Stem Extension Rate Research Articles

Development of a lucerne model in APSIM next generation: 1 phenology and morphology of genotypes with different fall dormancies

Prediction of lucerne phenological and morphological development is important for optimising the defoliation schedule and time of other management events. A challenge for any lucerne phenology module is to capture the seasonality of development processes in response to environment, management and genotype. To date, lucerne phenological modules have not been evaluated under different defoliation regimes or with genotypes of different fall dormancy (FD) classes. This research integrated data of lucerne phenological development into the Agricultural Production Systems sIMulator (APSIM) next generation (APSIM NextGen) model framework to develop and verify a phenology module. Relationships derived from the FD5 genotype, grown under a 42 day (LL) defoliation treatment were used for model development. These were further tested for two genotypes with contrasting FD (FD2 and FD10) under frequent (28 day: S) or long (84 day: H) defoliation regimes, all under irrigated conditions. Development was parameterized based on thermal time targets to reach specific phenological stages and modified by photoperiod responses. Development stage and node appearance were shown to be independent of defoliation treatment and FD class. Simulation results showed good agreement for prediction of development stages (NSE of 0.77 for days to buds visible and 0.67 for days to flowering stage) and number of main stem nodes (NSE values were ranged from 0.53 to 0.84). However, both defoliation management treatment and FD classes affected stem height. For FD5, there was good agreement for the 84 day treatment (NSE of 0.83) and the 42 day treatment (NSE of 0.66), but it was poor for the 28 day treatment (NSE of -0.08). This was probably due to reduced stem extension rates, limited by low C and N reserves in perennial organs under the frequent (28 day) defoliation regime. For FD2 and FD10, two separate sets of parameters were used to improve model prediction of height to account for their contrasting seasonal C partitioning patterns. These results show that the APSIM NextGen lucerne phenology module was able to simulate crops grown under unconstrained growing conditions. However, the reason for under estimation of stem height for the 28 day treatment needs further investigation.

Exogenous Silicon Enhanced Salt Resistance by Maintaining K+/Na+ Homeostasis and Antioxidant Performance in Alfalfa Leaves.

Silicon (Si) has been known to enhance salt resistance in plants. In this experiment, 4-weeks-old alfalfa seedlings were exposed to different NaCl concentrations (0–200 mM) with or without 2 mM Si for two weeks. The results showed that NaCl-stressed alfalfa seedlings showed a decrease in growth performance, such as stem extension rate, predawn leaf water potential (LWP) and the chlorophyll content, potassium (K+) concentration, as well as the ratio of potassium/sodium ion (K+/Na+). In contrast, NaCl-stressed alfalfa seedlings increased leaf Na+ concentration and the malondialdehyde (MDA) level, as well as the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in alfalfa leaves. Besides, exogenous Si application enhanced photosynthetic parameters of NaCl-stressed alfalfa seedlings, which was accompanied by the improvement in predawn LWP, level of chlorophyll content, and water use efficiency (WUE). The Si-treated plants enhanced salinity tolerance by limiting Na+ accumulation while maintaining K+ concentration in leaves. It also established K+/Na+ homeostasis by increasing K+/Na+ radio to protect the leaves from Na+ toxicity and thereby maintained higher chlorophyll retention. Simultaneously, Si-treated plants showed higher antioxidant activities and decreased MDA content under NaCl stress. Our study concluded that Si application enhanced salt tolerance of alfalfa through improving the leaves photosynthesis, enhancing antioxidant performance and maintaining K+/Na+ homeostasis in leaves. Our data further indicated exogenous Si application could be effectively manipulated for improving salt resistance of alfalfa grown in saline soil.

Maximum elongation growth promoted as a shade-avoidance response by blue light is related to deactivated phytochrome: a comparison with red light in four microgreen species

To clarify detailed patterns of responses to blue light associated with decreasing phytochrome activity, the growth and morphology traits of arugula, cabbage, mustard, and kale microgreens were compared under the treatments: (1) R, pure red light; (2) B, pure blue light; (3) BRF0, (4) BRF2, (5) BRF4, and (6) BRF6: unpure blue lights created by mixing B with low-level (6%) R, and further adding 0, 2, 4, and 6 μmol m−2 s−1 of far-red light, respectively. The calculated phytochrome photostationary state (PPS) value, indicating phytochrome activity, gradually decreased in the order of R (0.89), BRF0 (0.69), BRF2 (0.65), BRF4 (0.63), BRF6 (0.60), and B (0.50). Generally, the elongation growth (including stem extension rate, hypocotyl length, or petiole length) under blue lights increased with the decreasing PPS values, showing the highest and lowest sensitivity for arugula and mustard, respectively. However, the elongation promoted by blue lights gradually became saturated once the PPS values decreased below 0.60, a level which deactivates phytochrome. Other plant traits, such as biomass allocation and plant color, varied with increasing shade-avoidance responses to blue lights with decreasing PPS values relative to R, and these traits reached saturation at a similar PPS value as elongation. The response sensitivity was highest in elongation growth for arugula and cabbage, and highest in plant color for kale and mustard. This suggests that deactivated phytochrome contributes to the maximum elongation promotion as a shade-avoidance response induced by blue light, although the response sensitivity varies with plant traits and species.

Blue versus Red Light Can Promote Elongation Growth Independent of Photoperiod: A Study in Four Brassica Microgreens Species

An elongated stem has beneficial effects on microgreen production. Previous studies indicate that under 24-hour light-emitting diode (LED) lighting, monochromatic blue light, compared with red light, can promote plant elongation for some species. The objective of this study was to investigate whether shortened photoperiod can change blue vs. red light effects on elongation growth. The growth and morphology traits of arugula (Brassica eruca, ‘Rocket’), cabbage (Brassica oleracea, unknown variety name), mustard (Brassica juncea, ‘Ruby Streaks’), and kale (Brassica napus, ‘Red Russian’) seedlings were compared during the stage from seeding to cotyledon unfolding under two light quality × two photoperiod treatments: 1) R, monochromatic red light (665 nm) and 2) B, monochromatic blue light (440 nm) using continuous (24-hour light/0-hour dark) or periodic (16-hour light/8-hour dark) LED lighting. A photosynthetic photon flux density of ≈100 μmol·m−2·s−1 and an air temperature of ≈22 °C was used for the preceding treatments. After 7 to 8 days of lighting treatment, regardless of photoperiod, B promoted elongation growth compared with R, as demonstrated by a greater stem extension rate, hypocotyl length, or petiole length in the tested microgreen species, except for mustard. The promotion effects on elongation were greater under 24- vs. 16-hour lighting in many cases. Among the tested species, mustard showed the lowest sensitivity in elongation response to B vs. R, which was independent of photoperiod. This suggests that the blue-light-promoted elongation is not specifically from 24-hour lighting, despite the varying promotion degree under different photoperiods or for different species. The elongation growth promoted by blue LED light under a photoperiod of either 24 hours or 16 hours can potentially benefit indoor production of microgreens.

Pure blue light effects on growth and morphology are slightly changed by adding low-level UVA or far-red light: A comparison with red light in four microgreen species

To explore the action mode of blue light on elongation growth of microgreens, the growth and morphology traits of arugula (Brassica eruca L., ‘Rocket’), cabbage (Brassica oleracea, unknown variety name), mustard (Brassica juncea, ‘Ruby Streaks’), and kale (Brassica napus, ‘Red Russian’) seedlings were compared under four light quality treatments: (1) R, “pure” red light (660 nm); (2) B, “pure” blue light (450 nm); (3) BU, “unpure” blue light created by mixing B with a low level of UVA (≈7.5% photosynthetic photon flux); and (4) BF, “unpure” blue light created by mixing B with a low level of far-red light (≈ 10% photosynthetic photon flux). Continuous (24-hour) light-emitting diode lighting with either 100 or 50 μmol m−2·s−1 photosynthetic photon flux density at ≈ 23 ℃ was used with the above treatments. After 11 to 14 days of light treatment, B vs. R promoted elongation growth as demonstrated by a greater stem extension rate, hypocotyl length, or petiole length in the tested microgreen species, except for mustard. The promotion effects on elongation were stronger under lower vs. higher light for cabbage and kale, and cotyledon size was also reduced by B vs. R light in most cases, which suggested that stem elongation under pure blue light appeared to be one of the shade-avoidance responses in de-etiolated seedlings. BU vs. B inhibited elongation growth for some species at 100 μmol m−2·s−1 in most cases, but BU vs. R did not, except for mustard at 50 μmol m−2·s−1. BF vs. B increased stem extension rate, and hypocotyl length for arugula and mustard, and petiole length for arugula, but not in other cases. If considering all plant traits together using principle component analysis, BU and BF effects were similar to B, but different from R. This suggests that after adding UVA or far-red light, the pure blue light effects on growth and morphology are slightly changed, with varying sensitivity among species.

Blue light associated with low phytochrome activity can promote elongation growth as shade-avoidance response: A comparison with red light in four bedding plant species

To explore the action mode of blue light on elongation growth of bedding plants, the plant growth and morphology traits of petunia (Petunia × hybrida, ‘Duvet Red’), calibrachoa (Calibrachoa × hybrida, ‘Kabloom Deep Blue’), geranium (Pelargonium × hortorum, ‘Pinto Premium Salmon’), and marigold (Tagetes erecta, ‘Antigua Orange’) were compared under four light quality treatments: (1) R, “pure” red light (660 nm); (2) B, “pure” blue light (450 nm); (3) BR, “unpure” blue light created by mixing B with a low level of R to provide B/R ≈ 9; (4) BRF, “unpure” blue light created by adding a low level of far red light to BR with red/far red ≈ 1. Continuous (24-h) light-emitting diode lighting with either 100 or 50 μmol m−2 s−1 photosynthetic photon flux density at ≈ 23℃ was used with the above treatments. After 14–20 day of lighting treatment, B promoted elongation growth compared to R, as demonstrated by a greater canopy height, main stem length, internode length, and daily main stem extension rate. However, BR showed similar or inhibitory effects on these traits relative to R, while BRF exhibited similar promotion effects as B. The calculated phytochrome photoequilibrium, an indication of phytochrome activity, was higher for R (0.89) and BR (0.74) than for B (0.49) and BRF (0.63). Adding red (or far red) light reversed the effects of B (or BR) on elongation growth and the phytochrome photoequilibrium, suggesting that blue light promotion of elongation growth is related to the lower phytochrome activity. Also, B and BRF, when compared to R or BR, promoted elongation growth to a greater degree at 50 than 100 μmol m−2 s−1 for petunia and calibrachoa. In addition to the promoted elongation growth, B and BRF reduced side branch number, biomass allocation to side branches, leaf epinasty, leaf angle, and/or leaf chlorophyll content relative to R or BR, but increased individual leaf area, petiole length, and/or biomass allocation to main stem, which varied with different species. It suggests that the promoted elongation growth by blue light associated with lower phytochrome activity is one of shade-avoidance responses with varying sensitivity among species.

Carbon limitation, stem growth rate and the biomechanical cause of Corner's rules.

Corner's rules describe a global spectrum from large-leaved plants with thick, sparingly branched twigs with low-density stem tissues and thick piths to plants with thin, highly branched stems with high-density stem tissues and thin piths. The hypothesis was tested that, if similar crown areas fix similar amounts of carbon regardless of leaf size, then large-leaved species, with their distantly spaced leaves, require higher stem growth rates, lower stem tissue densities and stiffnesses, and therefore thicker twigs. Structural equation models were used to test the compatibility of this hypothesis with a dataset on leaf size, shoot tip spacing, stem growth rate and dimensions, and tissue density and mechanics, sampling 55 species drawn from across the angiosperm phylogeny from a morphologically diverse dry tropical community. Very good fit of structural equation models showed that the causal model is highly congruent with the data. Given similar amounts of carbon to allocate to stem growth, larger-leaved species require greater leaf spacing and therefore greater stem extension rates and longer stems, in turn requiring lower-density, more flexible, stem tissues than small-leaved species. A given stem can have high resistance to bending because it is thick (has high second moment of area I) or because its tissues are stiff (high Young's modulus E), the so-called E-I trade-off. Because of the E-I trade-off, large-leaved species have fast stem growth rates, low stem tissue density and tissue stiffness, and thick twigs with wide piths and thick bark. The agreement between hypothesis and data in structural equation analyses strongly suggests that Corner's rules emerge as the result of selection favouring the avoidance of self-shading in the context of broadly similar rates of carbon fixation per unit crown area across species.

Response of growth, yield, and quality of pea shoots to supplemental light-emitting diode lighting during winter greenhouse production

Low natural light levels during the winter months are a major limiting factor for greenhouse production in northern regions. To determine the effects of supplemental lighting (SL) on winter greenhouse production of pea shoots, crop growth, yield, and quality were investigated under the treatments of supplemental photosynthetic photon flux density (PPFD) of 50, 80, 110, and 140 μmol m−2 s−1, all with a 16 h photoperiod, plus a no-SL control treatment, inside a Canadian greenhouse from December to March. Light-emitting diodes with a red to blue PPFD ratio of 4:1 and peak wavelengths at 665 and 440 nm were used for the lighting treatment. During the trial period, the average natural daily light integral (DLI) inside the greenhouse was 5.3 mol m−2 d−1 and the average daily temperature was around 13 °C. Compared with the no-SL control, SL of 50–140 μmol m−2 s−1 increased stem length and leaf number before the first harvest and promoted the cumulative yield (kg m−2) of pea shoots throughout the five harvest times. The total yield (kg m−2) of five harvests and weekly average stem extension rate were proportional to supplemental PPFD within the range of 0–140 μmol m−2 s−1; however, SL of 50–80 μmol m−2 s−1, corresponding to total (natural + supplemental) DLI of 8.1–9.8 mol m−2 d−1, resulted in the best integrated quality based on the evaluation of individual fresh mass, soluble solids content, succulence, and firmness. Therefore, a total DLI ranging between 8.1 and 9.8 mol m−2 d−1 can be suggested as a target for winter greenhouse production of pea shoots under conditions similar to this trial.

Seedling Establishment, Biomass Yield and Water use Efficiencies of Four Maize Varieties as Influenced by Water Deficit Stress

AbstractWater stress is one of the major abiotic factors affecting crop growth and development at every growth stages. Effects of water deficit on the vegetative growth stage of four maize varieties consisting of two Quality Protein Maize varieties (ILE1OB and ART98SW6OB) and two drought tolerant checks (TZPBSR and DTESTRSYN) were evaluated under the screen house conditions at the Institute of Agricultural Research and Training (I.A.R & T), Moor Plantation, Ibadan. Maize seeds were sown in 20 L plastic pots filled with 15 kg top soil, which were subjected to four watering regimes of 25, 50, 75 and 100% field capacities (FC). The experimental design was a 4 × 4 factorial fitted into CRD with four replications. Data were collected on days to germination, number of leaves per plant, leaf area, plant height, stem diameter, leaf extension rate, biomass yield and water use efficiency. The result showed that days to germination were prolonged as the moisture availability decreases, while water use efficiency increased as the moisture level reduced. Reduction in moisture availability caused significant reduction in the other evaluated parameters. At 25% FC DTESTRSYN was superior in leaf area, number of leaves per plant, days to germination and water use efficiency, TZPBSR had highest values for stem diameter and biomass yield, while ILE1OB was superior in plant height, stem diameter, leaf and stem extension rate. ILE1OB competes favourably with the drought tolerant checks and performed better than ART98SW6OB. Adequate moisture condition is fundamental for normal growth and development in maize crops.

Effects of heterogeneous salinity on growth, water uptake, and tissue ion concentrations of alfalfa

Soil salinity varies greatly in the plant rhizosphere. The effect of nonuniform salinity on the growth and physiology response of alfalfa plants was determined to improve understanding of salt stress tolerance mechanisms of alfalfa. Plant growth, predawn leaf water potential, water uptake, and tissue ionic content were studied in alfalfa plants grown hydroponically for 9 days using a split-root system, with uniform salinity or horizontally nonuniform salinity treatments (0/S, 75/S, and 150/S corresponding to 0, 75, and 150 mM NaCl on the low salt side, respectively). Compared with uniform high salinity, 0/S and 75/S treatments significantly increased the alfalfa shoot dry mass and stem extension rate. Compensatory water uptake by low salt roots of 0/S and 75/S treatments was observed. However, decreased leaf Na+ concentration, increased leaf K+/Na+, and compensatory growth of roots on the low salt side were observed only following the 0/S treatment. Nonuniform salinity dose not enhance plant growth once a threshold NaCl concentration in low salinity growth medium has been reached. Compensation of water uptake from the low-salt root zone and regulation of K+/Na+ homeostasis in low salt root play more important role than regulation of leaf ions in enhancing alfalfa growth under nonuniform salinity.

Proximal NDVI derived phenology improves in-season predictions of wheat quantity and quality

Automated, low-cost and field-deployable remote sensing tools are well suited for continuously monitoring crop growth and providing growers with timely information about crop performance. Because automated sensors provide information about crop development and performance across time, we examined the hypothesis that ground-based canopy reflectance data might define crop phenology in new ways over the course of the season that can better forecast crop yield, protein, biomass, and grain nitrogen at harvest. This study examines the utility of daily Normalized Difference Vegetation Index (NDVI) data to monitor crop phenology over two complete growing seasons. Spectral reflectance data was collected at a total of sixteen plots under four different applied nitrogen (N) and soil water availability scenarios in rainfed soft white spring wheat (Triticum aestivum L.). Using NDVI at solar noon, four phenological periods were derived from the data using a non-parametric regression locally weighted smoothing parameter (loess) to account for day to day variability, and piecewise linear regression to determine inflection points in the seasonal NDVI curve. The NDVI derived phenological metrics (i.e. the change in NDVI per day, and duration (in days) of each phenological period) were compared against daily NDVI values throughout the season to predict harvest metrics. Daily NDVI data were generally poor predictors of harvest metrics early in the growing season, and reached maximum predictive power at the onset of heading, and the middle of ripening for biomass and yield (R2∼0.50 and ∼0.25 during heading, respectively, and R2∼0.50 during early ripening). Conversely, using both simple and multiple regression analysis, we found that harvest metrics were better explained using the rate and duration of NDVI derived phenological periods. Simple regressions between NDVI derived phenological metrics revealed several physiologically and management relevant correlations including strong, statistically significant (p<0.05) relationships between the rate of tillering and stem extension and total biomass (R2=0.63 and 0.54, respectively), the duration of heading and yield (R2=0.67), the rate of ripening and grain protein concentration (R2=0.45), and the duration of ripening and grain N content (R2=0.43), for example. Using multiple regression analysis, 83% of the variance in yield, 67% in protein concentration, 87% in total biomass, and 80% in grain N was explained by two to three NDVI derived phenological metrics. Further, multiple regression analysis using NDVI derived phenological metrics from the early season (tillering and stem extension) substantially improved early prediction of yield and biomass as compared to daily NDVI data, whereas protein and grain N were primarily driven by metrics associated with the reproductive development of the crop (heading and ripening). This work has implications for improving in-season management decisions and understanding of the phenological drivers of harvest metrics using daily NDVI data as an evaluation tool.

Immunoprofiling reveals unique cell‐specific patterns of wall epitopes in the expanding Arabidopsis stem

The Arabidopsis inflorescence stem undergoes rapid directional growth, requiring massive axial cell-wall extension in all its tissues, but, at maturity, these tissues are composed of cell types that exhibit markedly different cell-wall structures. It is not clear whether the cell-wall compositions of these cell types diverge rapidly following axial growth cessation, or whether compositional divergence occurs at earlier stages in differentiation, despite the common requirement for cell-wall extensibility. To examine this question, seven cell types were assayed for the abundance and distribution of 18 major cell-wall glycan classes at three developmental stages along the developing inflorescence stem, using a high-throughput immunolabelling strategy. These stages represent a phase of juvenile growth, a phase displaying the maximum rate of stem extension, and a phase in which extension growth is ceasing. The immunolabelling patterns detected demonstrate that the cell-wall composition of most stem tissues undergoes pronounced changes both during and after rapid extension growth. Hierarchical clustering of the immunolabelling signals identified cell-specific binding patterns for some antibodies, including a sub-group of arabinogalactan side chain-directed antibodies whose epitope targets are specifically associated with the inter-fascicular fibre region during the rapid cell expansion phase. The data reveal dynamic, cell type-specific changes in cell-wall chemistry across diverse cell types during cell-wall expansion and maturation in the Arabidopsis inflorescence stem, and highlight the paradox between this structural diversity and the uniform anisotropic cell expansion taking place across all tissues during stem growth.

Early growth responses of mangroves to different rates of nitrogen and phosphorus supply

Experiments were conducted in an outdoor facility to quantify growth responses of six mangrove species to rates of dissolved inorganic nitrogen and phosphorus supply mimicking the range of N and P mineralization rates in natural soils. Growth of all six species on nitrogen was nonlinear. Stem extension rates of Rhizophora apiculata and Xylocarpus granatum were enhanced to the highest rate of N supply (50 mmol m − 2 d − 1 ); Bruguiera gymnorrhiza, Avicennia marina, and Xylocarpus moluccensis stem growth leveled off by 10 mmol m − 2 d − 1 . Stem growth of Ceriops tagal peaked at 24–26 mmol N m − 2 d − 1 . Except for A. marina and C. tagal, rates of biomass increase declined at the highest supply rate, indicating NH 4 + toxicity. At different rates of P supply, stem extension rates and rates of biomass increase of R. apiculata and C. tagal best-fit Gaussian curves and B. gymnorrhiza stem growth and biomass increase best-fit sigmoidal and Gaussian curves, respectively; X. moluccensis stem and biomass growth increased linearly, but stem and biomass growth rates of A. marina did not vary in relation to P supply. Stem growth of X. granatum was Gaussian but rates of biomass increase best-fit a quadratic equation. Changes in leaf and root N and P content mirrored the growth responses. As rates of N and P mineralization in natural mangrove soils overlap with the lowest rates of N and P supplied in these experiments, the growth responses imply that mangroves are intrinsically nutrient-limited at mineralization rates often encountered in nature. Such species specificity may have significant implications for recruitment success and the establishment of species gradients within mangrove forests.

Dissolved iron supply limits early growth of estuarine mangroves

Three mesocosm experiments were performed in an outdoor facility to quantify the responses of five mangrove species grown from seedling to sapling stage to increasing rates of dissolved iron supply. Stem extension and biomass of mangroves were measured in the first two experiments, and in the third experiment, rates of microbial iron reduction were measured in relation to stem extension of two mangrove species. In all experiments, mangrove growth was enhanced by increasing iron supply, although some species showed iron toxicity at the higher supply rates. In the first two experiments, stem extension rates of Rhizophora apiculata, Bruguiera gymnorrhiza, and Xylocarpus moluccensis best fit Gaussian curves with maximal growth at supply rates of 50-60 mmol Fe x m(-2) x d(-1), whereas growth of Avicennia marina and Ceriops tagal increased to the highest rate (100 mmol Fe x m(-2) x d(-1)) of iron supply. Changes in leaf chlorophyll concentrations and iron content of roots mirrored the growth responses. In the third experiment, rates of microbial iron reduction were greater with R. apiculata and A. marina than in controls without plants; for both species, there was a positive relationship between stem extension and iron reduction. The rates of iron reduction and rates of iron supplied to the plants were well within the range of interstitial iron concentrations and rates of iron reduction found in the natural mangrove soils from which the seedlings were obtained. The responses of these species show that mangroves growing from seedling to sapling stage have a strong nutritional requirement for iron, and that there is a close relationship between plant roots and the activities of iron-reducing bacteria. These results suggest that mangrove growth may be limited in some natural forests by the rate at which iron is solubilized by iron-reducing bacteria. Such biogeochemical conditions have significant implications for successful recruitment, establishment, and early growth of mangroves.

Gas exchange and plant growth after defoliation on Leandra lacunosa, a cerrado woody species with continuous leaf production

Morphological and physiological leaf traits were studied on control and defoliated potted Leandra lacunosa young plants. After defoliation, remaining bottom leaves showed no significant change in net photosynthesis and stomatal conductance values with time, but the leaf transpiration rate was higher. The production of the new leaves was greater after defoliation in top defoliated plants. Bottom defoliated plants increased stem extension rates and net photosynthesis transitorily. Two months after defoliation, control and defoliated plants did not differ in stem length and root dry mass values. In spite of smaller area and photosynthetic capacity, remaining bottom leaves were able to compensate top leaves elimination. The effectiveness of this compensatory response, however, depended on the ability of new leaves to escape from herbivores.

Daily shoot extension growth of peach trees growing on rootstocks that reduce scion growth is related to daily dynamics of stem water potential.

We studied relationships between diurnal patterns of stem water potential (PsiSTEM) and stem extension growth of the same scion cultivar growing on three rootstocks with differing size-controlling potentials. The peach trees (Prunus persica (L.) Batsch) used in this field experiment consisted of an early-maturing freestone cultivar, 'Flavorcrest,' grafted onto three different rootstocks: Nemaguard (a vigorous seed-propagated control, P. persica x P. davidiana hybrid), Hiawatha (an intermediate vigor rootstock, derived from an open pollinated seedling of a P. besseyi x P. salicina hybrid) and K-146-43 (a semi-dwarfing rootstock, P. salicina x P. persica hybrid). Diurnal patterns of PsiSTEM and stem extension growth were measured on six dates (March 29, April 12, April 26, May 10, May 24 and June 18) during the primary period of peach shoot extension growth. Rootstocks clearly affected diurnal patterns of PsiSTEM and stem extension growth. Trees on K-146-43 had the lowest midday PsiSTEM and stem extension growth. Differences among rootstocks in the amount of diurnal oscillation in PsiSTEM explained stem extension rate differences induced by the three rootstocks. The sensitivity of shoot extension growth to tree water relations tended to decrease as the season progressed and was not apparent by mid-June. The results of the study indicate that water relations may play an important role in the dwarfing mechanism induced by size-controlling peach rootstocks.

Growth and reproductive characteristics of the columnar cactus Stenocereus queretaroensis and their relationships with environmental factors and colonization by arbuscular mycorrhizae.

Three natural populations of pitayo (Stenocereus queretaroensis (Weber) Buxbaum), a columnar arborescent cactus, were studied in their subtropical environments in western Mexico. All of the sites were characterized by shallow, nutrient-poor soils. Percentage of colonization by arbuscular mycorrhizae (AM) fungi, stem growth, fruit mass, and percentage germination were greater in S. queretaroensis at Autlan, Jalisco (AJ) than at Zacoalco de Torres, Jalisco (ZTJ) or Santa Rosa, Zacatecas (SRZ). The onset of root colonization by arbuscular mycorrhizae during the middle of the summer wet period preceded increases in stem extension rate and stem phosphorus concentration. Based on previous studies of effects of environmental factors on photosynthesis, climatic conditions were more favorable for photosynthesis at AJ than at SRZ and ZTJ, as indicated by the amount of summer rainfall, the amount of light, and the moderate air temperatures that prevailed during the fall and winter seasons. There was a significant positive correlation between stem growth and percentage of total root length colonized by arbuscules of AM fungi for S. queretaroensis at SRZ and AJ, but not at ZTJ. A negative significant correlation was observed between stem growth and maximal and minimal air temperatures at the three study sites. Stem growth was positively related to rainfall only at SRZ, and light was statistically related to stem growth only at ZTJ. Among sites, S. queretaroensis at AJ had the highest carbon gain and greatest AM colonization, creating physiological conditions that led to the highest stem growth, fruit mass and percentage of seed germination.

Effect of intercropping maize and solanum potato on yield of the component crops in Central Uganda

Three potato (Solunum tuberosum) varieties and one maize variety were intercropped in six spatial arrangements, viz., sole crops, 2:1, 2:2, 1:1, 1:2 potato: maize row arrangements and one additive mixture. Intercropping influenced some growth parameters of potato but not of maize. For instance, the rate of potato stem extension and leaf formation rates were hastened by intercropping. Branching in potato influenced leaf area development, especially during the second season when the additive mixture supported the least leaf area. Potato yield differed significantly among the spatial arrangements with the highest yield in the sole crop followed closely by the 2:1 and 2:2 potato: maize mixtures. However, these yield differences depended on potato variety, with Kisoro being the most responsive to changes in spatial arrangement. Assessment of biological efficiency of intercropping using the Land Equivalent Ratio (LER) method, revealed that yield advantages increased slightly with increase in the proportion of potato in the mixtures. However, it was only the additive mixture with a significant overall LER of 1.58, indicating a 58.2% yield advantage for intercropping. The contribution of maize to total LER was greatest in the 1:2 and additive mixtures. Key Words: Biological efficiency, inter-cropping, land equivalent ratio, Solanum tuberosum, spatial arrangement, yield advantage (African Crop Science Journal 2001 9(1): 83-96)

Does far-red light affect growth and mycorrhizas of Scots pine seedlings grown in forest soil?

We studied the response of Scots pine (Pinus sylvestris L.) to supplementary far-red sidelight in seedlings grown in a forest soil substrate without additional nutrient supply. Our aim was to determine possible changes in the accumulation and allocation of dry weight and mineral nutrients and the presence of mycorrhizas. Half of the seedlings were grown in light conditions simulating reflected far-red light (FR) from neighbouring plants and the other half were controls not receiving additional FR. PAR irradiance was kept constant in both treatments. At the first harvest (41 d of treatment), FR+ had no effect on stem height, biomass accumulation or allocation. However, at the end of the experiment (93 d of treatment), an increase in stem extension rate and stem dry weight was observed in FR+ seedlings when compared to controls. Both control and treated plants had several morphological types of ectomycorrhizas, but no effect of FR+ on the frequency of these morphotypes was observed. Nor was the concentration of ergosterol or estimated mycorrhizal fungal biomass affected. Nutrients were more responsive to the light quality treatment: P concentration in roots and N and P contents in stems and roots were higher in FR+ plants than in control seedlings. These results are in contrast to those of a previous study in which the root system of pine seedlings, which were fertilised and had less developed mycorrhizas, was reduced by FR+.

Early signals in field grown wheat in response to shallow soil drying

The aim of the present work was to test under field condition earlier climate room findings that root-borne signals may control stomatal closure and leaf extension rate during mild soil drying. Stomatal conductance (g H2O) of flag leaves, leaf and stem extension rates, leaf water relations, leaf ABA content and predawn xylem [ABA] were measured daily in wheat grown in two soil types (sand and loam) in lysimeters in the field during a period of soil drying with high and low evaporative demands. At 3 days after withholding irrigation (DAI) on both soil types, when soil water potential (Ψsoil) in the upper soil profile of the droughted treatment had dropped to –70 kPa and with the lower layers still at field capacity, predawn xylem [ABA] increased. At 4 DAI the leaf extension rate decreased and midday leaf ABA content increased. Stem extension rates decreased at 5 DAI in loam and 7 DAI in sand. g H2O started to decrease 6 DAI in loam and 9 DAI in sand. These responses were observed before any detectable decrease in the midday leaf water status of the droughted plants had occurred relative to well- watered plants. The responses were closely related to Ψsoil and independent of evaporative demand. We conclude that, in wheat, root-borne signals probably control stomatal conductance and leaf extension rate during mild soil drying in the field.