Differences In Vegetative Growth Research Articles

Effect of Irrigation using Diluted Winery Wastewater on Vitis vinifera L. cv. Cabernet Sauvignon in a Sandy Alluvial Soil in the Breede River Valley - Vegetative Growth, Yield and Wine Quality

Re-use of winery wastewater for irrigation was investigated in a field trial with micro-sprinkler irrigated Cabernet Sauvignon/99Richter in the Breede River Valley region of South Africa. Irrigation with winery wastewater diluted with river water to 100, 250, 500, 1000, 1500, 2000, 2500 and 3000 mg/L chemical oxygen demand (COD) was compared to irrigation with river water. Under the prevailing conditions, plant water status did not respond to irrigation using diluted winery wastewater. Leaf and shoot element contents did not respond consistently to irrigation using diluted winery wastewater. There were no differences in vegetative growth or yield or juice characteristics, with the exception of juice pH. Consequently, water use and water status of the grapevines were also not affected. Results indicated that a summer interception crop may increase the evapotranspiration of vineyards substantially. Irrigation of grapevines using diluted winery wastewater did not have detrimental effects on wine colour and sensory wine characteristics. The grapevines did not respond to level of COD per se . This indicated that sufficient aeration occurred between irrigations which allowed organic carbon breakdown. The low salinity and sodicity levels in the diluted winery wastewater could be a further explanation why the grapevines did not respond to the wastewater irrigation. In heavier soils, regions with lower winter rainfall, situations where the winery wastewater contains more potassium or where no interception crop is cultivated during summer, grapevine responses may be more pronounced.

Application of partial rootzone drying to improve irrigation water use efficiency in grapefruit trees

Partial rootzone drying (PRD) has been reported to potentially improve crop water use efficiency (WUEcrop) compared to full irrigation in different fruit trees; however, field studies on the effect of PRD in citrus are scarce. In this field study, three irrigation strategies were tested in an orchard of mature grapefruit trees during two consecutive seasons (2013/2014 and 2014/2015): drip PRD (two drip lines, alternating irrigation between lines every month), microsprinkler irrigation, and double-line drip irrigation (control). Irrigation was applied during the fruit enlargement stage (April–August). The aims of this field study were: 1) to provide a quantitative comparison of irrigation water productivity among irrigation treatments; and 2) to study their effects on fruit quality, yield, tree growth, and flowering. Drip PRD saved 43 to 47% of irrigation water compared to control irrigation, and microsprinkler irrigation saved 12 to 18% of water compared to control irrigation PRD-irrigated trees maintained or increased yield compared to microsprinkler-irrigated and control trees, depending on the experimental season. Therefore, WUEcrop in PRD-irrigated trees was significantly higher than in control and microsprinkler-irrigated trees at the end of both seasons. Fruit and juice quality parameters were statistically similar among all treatments. PRD irrigation did not reduce the flowering potential of the trees although it delayed the onset of flowering in trees relative to the other treatments in 2013/2014. There was a similar timing of flowering among treatments in 2014/2015 and there were no differences in vegetative growth among the irrigation treatments by the end of March (86 Julian data) in both experimental seasons. Our results suggest that PRD can be economically beneficial for citrus growers who use double-line drip irrigation systems, and a strategy to sustain tree growth, tree health and yield during seasons of extreme drought or when high water restrictions are placed in citrus-producing areas.

Physiological Interaction between Rootstock-Scion: Effects on Xylem Vessels in Cabernet Sauvignon and Merlot Grapevines

The interaction between rootstock and scion can influence the vegetative and productive balance of grapevines. Vascular connections and patterns may be related to the observed phenotype of certain rootstock-scion combinations. However, little is known about the physiology of the rootstock-scion interaction and the related anatomical variables. The aim of this study was to evaluate the effect of the rootstock-scion interaction on the vegetative growth of Vitis vinifera L., with a focus on the vascular system. We investigated the rootstock genotypes 1103 Paulsen (Vitis berlandieri Planch. × Vitis rupestris Scheele), 101-14 Mgt (Vitis riparia Michx. × V. rupestris), and SO4 (V. berlandieri × V. riparia) grafted on the Cabernet Sauvignon and Merlot grapevine varieties. We evaluated vegetative growth variables and performed an image analysis of the vascular system by quantifying the xylem and vessels (diameter, total number, density, and frequency) in different portions (apical, median, and basal) of the scion stem. The rootstock-scion interaction caused differences in vegetative growth and was associated with differences in the vascular system. The vegetative growth of the Cabernet Sauvignon on 1103 Paulsen and Merlot on SO4 combinations was greater than the growths of either variety grafted on 101-14 Mgt. The more vigorous rootstock-scion combinations had vessels with greater mean diameters, xylem areas, and proportion of vessels with diameters greater than 50 μm. Vines grafted on 101-14 Mgt had a greater proportion of vessels with diameters less than 40 μm. The vessel features were altered from the apex to base sections (stem morphology) in all combinations. The physiological interaction between rootstock-scion modified the vascular system in grapevines by altering the xylem vessel.

Sex-related differences in stress tolerance in dioecious plants: a critical appraisal in a physiological context.

Sex-related differences in reproductive effort can lead to differences in vegetative growth and stress tolerance. However, do all dioecious plants show sex-related differences in stress tolerance? To what extent can the environmental context and modularity mask sex-related differences in stress tolerance? Finally, to what extent can physiological measurements help us understand secondary sexual dimorphism? This opinion paper aims to answer these three basic questions with special emphasis on developments in research in this area over the last decade. Compelling evidence indicates that dimorphic species do not always show differences in stress tolerance between sexes; and when sex-related differences do occur, they seem to be highly species-specific, with greater stress tolerance in females than males in some species, and the opposite in others. The causes of such sex-related species-specific differences are still poorly understood, and more physiological studies and diversity of plant species that allow comparative analyses are needed. Furthermore, studies performed thus far demonstrate that the expression of dioecy can lead to sex-related differences in physiological traits-from leaf gas exchange to gene expression-but the biological significance of modularity and sectoriality governing such differences has been poorly investigated. Future studies that consider the importance of modularity and sectoriality are essential for unravelling the mechanisms underlying stress adaptation in male and female plants growing in their natural habitat.

An ATP-dependent protease homolog ensures basic standards of survival and pathogenicity for Magnaporthe oryzae

The occurrence of fungal disease of crops requires a susceptible host, a virulent race, and a favourable environment. Environmental factors play crucial roles and ultimately determine epidemic of disease in host-pathogen interactions. However, the molecular basis of how fungi cope with environments still needs further research. Here, we characterized a lesion-restricted mutant of Magnaporthe oryzae, in which a M agnaporthe ATP-dependent Protease homolog (MAP1) was disrupted by a T-DNA insertion. The gene deletion and complementation transformants (ΔMAP1, ΔMAP1/MAP1) were genetically created and functionally analyzed. Under optimum conditions, no visible phenotypic variations were found in ΔMAP1; but under selected stresses, the significant difference in vegetative growth between ΔMAP1 and wild type (or ΔMAP1/MAP1) emerged, clearly reflecting a causal relationship between MAP1 and stress resistance. The MAP1 protein was subcellularly localized in mitochondria. When subjected to oxidative stress, ΔMAP1 mitochondria were more susceptible to damage than that of the wild type. Linking the decreased virulence in ΔMAP1, we thus propose MAP1, as a protective factor, is required for plant infection and multi-stress resistance. Above all, the MAP1 mutation implies a basic requirement for disease development in the field and a potential implication in crop protection.

Adaptation In Atriplex Griffithii and Prosopis Juliflora Plants In Response To Cement Dust Pollution

In the present study, we attempted to determine the effects of cement dust on the adaptations of plants growing in polluted area and to compare it with a leeward site (control) of the cement factory that was unpolluted. The emphasis was also given to observe the effects of cement dust on the soil characteristics of the factory area. The introduction of cement dust from a cement factory produced negative effects on the morphological traits of both plant species ( Atriplex griffithii and Prosopis juliflora ) growing at the polluted as compared to unpolluted area. Low seedling height and plant circumference for A. griffithii andi were observed at the polluted site of the cement factory. A. griffithii showed significant reduction in leaf area growing at the polluted site as compared to control site. Similarly, a significant (p<0.05) reduction in leaf area was also recorded for P. juliflora at the polluted sites. The growth pattern of A. griffithii and P. juliflora looked more greener, better in plant height and healthier as observed at unpolluted sites. No significant difference in vegetative growth for both plant species for plant height and circumference was seen at the polluted sites of the factory. We believe that the underlying edaphic factor and genotypic ability of both species helped to some extent in adaptation to the extreme habitat conditions at the polluted sites. The significance differences in soil pH level and organic matter contents were recorded from polluted area as compared to control site. © JASEM

VeA and LaeA transcriptional factors regulate ochratoxin A biosynthesis in Aspergillus carbonarius

Ochratoxin A (OTA) is a mycotoxin with nephrotoxic, teratogenic and immunotoxic properties which represents a serious risk for human and animal health. Aspergillus carbonarius is considered the main OTA-producing species in grapes and products such as raisins, wine or juices, although it has also been isolated from coffee, cocoa and cereals. Till now not much information is available about regulatory mechanisms of OTA production by A. carbonarius. A better understanding of how environmental factors influence OTA production and which genes are involved in its regulation could help us design new control strategies. In this study, we have evaluated the role of VeA and LaeA transcriptional factors, which have been shown to regulate secondary metabolism in response to light in A. carbonarius. To this aim, veA and laeA genes were deleted in an ochratoxigenic A. carbonarius strain by targeted gene replacement using Agrobacterium tumefaciens-mediated transformation. Loss of veA and laeA in A. carbonarius yields to an organism with slight differences in vegetative growth but a strong reduction in conidial production. A drastic decrease of OTA production that ranged from 68.5 to 99.4% in ΔveA and ΔlaeA null mutants was also observed, which was correlated with a downregulation of a nonribosomal peptide synthetase involved in OTA biosynthesis. These findings suggest that VeA and LaeA have an important role regulating conidiation and OTA biosynthesis in response to light in A. carbonarius in a similar way to other fungi where functions of VeA and LaeA have been previously described. This is the first report of a transcriptional factor governing the production of OTA by A. carbonarius.

Metabolic engineering of raffinose-family oligosaccharides in the phloem reveals alterations in carbon partitioning and enhances resistance to green peach aphid

Many plants employ energized loading strategies to accumulate osmotically-active solutes into the phloem of source organs to accentuate the hydrostatic pressure gradients that drive the flow of water, nutrients and signals from source to sinks. Proton-coupled symport of sugars from the apoplasm into the phloem symplasm is the best studied phloem-loading mechanism. As an alternative, numerous species use a polymer trapping mechanism to load through symplasm: sucrose enters the phloem through specialized plasmodesmata and is converted to raffinose-family oligosaccharides (RFOs) which accumulate because of their larger size. In this study, metabolic engineering was used to generate RFOs at the inception of the translocation stream of Arabidopsis thaliana, which loads from the apoplasm and transports predominantly sucrose, and the fate of the sugars throughout the plant determined. Three genes, GALACTINOL SYNTHASE, RAFFINOSE SYNTHASE and STACHYOSE SYNTHASE, were expressed from promoters specific to the companion cells of minor veins. Two transgenic lines homozygous for all three genes (GRS63 and GRS47) were selected for further analysis. Three-week-old plants of both lines had RFO levels approaching 50% of total soluble sugar. RFOs were also identified in exudates from excised leaves of transgenic plants whereas levels were negligible in exudates from wild type (WT) leaves. Differences in starch accumulation between WT and GRS63 and GRS47 lines were not observed. Similarly, there were no differences in vegetative growth between WT and engineered plants, but the latter flowered slightly earlier. Finally, since the sugar composition of the translocation stream appeared altered, we tested for an impact on green peach aphid (Myzus persicae Sulzer) feeding. When given a choice between WT and transgenic plants, green peach aphids preferred settling on the WT plants. Furthermore, green peach aphid fecundity was lower on the transgenic plants compared to the WT plants. When added to an artificial diet, RFOs did not have a negative effect on aphid fecundity, suggesting that although aphid resistance in the transgenic plants is enhanced, it is not due to direct toxicity of RFO toward the insect.

Tolerance to ion toxicities enhances wheat (Triticum aestivum L.) grain yield in waterlogged acidic soils

The high concentrations of Mn, Fe and Al in acid soils during waterlogging impair root and shoot growth more severely in intolerant than tolerant wheat genotypes. This study aims to establish whether this difference in vegetative growth and survival during waterlogging (1) is verifiable across a range of tolerant/intolerant genotypes and acid soils, and (2) results in improved recovery after cessation of waterlogging and enhanced grain yield. Wheat genotypes contrasting in their tolerance to ion toxicities were grown in four acid soils until 63DAS and maturity, with a 42-day waterlogging treatment imposed at 21 DAS. The shoot Al, Mn and Fe concentrations increased by up to 5-, 3- and 9-fold respectively due to waterlogging in various soils. Compared to the intolerant lines, Al-, Mn- and Fe-tolerant genotypes maintained a relatively lower increase in shoot concentrations of Al (79 vs. 117%), Mn (90 vs. 101%) and Fe (171 vs. 252%) and demonstrated better waterlogging tolerance at the vegetative stage expressed in relative root (38% vs. 25%) and shoot (62% vs. 52%) growth. After cessation of waterlogging and the continued growth to maturity, tolerant genotypes maintained a relatively lower plant concentration of Al, Mn and Fe, but produced a higher above-ground biomass (74% vs. 56%) and most importantly demonstrated improved waterlogging tolerance (a relative grain yield of 78% vs. 54%) compared to intolerant genotypes. Maturity following waterlogging stress was delayed less in tolerant than intolerant genotypes (114 vs. 124%, respectively), which would reduce the potential yield loss where post-anthesis coincides with drought. The results confirm the validity of a novel approach of enhancing waterlogging tolerance of wheat genotypes grown in acid soil via increased tolerance to ion toxicities.

A Sense of Self: Exploring the Selfing Syndrome in Capsella

Over the course of angiosperm evolution, inbreeding or selfing lineages have evolved independently numerous times from selfincompatible outbreeding ancestors. One of the driving forces of the evolution of selfing is thought to be limited pollinator and/or mate availability under low population densities (Lloyd, 1992). The breakdown in self-incompatibility that occurs during the transition to selfing typically is accompanied by specific changes in flower morphology and function, known as the selfing syndrome. Compared with their outbreeding relatives, selfing species tend to have smaller flowers that open less, develop a shorter distance between stigma and anthers, and produce less pollen, nectar, and scent (reviewed in Sicard and Lenhard, 2011). New work by Sicard et al. (2011) explores the genetic and molecular basis of these selfing syndrome traits in the genus Capsella, a close relative of Arabidopsis, through genetic mapping of a recombinant inbred line population from a cross between the selfing species Capsella rubella and outbreeding Capsella grandiflora. C. rubella exhibits many of the typical selfing syndrome traits, such as smaller size and opening angle of petals, shorter distance between stigma and anthers, and reduced pollen-to-ovule ratio (see figure). Analysis of the recombinant inbred line population led to the identification of multiple independent quantitative trait loci influencing these traits, suggesting independent evolution of different traits. The authors concluded that the selfing syndrome in Capsella has a complex genetic basis resulting fromthe accumulated effects of mutations at multiple genetic loci. An assessment of a variety of flower, leaf, and growth traits indicated that the main difference between the two species is in their flower morphology, and the floral differences are independent from differences in vegetative growth and development. The morphological traits associated with the selfing syndrome have been proposed to increase the efficiency of self-pollination relative to the outbreeder. The authors tested this hypothesis using an elegant approach by introgressing the S-locus of C. rubella into C. grandiflora. This resulted in introgression lines that were fully selfcompatible but with floral morphology very similar to the C. grandiflora outbreeder. Experiments with these lines suggested that flower morphology in C. rubella, and in particular the reduction in flower opening, is more conducive to efficient self-pollination than that of C. grandiflora. Thus, selfing syndrome flower traits may be selected for directly because of their positive effect on efficient self-pollination. Analysis of different C. rubella accessions showed that the small flower size and opening angle of petals are fixed traits within the species, consistent with a single origin for these traits. This is of interest as C. rubella is geographically far more widespread than C. grandiflora. Further studies, including the identification of genes underlying quantitative trait loci associated with the selfing syndrome in Capsella species, are necessary to determine the timing of the breakdown in self-incompatibility versus the evolution of morphological traits and the primary forces driving evolution.

Soil organic carbon pools and composition in a wetland complex invaded by reed canary grass

Reed canary grass (Phalaris arundinacea) invasion is prevalent in wetlands and riparian fringes, and due to differences in vegetative growth and residue quality relative to native species, P. arundinacea invasion could result in measurable effect on soil organic carbon (SOC) pools and composition. To examine these questions, plant biomass and soil samples were collected from areas invaded by P. arundinacea and areas colonized either by a native sedge Scirpus cyperinus or a mixed assemblage of 22 native species in a south-central Indiana (USA) wetland. Plant biomass composition (C, N, cellulose, lignin, and phenolics), total and water-extractable SOC pools were determined. S. cyperinus biomass contained (g kg−1 biomass) significantly (P < 0.05) more lignin (142.5 vs 72), phenolics (29.2 vs 11.2), and cellulose (260.5 vs 164.8) than P. arundinacea biomass. These constituents were also more abundant in mixed native plant material than in P. arundinacea biomass. Decomposition of plant biomass was related to residue composition with P. arundinacea shoot biomass decomposing 1.6 times faster than S. cyperinus material. SOC pools (Mg C ha−1, 0–30 cm) were larger under P. arundinacea (28.3) than under either S. cyperinus (23.9) or the mixed native species (21.8). Thus, the greater recalcitrance of native plant biomass did not translate into larger SOC pools. Furthermore, water-extractable organic C, N, and carbohydrates were significantly higher in the surface layer of soils supporting P. arundinacea than in native species. These results therefore indicate a clear effect of P. arundinacea invasion on the cycling and composition of soil organic matter at the study site.

Short-term effect of beach replenishment on a shallow Posidonia oceanica meadow

Putative perturbations on a Posidonia oceanica meadow produced by recent artificial beach nourishment were evaluated in relation to four undisturbed meadows. Temporal variations of putative impacted location vs. control locations of environmental (light availability and sediment features), plant (associated epiphytes, silt–clay fraction attached to epiphytes, herbivore attack, non-structural carbohydrate reserves) and structural parameters (cover and density) of meadows were tested by asymmetrical analysis of variance beyond BACI (Before/After, Control/Impact). Additionally, two asymmetrical analyses of variance were used to test for differences in vegetative growth of horizontal rhizomes (leaf production, horizontal rhizome growth, biomass production and net secondary rhizome recruitment) before and after beach replenishment. Environmental effects induced by dumping works were only detected in connection with a higher silt–clay deposition rate. This increase was consistent with the increase of silt–clay cover attached to epiphytes. As a consequence of silt–clay smothering, a decrease of filter feeding epiphytes, starch reserves, shoot surface and shoot biomass was observed. The sensitivity of plants to sediment inputs, leads us to recommend avoidance of dumping or sediment movement in the vicinity of P. oceanica meadows.

Physiologic and metabolic responses of wheat seedlings to elevated and super-elevated carbon dioxide

The metabolic consequence of suboptimal (400 μmol mol −1 or ppm), near-optimal (1500 ppm) and supra-optimal (10,000 ppm) atmospheric carbon dioxide concentrations [CO 2] was investigated in an attempt to reveal plausible underlying mechanisms for the differential physiological and developmental responses to increasing [CO 2]. Both non-targeted and targeted metabolite profiling by GC–MS and LC–MS were employed to examine primary and secondary metabolites in wheat ( Triticum aestivum, cv Yocoro rojo) continuously exposed to these [CO 2] levels for 14, 21 and 28 days. Metabolite profile was altered by both [CO 2] and physiological age. In general, plants grown under high [CO 2] exhibited a metabolite profile characteristic of older plants under ambient CO 2. Elevated [CO 2] resulted in higher levels of phosphorylated sugar intermediates, though no clear trend in the content of reducing sugars was observed. Transient starch content was enhanced by increasing [CO 2] to a much greater extent at 10,000 ppm CO 2 than at 1500 ppm CO 2. The percentage increase of starch content resulting from CO 2 enrichment declined as plants develope. In contrast, elevated [CO 2] promoted the accumulation of secondary metabolites (flavonoids) progressively to a greater extent as plants became mature. Elevated [CO 2] to 1500 ppm induced a higher initial growth rate, while super-elevated [CO 2] appeared to negate such initial growth promotion. However, after 4 weeks, there was no difference in vegetative growth between 1500 and 10,000 ppm CO 2-grown plants, both elevated CO 2 levels resulted in an overall 25% increase in biomass over the control plants. More interestingly, elevated atmospheric [CO 2] reduced evapotranspiration rate (ET), but further increase to the supra-optimal level resulted in increased ET (a reversed trend), i.e. ET at 1500 ppm < ET at 10,000 ppm < ET at 400 ppm. The differential effect of elevated and super-elevated CO 2 on plants was further reflected in the nitrogen dynamics. These results provide the potential metabolic basis for the differential productivity and stomatal function of plants grown under elevated and super-elevated CO 2 levels.

Influence of Vineyard Floor Management Practices on Grapevine Vegetative Growth, Yield, and Fruit Composition

The viticultural effects of sward competition with vines for water and nutrients, indirectly resulting from reduced herbicide use under a sustainable production system, are well established in cooler, more humid areas but are less well understood in warm and dry areas. Three groundcover treatments—standard industry practice of herbicide-treated undervine strips, bare soil maintained with herbicides, and complete floor cover (no herbicides)—were applied in two Chardonnay vineyards, one in a hot dry climate, the other in a mild climate. Increasing floor cover decreased early-season soil moisture and petiole nutrient status and strongly reduced vine vegetative growth. After three experimental years, grape yield also became limited. Large treatment differences in vegetative growth, canopy structure, and yield contributed to differences in berry weight and composition. Vine response to floor covers was less pronounced under mild climatic conditions compared to hot and dry conditions. Total or partial floor cover is a powerful tool for controlling vegetative growth of grapevines. However, under hot and dry conditions, competition for water and nutrients, particularly if it occurs at sensitive stages (such as bloom and berry set) can lead to a substantial decrease in yield and vine capacity.

Changes in growth, gas exchange, xylem hydraulic properties and water use efficiency of three olive cultivars under contrasting water availability regimes

Differences in vegetative growth, gas exchange, xylem hydraulic properties and water use efficiency of biomass production were investigated on young plants of three Olea europaea L. cultivars (Cobrançosa, Madural and Verdeal Transmontana), submitted to contrasting water availability regimes. Low water availability (LW) affected growth and biomass accumulation of the three cultivars. However, Cobrançosa plants were the less affected. Under LW conditions, total leaf area was sharply reduced due to a combination of leaf growth reduction and shedding of older leaves, minimising water losses by transpiration. Water stress also caused a marked decline on photosynthetic capacity and stomatal control was the major factor affecting photosynthesis. Under LW, water use efficiency of biomass production was improved in Cobrançosa, whereas it decreased considerably in Madural and Verdeal Transmontana. In all cultivars, water stress induced an increase in xylem vessel frequency, providing a greater vascular potential and a greater security of xylem sap conduction under drought conditions. From the behaviour of Cobrançosa plants, with a lower allocation of assimilates to leaves, smaller leaves, a smaller reduction in net assimilation rate and photosynthetic rate, a more efficient water transport through the xylem, and a more enhanced water use efficiency of biomass production under LW, we consider this cultivar very promising for cultivation in semi-arid areas.

Ecological fitness of a glyphosate-resistant Lolium rigidum population: Growth and seed production along a competition gradient

Repeated use of glyphosate has resulted in evolution of glyphosate-resistant Lolium rigidum populations in Australia. The relative growth, competitiveness and reproductive output of glyphosate resistant (R) and susceptible (S) L. rigidum phenotypes from a single population were compared in competition with wheat. Vegetative growth of R and S individuals was studied in response surface experiments in the glasshouse and seed production was measured using an additive neighbourhood design experiment conducted in pots outside during the normal growing season of L. rigidum in Australia. There were no significant differences in vegetative growth or competitiveness of the R and the S phenotypes. The mean weight of seeds produced by R plants was significantly greater than that produced by S individuals. In the absence of wheat and at tow wheat densities, S plants produced more seeds than R plants. However, at higher crop densities, differences in seed production were not significant. This is the first study to compare components of fitness at key life history stages for glyphosate R and S phenotypes isolated from a single weed population. The results presented indicate important differences in resource allocation during the reproductive stage for R and S phenotypes. Subtle differences in life history strategies may be manipulated by agronomic management to exploit the potential ecological fitness costs of the R phenotype. Further studies are required to provide a greater understanding of the occurrence and extent of fitness costs associated with glyphosate resistance. This knowledge can then be incorporated into models that simulate resistance evolution to design management strategies to prevent and/or contain the spread of glyphosate resistance. (C) 2006 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.

Contributions of Heterosis and Epistasis to Hybrid Fitness

Early-generation hybrid fitness is difficult to interpret because heterosis can obscure the effects of hybrid breakdown. We used controlled reciprocal crosses and common garden experiments to distinguish between effects of heterosis and nuclear and cytonuclear epistasis among morphotypes and advanced-generation hybrid derivative populations in the Piriqueta caroliniana (Turneraceae) plant complex. Seed germination, growth, and sexual reproduction of first-generation hybrids, inbred parental lines, and outbred parental lines were compared under field conditions. Average vegetative performance was greater for hybrids than for inbred lines, and first-season growth was similar for hybrids and outbred parental lines. Hybrid survival surpassed that of inbred lines and was equal to or greater than outbred lines' survival, and more F(1) than parental plants reproduced. Reductions in hybrid fitness due to Dobzhansky-Muller incompatibilities (epistasis among divergent genetic elements) were expressed as differences in vegetative growth, survival, and reproduction between plants from reciprocal crosses for both F(1) and backcross hybrid generations. Comparing performance of hybrids against parental genotypes from intra- and interpopulation crosses allowed a more robust prediction of F(1) hybrids' success and more accurate interpretations of the genetic architecture of F(1) hybrid vigor.

Cluster Thinning Effects on Three Deficit-IrrigatedVitis viniferaCultivars

Crop load adjustment is widely accepted as an important vineyard management tool for premium-quality wine production. However, little information is available on its effectiveness under warm, dry climatic conditions. Crop loads were altered on three own-rooted winegrape cultivars grown in a mature, deficit-irrigated vineyard in the arid Yakima Valley (Washington) over a five-year period (1997 to 2001). Thinning consisted of preferentially removing clusters on shoots not arising from nodes deliberately retained at pruning, either one month after bloom or at veraison, to achieve target yields for Cabernet Sauvignon (6.7 t/ha), Riesling (9.0 t/ha), and Chenin blanc (11.2 t/ha). Removing, on average, 39% of the clusters from Cabernet Sauvignon, 30% from Riesling, and 38% from Chenin blanc reduced yields by 36%, 17%, and 20%, respectively. Average crop loads varied from 6.7 to 14.8 kg fruit/kg pruning weight for nonthinned vines and from 4.4 to 9.2 for thinned vines, and average yields varied from 7 to 25 t/ha for nonthinned vines and from 5 to 16 t/ha for thinned vines, depending on cultivar and season. Cluster thinning and its timing had little or no influence on shoot growth, leaf area, pruning weight, berry number, berry weight, and fruit composition (soluble solids, titratable acidity, pH, color) in both the current and subsequent seasons. Differences in vegetative growth, yield formation, and fruit composition within cultivars were mostly due to season (including weather and soil moisture) rather than to yield or crop load.

Recovery of deep Posidonia oceanica meadows degraded by trawling

The recovery capacity of meadows of the Mediterranean seagrass Posidonia oceanica (L.) Delile in an area affected by illegal trawling were assessed after protection by anti-trawling reefs. The differences in vegetative growth between two impacted and two undisturbed localities were tested using growth, shoot balance, aborted branches, and leaf and rhizome production of both plagiotropic and orthotropic rhizomes. The organic matter in sediments, silt clay fraction and light intensity incident on the bottom were also measured in order to evaluate the physical conditions. Environmental and plant variables were measured in three sites placed inside each locality. The vegetative growth was positive in both impacted and control meadows but growth rates were lower in impacted than in control meadows. Average growth, production and shoot balance were greater in plagiotropic rhizomes from undisturbed localities (40.7±1.75 vs. 28.4±1.34 mm/year, 1133±0.06 vs. 708±0.04 mg DW/shoot/year, 1.36±0.08 vs. 0.96±0.06 shoots/year, respectively). Significantly greater values were also found in undisturbed localities for orthotropic rhizomes in terms of shoot balance and rhizome production (0.07±0.01 vs. 0.01±0.003 shoots/shoot/year and 155 vs. 124 mg DW/shoot/year, respectively). Of the physical parameters measured, only light intensity differed significantly between impacted and undisturbed localities. This parameter was 15.5% to 67.6% lower in impacted localities than in undisturbed localities, and this is the factor that causes the retardation of vegetative growth. The results show that recovery of P. oceanica meadows is possible after eliminating the cause of the impact. However, the very low rates of vegetative growth may prolong the time to total recuperation to almost 100 years. Therefore, effective management of P. oceanica meadows should aim to prevent meadow loss.

Patterns of Genetic Variation and Demography of Cycas taitungensis in Taiwan

Cycas taitungensis Shen, Hill, Tsou & Chen is an endemic species remaining in two remnant populations in southeastern Taiwan. Ecological studies showed that the sex ratio between female and male of the main population is approximately 1.7:1. Leaf production was found to be correlated with tree height before reaching 1 m in length (r = 0.95). The annual reproduction rate of female plants is highly variable, with seed numbering between 80 and 400 in each tree. The site study revealed a significant difference in vegetative growth and age structure between the subpopulations collected in two opposite microhabitats. Genetic studies using isozyme analysis showed low genetic variability (HE = 0.039) and little genetic differentiation between the populations (FST = 0.051). The genetic data are well correlated with the ecological observation that the differences reflect various microhabitat effects within a very local environment and that the impact influenced the extent of the degree of genetic differentiation within local populations. This work presents extensive genetic information forC. taitungensis that give rise to more ecological and genetic insights into the plant for better establishment of in situ and ex situ conservation programs.