Growth Of Mature Plants Research Articles

Ultraviolet A and Blue Light Transiently Regulate Total Phenolic and Anthocyanin Concentrations in Indoor-grown Red-leaf Lettuce

In controlled environments, supplementing a light spectrum with ultraviolet A (UVA; 315–399 nm) or blue (B; 400–499 nm) light increases the concentrations of phenolic compounds that can increase quality attributes, such as leaf pigmentation and nutritional quality of lettuce (Lactuca sativa). However, B light and sometimes UVA light can inhibit leaf expansion and biomass accumulation when continuously applied, whereas applying it only at the end of the production cycle can increase lettuce quality with little to no effect on crop yield. Our objective was to quantify the persistency of periodic supplemental UVA or B light and compare end-of-production with continuously applied supplemental light during indoor lettuce production on quality attributes and biomass accumulation. We hypothesized that supplemental UVA or B light would be more effective later, rather than earlier, during production with increasing lettuce quality attributes. We grew ‘Rouxai’ red-leaf lettuce hydroponically at an air temperature of 23 °C under 75 μmol⋅m−2⋅s−1 of red (peak = 664 nm) plus 75 μmol⋅m−2⋅s−1 of warm-white light provided by light-emitting diodes. The supplemental lighting treatments consisted of adding 30 μmol⋅m−2⋅s−1 of UVA (peak= 386 nm) or B (peak = 449 nm) light during the seedling phase (P1; days 4–12), growth phase (P2; days 12–20), finishing phase (P3; days 20–28), or the entire time (ET; days 4–28). Supplemental UVA or B light applied at any individual phase did not inhibit biomass accumulation, whereas enriched B light during the entire production period inhibited fresh mass compared with no supplemental light. Additionally, supplemental UVA or B light during P3 or ET similarly increased total phenolic and anthocyanin concentrations. Finally, applying UVA or B light during P1 or P2 had no residual effect on mature plant growth or quality at harvest. We concluded that the end of the production cycle is the optimal time to apply supplemental UVA or B light to improve lettuce coloration and phenolic content, that earlier application elicits transient responses, and that continuous application improves lettuce quality but inhibits biomass accumulation. Finally, there are potential energy savings by using end-of-production supplemental light compared with continuous application of the same spectrum.

Soybean and Cotton Spermosphere Soil Microbiome Shows Dominance of Soilborne Copiotrophs.

The spermosphere is the transient, immediate zone of soil around imbibing and germinating seeds. It represents a habitat where there is contact between seed-associated microbes and soil microbes, but it is studied less than other plant habitats. Previous studies on spermosphere microbiology were primarily culture based or did not sample the spermosphere soil as initially defined in space and time. Thus, the objectives of this study were to develop an efficient strategy to collect spermosphere soils around imbibing soybean and cotton in nonsterile soil and investigate changes in microbial communities. The method employed sufficiently collected spermosphere soil as initially defined in space by constraining the soil sampled with a cork borer and confining the soil to a 12-well microtiter plate. Spermosphere prokaryote composition changed over time and depended on the crop within 6 h after seeds were sown. By 12 to 18 h, crops had unique microbial communities in spermosphere soils. Prokaryote evenness dropped following seed imbibition, with the proliferation of copiotrophic soil bacteria. Due to their long history of plant growth promotion, prokaryote operational taxonomic units (OTUs) in Bacillus, Paenibacillus, Burkholderia, Massilia, Azospirillum, and Pseudomonas were notable organisms enriched. Fungi and prokaryotes were hub taxa in cotton and soybean spermosphere networks. Additionally, the enriched taxa were not hubs in networks, suggesting that other taxa besides those enriched may be important for spermosphere communities. Overall, this study advances knowledge in the assembly of the plant microbiome early in a plant's life, which may have plant health implications in more mature plant growth stages. IMPORTANCE The central hypothesis of this research was that plant species and seed exudate release would alter the assembly of microbes in the spermosphere soil. Our research investigated the response of microbes to the initial burst of nutrients into the spermosphere soil, filling knowledge gaps from previous studies that pregerminated seeds under sterile conditions. We identified several copiotrophic bacterial lineages with a long history of plant growth promotion proliferating in response to the initial exudate release. With a comparative network approach, we show that these copiotrophic bacteria are not central to networks, demonstrating that other microbes (including fungi) may be important for community structure. This study improves knowledge on microbial dynamics in the understudied spermosphere and helps inform solutions for biologically or ecologically motivated solutions to spermosphere pathogens.

The Arabidopsis SAFEGUARD1 suppresses singlet oxygen-induced stress responses by protecting grana margins

Singlet oxygen (1O2), the major reactive oxygen species (ROS) produced in chloroplasts, has been demonstrated recently to be a highly versatile signal that induces various stress responses. In the fluorescent (flu) mutant, its release causes seedling lethality and inhibits mature plant growth. However, these drastic phenotypes are suppressed when EXECUTER1 (EX1) is absent in the flu ex1 double mutant. We identified SAFEGUARD1 (SAFE1) in a screen of ethyl methanesulfonate (EMS) mutagenized flu ex1 plants for suppressor mutants with a flu-like phenotype. In flu ex1 safe1, all 1O2-induced responses, including transcriptional rewiring of nuclear gene expression, return to levels, such as, or even higher than, those in flu Without SAFE1, grana margins (GMs) of chloroplast thylakoids (Thys) are specifically damaged upon 1O2 generation and associate with plastoglobules (PGs). SAFE1 is localized in the chloroplast stroma, and release of 1O2 induces SAFE1 degradation via chloroplast-originated vesicles. Our paper demonstrates that flu-produced 1O2 triggers an EX1-independent signaling pathway and proves that SAFE1 suppresses this signaling pathway by protecting GMs.

Exploration of Root-associated Bacteria from the Medicinal Plant Platycodon grandiflorum.

The present study was performed to investigate root-associated bacteria from Platycodon grandiflorum, a medicinal plant commonly grown in East Asia. Isolates were obtained from the rhizosphere or root interior with various culture media, and phylogenetic analyses were performed based on their 16S rDNA sequences. In consideration of practical applications, traits related to plant growth promotion and niche adaptation were assessed in several endophytic strains with fewer biosafety concerns. The effects of a bacterial inoculation on seedling and mature plant growth were evaluated. Seventeen genera that encompassed more than 30 bacterial lineages were successfully retrieved from the roots, the majority of which have not been reported as P. grandiflorum-associated bacteria, particularly for non-negligible Proteobacteria. Although nitrogen-fixing or phosphate-solubilizing and indole acetic acid-producing activities were recorded in all of the strains selected, these strains were beneficial or detrimental to plant growth as evidenced by their influence on the length of seedlings and biomass of mature plants. Among the 4 endophytic Rhizobium species tested in the present study, the potentially novel Rhizobium sp. BF-E16, which was more compatible with the non-leguminous medicinal plant P. grandiflorum, was identified. Other than plant growth-promoting traits, characteristics such as plant constituent-hydrolyzing activities need to be taken into consideration and their roles clarified when investigating plant growth-promoting rhizobacteria.

Regulatory effects of sulfur on oilseed rape (Brassica napus L.) response to selenite

ABSTRACTSelenite is a form of selenium (Se) commonly found in Se-excessive soils. To regulate the Se content in plants in high-Se areas, a potted soil experiment was performed on oilseed rape (Brassica napus L.) to evaluate the effects of varied amounts of sulfur (S) on the biomass, accumulation and distribution of Se in B. napus under the conditions of different amounts of Se in the soil. The results showed that the seedlings of B. napus were more sensitive to Se than the mature plants were. The addition of S significantly alleviated the growth inhibition in seedlings and facilitated the growth of mature plants under higher Se (15 mg kg−1) conditions. S treatment significantly decreased soil pH within the range of 0.22–0.60. An appropriate moderate amount (150 mg kg−1) of S exerted the strongest inhibition on Se concentration and accumulation in B. napus at the seedling stage, but a higher amount (300 mg kg−1) of S led to a more significant decrease in the mature plants under higher Se conditions, with the maximum reduction in various parts of B. napus reaching 51.3–60.9% and 42.5–53.4%, respectively. The application of S only affected the uptake of Se, and not the translocation of Se; the accumulation of Se in B. napus follows the sequence of pod ≈ stem > rapeseed > root, and the distribution ratio is approximately 1.00:0.97:0.69:0.49. Overall, the application of S alleviated the inhibitory effect on growth caused by excessive Se by reducing the Se concentration in B. napus and facilitating its growth, suggesting that S treatment is a suitable and highly cost-effective method to regulate the content of Se in B. napus.

Overexpression of the MYB37 transcription factor enhances abscisic acid sensitivity, and improves both drought tolerance and seed productivity in Arabidopsis thaliana.

Although a lot of genes have been revealed to participate in abscisic acid (ABA) signaling, many of the additional components involved in ABA signaling remain to be discovered. Here we report that overexpression of MYB37, a R2R3 MYB subgroup 14 transcription factor in Arabidopsis thaliana, confers hypersensitive phenotypes to exogenous ABA in all the major ABA responses, including ABA-induced inhibition of seed germination, cotyledon greening and early seedling growth, and ABA-induced stomatal closure and inhibition of stomatal opening. Interestingly and importantly, MYB37-overexpression improves plant tolerance to drought, enhances growth of mature plants and seed productivity, thought it delays flowering, which suggests that this gene may be used for improving crop adaptability to drought environment and productivity. However, a myb37-1 knockout mutant displays wild-type ABA responses most likely due to a functional redundancy of the multiple MYB members. Real-time PCR analysis shows that upregulation of the MYB37 expression changes expression of a subset of ABA-responsive genes. Together, these findings suggest that the MYB37 transcription factor plays an important, positive role in plant response to ABA and drought stress, and meanwhile, it plays a positive role in the regulation of seed production.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-015-0411-1) contains supplementary material, which is available to authorized users.

Eggplant (Solanum melongena L.) Plant Growth and Fruit Yield as Affected by Drip Irrigation Rate

Eggplant (Solanum melongena L.) is an increasingly popular crop in the United States. In the southeastern United States, eggplant is often produced with high levels of irrigation water [above the rate of crop evapotranspiration (ETc)], resulting in water waste and nitrogen (N) leaching. The objective of this research was to assess the effects of irrigation rate on plant growth and fruit yield in eggplant. The study was conducted in Tifton, GA, in the fall of 2010 and 2011. Eggplant plants cv. Santana were grown on raised beds (1.8 m centers) covered with white plastic film mulch. There was a single drip tape along the center of the bed. The design was a randomized complete block with five treatments and four replications. Treatments consisted of irrigation rates based on ETc (33%, 67%, 100%, 133%, and 167% ETc). Plant growth, chlorophyll index (CI), and volumetric soil water content (SWC) were monitored over the season. In 2010, SWC (0–30 cm deep) increased and soil nitrate levels decreased with increasing irrigation rates. Foliar N and potassium (K), and CI decreased with increasing irrigation rate, probably due to a dilution effect. Stem diameter, leaf dry weight (DW), and vegetative top DW increased with increasing irrigation rate. Net photosynthesis and stomatal conductance (gS) were lowest at 33% ETc. Fruit number and fruit yields (marketable and total) were also lowest at 33% ETc and there were little yield differences among irrigation rates higher than 33% ETc. In 2011, irrigation rate had minor or no effect on SWC, plant growth of mature plants, leaf gas exchange, and fruit number and yield. The no treatment effect observed for eggplant in 2011 was likely because study was conducted in a low field that remained moist most of the time, nullifying the treatment effects. Results suggested that eggplant may tolerate mild water stress, since plants irrigated at 67% ETc produced fruit yields similar to those of plants irrigated at 100% ETc or higher rates. Thus, there is a potential to save water by reducing current irrigation rates without negatively impacting fruit yields.

Weed Management, Training, and Irrigation Practices for Organic Production of Trailing Blackberry: I. Mature Plant Growth and Fruit Production

Weed management, training time, and irrigation practices were evaluated from 2013 to 2014 in a mature field of trailing blackberry (Rubus L. subgenus Rubus Watson) established in western Oregon. The field was planted in 2010 and certified organic in 2012, before the first harvest season. Treatments included two cultivars (Marion and Black Diamond), three weed management practices [nonweeded, hand-weeded or bare soil, and weed mat (black landscape fabric)], two irrigation strategies (irrigation throughout the growing season and no postharvest irrigation), and two primocane training dates (August and February). When averaged over the other treatments, ‘Marion’ and ‘Black Diamond’ had similar yields in both years. However, the presence of weeds reduced vegetative growth and yield, especially in ‘Black Diamond’, while weed mat increased growth and yield over hand-weeded plots by 13%. Withholding irrigation after harvest reduced water use by an average of 44% each year without adversely affecting yield in either cultivar. The effects of training time were primarily seen in 2014 after a cold winter. August-trained ‘Marion’ plants had more cold damage than February-trained plants and, consequently, had fewer and shorter canes, less biomass, fewer nodes, and 1 kg/plant less yield than February-trained plants. ‘Black Diamond’ was cold hardier than ‘Marion’, but was more readily infested by raspberry crown borer (Pennisetia marginata Harris). As the planting reached maturity, yields in the best performing organic production systems (both cultivars under weed mat and ‘Marion’ that was February-trained) averaged 11 and 9 t·ha−1, for ‘Black Diamond’ and ‘Marion’ respectively, similar to what would be expected in conventional production.

Effects of temperature, salinity and seed age on induction of Zostera japonica germination in North America, USA

Seagrasses can colonize unstructured mudflats either through clonal growth or seed germination and survival. Zostera japonica is an introduced seagrass in North America that has rapidly colonized mudflats along the Pacific Coast, leading to active management of the species. Growth and physiology have been evaluated; however, there is little information about the factors influencing seed germination. We examined the effects of storage and induction temperature (10, 15, 20°C) and salinity (0, 10, 20, 30), and storage period (1.5 and 26 months) on germination of seeds of the seagrass Z. japonica collected from Yaquina Bay, Oregon, USA. Seed germination at 15 and 20°C was 1.24 times higher than at 10°C. Cumulative seed germination at salinity 0 during the first 28 days was 6.5 times greater than at a salinity of 10; similarly, initial seed germination at a salinity of 10 was 7.3 times greater than that observed for salinity 20 and 30. The proportion of germinated seeds collected in 2011 and stored for 26 months was 1.24 times greater than seeds collected in 2013 that were stored for only 6 weeks. Overall average germination rates were 21.6% and 17.1% for 2011 and 2013, respectively. Our experimental results indicate that salinity had a much stronger control over Z. japonica germination than temperature, and the long storage period suggests that Z. japonica is capable of developing a persistent seed bank. We hypothesize that Z. japonica uses seasonal variations in temperature and salinity to avoid competition between generations favoring germination under conditions that are not optimal for the growth of mature plants.

Emergence, Forage Production, and Ion Relations of Alfalfa in Response to Saline Waters

ABSTRACTAlfalfa (Medicago sativa L.) is an important crop utilized in irrigated regions that are commonly impacted by salinity. We evaluated the effect of salinity continually from emergence to mature plant growth in successive harvests. We studied emergence, biomass production, salt tolerance, and shoot ion composition as potential physiological mechanisms in four nondormant salt‐tolerant cultivars: Salado, SW 8421S, SW 9720, and SW 9215. Irrigation water salinity dominated by sodium sulfate ranging from 3.1 to 30 dS m−1 of electrical conductivity (ECiw) was imposed at planting date. Plants were grown in outdoor sand tanks in Riverside, CA for 300 d. Relative emergence (%) decreased above ECiw 12.7 dS m−1 and was reduced to 53 and 13.4% at 18.4 and 24 dS m−1, respectively. At ECiw 30 dS m−1 there were no survivor plants. Absolute and relative accumulated biomass from 6 harvests significantly decreased for ECiw above 12.7 dS m−1 (6.0 dS m−1 in the saturation extract [ECe]). Plants grown at 18.4 and 24 dS m−1 produced 68% and 30% respectively of the biomass produced at 3.1 dS m−1. Salado showed the least reduction in biomass at elevated salinity and, as with all the cultivars, exhibited yield increases in successive harvests from first through seventh. Increasing salinity increased shoot Na+, total‐S, Cl−, Mg2+, and P and decreased K+ and Ca2+. The ability of Salado to maintain low shoot Na was the mechanism most associated with salt tolerance. Saline waters with resultant ECe values of up to 6 dS m−1 did not significantly reduce total forage production of the second through the seventh harvests. This suggests that irrigation with saline waters resulting in ECe values less than 6 dS m‐1 can be used throughout the production cycle (planting to multiple harvests) without significant yield loss for the cultivars examined.

Metabolic adaptation to sugar/O2 deficiency for anaerobic germination and seedling growth in rice

Rice is characterized by a broad range of metabolic and morphological adaptations to flooding, such as germination and mobilization of stored nutrients under submergence until seedlings reach the water surface to carry out photosynthesis, and sustainable growth of mature plants for long durations under partial submergence. The underlying mechanisms of the molecular basis of adaptation to anaerobic germination and seedling growth in rice are being uncovered. Induction of an ensemble of hydrolases to mobilize endosperm nutrient reserves is one of the key factors for successful germination and coleoptile elongation in rice under submergence. To compensate for reduced efficiency of Tricarboxylic Acid cycle and oxidative respiration in mitochondria under O2 deficient conditions, α-amylases play a central role in the hydrolysis of starch to provide sugar substrates for glycolysis and alcohol fermentation for generating ATP. We review the progress on the molecular mechanism regulating α-amylase expression that involves the integration of signals generated by the hormone gibberellin (GA), sugar starvation and O2 deprivation that results in germination and sustainable seedling growth in rice under anaerobic conditions. Comparisons are also made between dicots and monocots for the molecular mechanism of induction of genes involved in alcohol fermentation and sugar/O2 deficiency sensing system.

Biological control of anthracnose of chilli with rhizosphere and rhizoplane fungal isolates from grasses

The fungal species from rhizosphere and rhizoplane of perennial grasses of the Western Ghats of India were studied for their pathogenicity, antagonism in vitro, substrate and root colonization abilities, rhizosphere competence, growth in different soil pH and inoculum shelf-life. Out of 138 non-pathogenic fungal isolates tested, 85 were antagonistic in vitro to chilli anthracnose pathogen Colletotrichum capsici. Fifteen isolates with >60% inhibition zone to pathogen culture had saprophytic and root and rhizosphere colonization abilities. The sorghum grain inocula of test antagonistic fungi- Fusarium oxysporum, Chaetomium globosum and Trichoderma harzianum had the shelf-life of 90 days at 20 ± 2 °C and required optimum soil pH of 6.5. The above fungal isolates when tested for biocontrol of anthracnose disease in greenhouse and field caused reduction in seedling mortality and decreased disease incidence and severity at various plant growth stages and significant reduction in chilli fruit and seed infection. The test antagonistic fungi promoted seedling and mature plant growth and increased fruit and seed yield. Populations of these antagonistic fungi were fairly high in chilli rhizosphere at harvest. The present study indicated that antagonistic fungi from grass rhizosphere and rhizoplane could be used to control anthracnose and promote plant growth, and increase yield of chilli in field.

OSCILLATOR: A system for analysis of diurnal leaf growth using infrared photography combined with wavelet transformation

BackgroundQuantification of leaf movement is an important tool for characterising the effects of environmental signals and the circadian clock on plant development. Analysis of leaf movement is currently restricted by the attachment of sensors to the plant or dependent upon visible light for time-lapse photography. The study of leaf growth movement rhythms in mature plants under biological relevant conditions, e.g. diurnal light and dark conditions, is therefore problematic.ResultsHere we present OSCILLATOR, an affordable system for the analysis of rhythmic leaf growth movement in mature plants. The system contains three modules: (1) Infrared time-lapse imaging of growing mature plants (2) measurement of projected distances between leaf tip and plant apex (leaf tip tracking growth-curves) and (3) extraction of phase, period and amplitude of leaf growth oscillations using wavelet analysis. A proof-of-principle is provided by characterising parameters of rhythmic leaf growth movement of different Arabidopsis thaliana accessions as well as of Petunia hybrida and Solanum lycopersicum plants under diurnal conditions. The amplitude of leaf oscillations correlated to published data on leaf angles, while amplitude and leaf length did not correlate, suggesting a distinct leaf growth profile for each accession. Arabidopsis mutant accession Landsberg erecta displayed a late phase (timing of peak oscillation) compared to other accessions and this trait appears unrelated to the ERECTA locus.ConclusionsOSCILLATOR is a low cost and easy to implement system that can accurately and reproducibly quantify rhythmic growth of mature plants for different species under diurnal light/dark cycling.

TISSUE ELEMENT CONCENTRATIONS AND MINERAL REMOVAL RATES IN HONEYBUSH TEA I: CYCLOPIA GENISTOIDES

Results from a five year survey of honeybush (Cyclopia genistoides) in the Cape Floral Kingdom, South Africa, showed that concentrations of nitrogen, phosphorus, potassium, calcium and magnesium in the top growth of mature plants grown from seedlings were 1.29, 0.05, 0.53, 0.22 and 0.09%, respectively. Removal rates at each harvest were 8.23, 0.32, 3.38, 1.40 and 0.57 g of the respective elements per plant. These quantities were equivalent to 48% to 61% of the total mass of each element in the plant. Concentrations in the top growth of sodium, manganese, iron, copper, zinc and boron were, respectively, 1423, 16, 172, 5, 12 and 23 mg kg−1. Seedlings of C. genistoides reached their peak mass around five years after planting, and attained higher dry masses in plantations than in the open veld. Mature, plantation-grown C. genistoides plants yielded around 638 g of top growth dry mass per plant at each harvest.

Overexpression of Maize IAGLU in Arabidopsis thaliana Alters Plant Growth and Sensitivity to IAA but not IBA and 2,4-D

Overexpression of the IAGLU gene from maize (ZmIAAGLU) in Arabidopsis thaliana, under the control of the CaMV 35S promoter, inhibited root but not hypocotyl growth of seedlings in four different transgenic lines. Although hypocotyl growth of seedlings and inflorescence growth of mature plants was not affected, the leaves of mature plants were smaller and more curled as compared to wild-type and empty vector transformed plants. The rosette diameter in transgenic lines with higher ZmIAGLU expression was also smaller compared to the wild type. Free indole-3-acetic acid (IAA) levels in the transgenic plants were comparable to the wild type, even though a decrease in free IAA levels might be expected from overexpression of an IAA-conjugate–forming enzyme. IAA-glucose levels, however, were increased in transgenic lines compared to the wild type, indicating that the ZmIAGLU gene product is active in these plants. In addition, three different 35SZmIAGLU lines showed less inhibition of root growth when cultivated on increasing concentrations of IAA but not indole-3-butyric acid (IBA) and 2,4-dichlorophenoxyacetic acid (2,4-D). Feeding IAA to transgenic lines resulted in increased IAA-glucose synthesis, whereas the levels of IAA-aspartate and IAA-glutamine formed were reduced compared to the wild type. Our results show that IAA homeostasis can be altered by heterologous overexpression of a conjugate-forming gene from maize.

Seedling development and patch formation of the seagrass Posidonia australis in a southeast Australian estuary

Seedlings of the seagrass Posidonia australis are rarely found and little is known about their development. St. Georges Basin, an estuary in southeast Australia, harbours relatively large numbers of P. australis seedlings and patches. Seedlings of varying age were collected from four sites within the estuary. Mature plagiotropic shoots (horizontal rhizomes) on existing beds were tagged to measure vegetative growth and provide a plastochrone interval with which to age the seedlings. The abundance of P. australis seedlings ranged from 0.001 to 0.014 seedlings m −2. Based on the plastochrone intervals (plagiotropic: 33±0.8 days; orthotropic: 48.0±1.4 days) estimated seedling age ranged from 0.7 to 8.2 years. Both the numbers of shoots and leaf areas were related to seedling age, with increases particularly evident between 2 and 5 years. Of 57 seedlings either collected or observed in situ, only 6 had produced a plagiotropic shoot. Rhizome growth for the seedlings ranged from 5.1±0.5 to 17.1±1.3 cm per year, which was slower than the mean rhizome growth of mature plants (21.4±1.0 cm per year). A development time-line was constructed for P. australis for the first 5 years of seedling growth based on the data collected. On average, production of a second shoot occurred at the age of 2.7±0.3 years, and thereafter approximately one shoot was produced per year. Plagiotropic shoots (horizontal rhizomes) did not begin to develop until 4.3±0.7 years.

Virulence for faba bean and production of ascochitine by Ascochyta fabae

The production of ascochitine by seven isolates of Ascochyta fabae accounted for the toxicity of culture filtrates of the fungus to cells isolated from leaves of Vicia faba. The LD50 value for cells from cultivars that were susceptible, tolerant or resistant to the fungus was similar i.e. 3·0 × 10−5m, 3·8 × 10−5m and 2·9 × 10−5 M, respectively. Ascochitine affected neither the germination of seeds nor the growth of mature plants at 5·17 × 10−4m but caused necrosis and wilting of plant cuttings at 2·5 × 10−4m and 5·10−4m. There was no association between virulence of 16 isolates of A. fabae for three cultivars of V.faba and the production of ascochitine in vitro. One isolate produced no ascochitine in vitro and yet was the most virulent for two of three cultivars. The toxin could not be extracted from infected plants.

Effects of Water and Nutrient Availability on Water Relations, Gas Exchange and Growth Rate of Mature Plants and Resprouts of Arbutus unedo L.

This study examines the effects of water supply and nutrition on the water status, gas exchange and growth of mature plants and resprouts of Arbutus unedo, a Mediterranean evergreen shrub adapted to drought and poor nutrition. Mature plants of A. unedo respond to irrigation with increased leaf water potential during summer drought, but they show a very conservative use of water and they do not increase leaf conductance. There is also a very small increase in net photosynthesis and growth, which does not significantly increase productivity.Resprouts of A. unedo increase water potential, leaf conductance, transpiration rate, net photosynthesis and growth rate in response to watering, showing a less conservative use of water than mature plants. Increased growth rates, both in mature plants and resprouts, are likely to be due to the higher cell turgor caused by improved leaf water potential, rather than to increased photosynthesis.The only effect of nutrient addition on mature plants is an increase in leaf nutrient content, and other aspects of the physiology and growth of resprouts were unaffected. We therefore conclude that water is a more limiting factor than nutrients for mature plants and resprouts of A. unedo growing in the study area. These results support previous data which indicate that higher growth rates in resprouts than in mature plants of A. unedo are mainly the result of a higher water availability.

Correlation between Early and Late Growth Characters in an Improved True Potato Seed Population

A field experiment was conducted at two locations to determine the correlation between seedling and mature plant characters in a large potato (Solanum tuberosum) population developed for production from true potato seed. There was no significant correlation between seedling and reproductive characters, including earliness, at the two locations. Number of internodes and yield per plant were significantly correlated at Huancayo, and at San Ramon, root length and hypocotyl length had a significant correlation with the number of tubers per plant and yield per plant. Although significant, the latter correlations are not high enough to be used to predict the final behavior of genotypes by their seedling traits. Thus, it may be assumed that a certain independence between seedling and mature plant growth characters exists.

Differences in Big Sagebrush (Artemisia tridentata) Plant Stature along Soil-Water Gradients: Genetic Components

Genotypic and phenotypic variations are characteristic among big sagebrush (Artemisia tridentata) plants. One obvious expression is the variability of big sagebrush plant stature along soilwater gradients. Large plants are usually associated with mesic habitats such as drainages or swales, while small plants occupy the xeric portions of the gradients. The purpose of this study was to investigate the genetic influence on big sagebrush plant stature along soil-water gradients. Leaf morphological, phenological, chromatographical, and cytological investigations evaluated potential genetic differences and examined possible subspecies status of the large and small plants. The results of these studies revealed a genetic difference between the large and small plants and confirmed subspecies status. The large plants were identified as basin big sagebrush (A. tridentata spp. tridentata) while the small plants were Wyoming big sagebrush (A. tridentata spp. wyomingensis). Three additional studies examined possible differences in growth potential between the subspecies. A greenhouse and uniform garden study compared seedling and juvenile plant growth. Annual leader growth of mature plants was measured in native populations. Basin big sagebrush plants outgrew Wyoming big sagebrush in the greenhouse, uniform garden, and leader growth experiments. Difference in growth potential between the subspecies may be a consequence of ploidy differences. The most common, important, and widely distributed woody sagebrush (Artemisia L. subgenus tridentatae (Rydb.) E.D. McArthur) is big sagebrush (Artemisia tridentata Nutt.). Big sagebrush is common on millions of hectares throughout western North America from southern Canada to northern Mexico (Beetle 1960, McArthur et al. 1981). This shrub has a wide range of adaptability and grows in various soil types and is associated with numerous plant species from low elevation valleys and plains to high mountain slopes and ridges (Morris et al. 1976, Winward and Tisdalel977, Winward, 1980). Big sagebrush provides browse and habitat for an array of wildlife and livestock, minimizes soil erosion, and is of value in mined-land reclamation. Big sagebrush, as do other plant species, adapts to diverse environments through a combination of phenotypic plasticity and genotypic variation. As Caldwell (1979) theorized, the phenotypic diversity of plants is remarkable, but it is not sufficient to accommodate extensive environmental conditions that are found in the range of a widely distributed species such as big sagebrush. Presently, the big sagebrush complex consists of 4 subspecies (Beetle 1960, Beetle and Young 1965, Goodrich et al. in press, McArthur 1983) which are: basin big sagebrush (A. tridentata Nutt. ssp. tridentata), Wyoming big sagebrush (A. tridentata Nutt. ssp. wyomingensis Beetle and Young), mountain big sagebrush (A. tridentata Nutt. ssp. vaseyana (Rydb.) Beetle), and subalpine sagebrush (A. tridentata Nutt. ssp speciformis (Osterhout) Goodrich and McArthur). Authors are former graduate research assistant and professor, respectively, Department of Range Science, Utah State University, Logan. Authors are presently, lecturer, Department of Botany and Range Management, Somali National University, Mogadishu, Somalia and Vice-President for Research, NPI, 417 Wakara Way, Salt Lake City, Utah 84108. Research was supported by the U.S. Department of Energy and Ecology Center and Department of Range Science, Utah State University. We thank E.D. McArthur for technical assistance, use of laboratory equipment, and review of a draft manuscript. Manuscript accepted 3 July 1985. Genotypic and phenotypic variation is characteristic of big sagebrush (Beetle 1960, Hanks et al. 1973, McArthur et al. 1981, West et al. 1978). An obvious expression is the variability in big sagebrush plant stature along soil-water gradients (Beetle 1960, Hall and Clements 1923, Hanks et al. 1973). Large plants may reach a height of 3.5 to 5.0 m in mesic habitats such as drainages or swales, while plants less than 1.0 m tall are associated with the xeric portions of moisture gradients. Considering the differences in big sagebrush plant stature, a logical question arises: Are the differences in plant stature due to genetic or environmental influences? The research herein discusses the influence of genetics on big sagebrush plant stature. Edaphic differences associated with the large and small big sagebrush plants are reported elsewhere (Barker 1981, Barker and McKell 1983).