenia volubilis , growth and biochemical parameters. African Journal of Biotechnology Vol. 12(38), pp. 5648-5654

Volume de substrato e idade: influência no desempenho de mudas clonais de eucalipto após replantio

O rápido crescimento inicial das mudas é um ponto crítico para o sucesso da plantação florestal. Neste estudo, objetivou-se avaliar a influência da idade e do volume de substrato utilizado na produção de mudas clonais de Eucalyptus urograndis no desempenho após o replantio. O experimento foi conduzido em blocos casualizados com dez repetições, no arranjo fatorial 2 x 4 (mudas clonais produzidas em tubetes de 53 e 180 cm³ e com quatro idades - 60, 75, 90, e 120 dias) no espaçamento 3 x 3,33 m. Como tratamento adicional, avaliaram-se plantas de um plantio comercial, plantadas 20 dias antes da instalação do experimento. A utilização de mudas para replantio produzidas com maior volume de substrato possibilitou melhor crescimento inicial em campo. Entretanto, aos 12 meses de idade, o crescimento das mudas de replantio não foi influenciado pela idade e nem pelo volume de substrato utilizado para a produção das mudas.

Teste de envelhecimento acelerado para avaliação do potencial fisiológico de sementes de grama-bermuda

A utilização de sementes para formação de gramados esportivos e ornamentais tem assumido grande importância no Brasil, principalmente pelo baixo custo em relação à formação por placas de tapetes naturais. As "bermudas" [Cynodon dactylon (L.) Pers] são as principais gramas utilizadas na formação de campos esportivos e, dentre os problemas enfrentados, destaca-se a dificuldade de estabelecimento adequado da cultura, fato que exige a utilização de sementes de alto potencial fisiológico, de modo a permitir rápida emergência e desenvolvimento das plantas. Assim, estudaram-se procedimentos para a condução do teste de envelhecimento acelerado para determinar o potencial fisiológico de sementes dessa espécie, incluindo a avaliação da eficiência do uso de solução saturada de NaCl como alternativa para a realização do teste. Para tanto, cinco lotes de sementes foram submetidos aos testes de germinação, emergência de plântulas e envelhecimento acelerado (períodos de 48, 72 e 96 h, a 41 e 45 ºC, com e sem o uso de solução saturada de NaCl). O experimento foi conduzido em delineamento inteiramente casualizado. O envelhecimento acelerado com o uso de solução saturada de NaCl, dentre os procedimentos estudados, é o método mais adequado para avaliação do potencial fisiológico de sementes de grama-bermuda, sendo que a combinação 45 ºC/48 h é eficiente para a classificação dos lotes em diferentes níveis de vigor.

Influences of seedling size, container type and mammal browsing on the establishment of Eucalyptus globulus in plantation forestry

Rapid early growth of tree seedlings is critical to the success of plantation establishment. We investigated the effects of seedling size (small and large) and container types (small [Lannen 121], medium [Lannen 81] and large [Forestry Tube]) in the nursery and the effects of mammal browsing after planting on growth of Eucalyptus globulus in Tasmania’s Southern Forests. After planting, seedlings were either exposed to browsing or protected from browsing by wire-mesh cages until age 6 months. Low browsing pressure resulted in around 20% and 5–10% of foliage being browsed in the large and small size categories, respectively, between 1 and 3 months after planting the uncaged treatment. 6 months after planting, height growth increment was lower, and 4 years after planting, mortality was higher in uncaged large than caged large seedling treatments. Six and twelve months after planting, seedlings raised in Forestry Tube containers had significantly greater height increment and root collar diameter relative to other treatments. By 4 years after planting, trees of the small seedling treatment had significantly greater diameter than those of the large seedling treatment, but there was no effect of container type treatment. Four years after planting there was no effect on diameter growth by browsing of <30% of foliage up to 3 months after planting, although there was greater incidence of double leaders in trees that had been browsed as seedlings. Small seedlings produced more growth 4 years after planting than large seedlings of E. globulus.

Dispersal and demography contributions to population spread of Carduus nutans in its native and invaded ranges

Summary Invasive species usually exhibit different spatial population dynamics in their native and invaded range. This is often attributed to demographic differences, but may be due to differences in dispersal as well. Regardless of how these dispersal and demographic differences from the native range arose, studying how they contributed to increases in population spread rates will increase our understanding of what has made these species invasive. Here we investigate which vital rates and dispersal parameters of the invasive thistle Carduus nutans drive the increases in spread rate in different invaded ranges compared to that in the native range in Eurasia. We construct and analyse spatial integrodifference models that combine structured, local population models with mechanistic (WALD) models of seed dispersal by wind across a homogeneous landscape. Published and new demographic and dispersal data for single populations from the native (France) and invaded (Australia, New Zealand, Kansas and Pennsylvania) ranges were used for the parameterization. We developed a variance decomposition method (c*‐LTRE) to analyse the contributions of the changes in the vital rates and dispersal parameters to the increases in the invasion wave speed (c*) estimates for the different invaded ranges compared to that for the native range. The c*‐LTRE analysis showed that the net contribution of the dispersal parameters to c* increases varied among the populations from 51% (Australia), to 79% (Kansas), to 80% (New Zealand) and to 85% (Pennsylvanian experiment). Escape from natural enemies that reduce seed set by floral herbivory was important in all invaded ranges. Large positive contributions were also made by increases in rapid growth of seedlings and small rosettes, increases in flowering probabilities and potential seed production, as well as by increased plant height and lower falling velocities of the plumed seeds. Synthesis. By incorporating a mechanistic dispersal model with a structured population model, and by linking this joint model to field data from several continents, we demonstrate the relative importance of dispersal and demography to invasion success. This approach can be used to analyse which aspects of an invader's life history have changed most importantly from the native range.

Inheritance of coleoptile tiller appearance and size in wheat

Selection for rapid leaf area growth has the potential to increase wheat biomass, and both water-use efficiency and weed competitiveness early in the season. Several morphological components contribute to increased seedling leaf area, including rapid seedling emergence and production of longer, wider leaves. Early emergence of a large coleoptile tiller has also been demonstrated to increase plant leaf area and biomass in wheat and other grass seedlings. Yet little is known of the extent and nature of genotypic variation for coleoptile tiller growth in wheat. A random set of 35 wheat, barley, and triticale genotypes was evaluated in glasshouse and outdoor studies for seedling characteristics, including coleoptile tiller growth and total plant leaf area. Coleoptile tillers were produced more reliably for seedlings grown outdoors and when supplied with additional soil nitrogen. Genotypic differences in coleoptile tiller frequency and leaf area were large, ranging from 0 to 78% and from 0.0 to 1.4 cm2, respectively at very early growth stages. Australian commercial wheats tended to produce fewer coleoptile tillers of smaller size than overseas germplasm where the coleoptile tiller accounted for up to 12% of total seedling leaf area. This compared favourably with mainstem tiller leaf area, which ranged from 0 to 3.5 cm2 and accounted for up to 16% of plant leaf area. Broad-sense heritabilities were high for coleoptile tiller presence and size in favourable conditions (c. 75%) but low (c. 40%) for seedlings evaluated across nitrogen content-varying soils. Generation means analysis was used to investigate genetic control for coleoptile tiller growth across multiple populations. Significant (P &lt; 0.05) differences were observed among generations for coleoptile tiller frequency and growth (numbers of leaves, leaf area, and biomass). These differences reflected strong additive genetic control with little evidence for any gene action × year interaction. Increases in coleoptile tiller frequency and mass were correlated with larger embryo size and wider seedling leaves to increase seedling leaf area (rg = 0.89). Comparisons between reciprocal F1 and F2 generation means indicated strong maternal effects for coleoptile tiller growth in some but not all crosses. Screening in favourable environments will increase heritability and aid in selection for progenies producing large coleoptile tillers. Evidence for additive genetic control should permit early generation selection but not without some progeny-testing for coleoptile tiller growth together with other early vigour components associated with increased plant leaf area.

Impact of red : far red ratios on germination of temperate forest herbs in relation to shade tolerance, seed mass and persistence in the soil

Summary The effect of the ratio of red : far red light (R : FR) on seed germination of herbaceous species from northern temperate deciduous forest has received little attention. Here for 27 such species, we investigated the relationship between seed mass and the suitability of micro‐sites for germination. Germination in light and in darkness was compared after cold stratification, and for the light‐requiring species, the germination response to R : FR was determined. In addition, seed bank persistence was monitored over 4 years. With increasing seed mass, germination became less dependent on light and seed bank persistence decreased. Furthermore, for the light‐dependent species, there was a significant negative relationship between the R : FR that resulted in 50% germination and seed mass. These data suggest that small‐seeded species only germinate in micro‐sites with a high R : FR, which signals the absence of over‐topping vegetation or leaf litter. Such micro‐sites are comparatively rare, which may necessitate persistence in the soil seed bank. For small‐seeded species, we propose that a key benefit from restricting germination to high R : FR is a reduction in the time‐frame over which the initially small seedlings remain small and hence highly vulnerable to mortality: high R : FR is likely to indicate high‐light levels which would facilitate rapid seedling growth.

Influence of temperature and watering frequencies on seed germination and seedling growth of Ornithogalum longibracteatum and Tulbaghia violacea

The effect of temperature and watering frequencies on seedling growth were investigated in Ornithogalum longibracteatum and Tulbaghia violacea. Temperature had a significant influence on seed germination with low (10 °C) and high (40 °C) temperatures resulting in poor germination in both species. The optimum temperature for seed germination of O. longibracteatum and T. violacea was 22.9 and 26.8 °C, respectively. Seedling survival rate for both species was higher at temperatures ranging from 10 to 25 °C. Bulb fresh weight of seedlings grown at 15–25 °C was significantly higher than for seedlings subjected to 30 and 35 °C. Leaf length increased with higher temperature. The highest number of roots was recorded at 25 °C in both species. Watering had a pronounced positive effect on the seedling survival percentage and seedling growth of O. longibracteatum and T. violacea. Watering three times a week (W3) resulted in rapid seedling growth compared to watering once or twice a week. These findings suggest that a combination of temperature (25 °C) and frequency of watering of the seedlings will result in better seedling quality for field planting.