Regulated irrigation of woody ornamentals to improve plant quality and precondition against drought stress

Regulated irrigation has the potential to improve crop quality in woody ornamentals by reducing excessive vigour and promoting a more compact habit. This research aimed to compare the effectiveness and the mode of action of two techniques, regulated deficit irrigation (RDI) and partial root drying (PRD), when applied to container-grown ornamentals through drip irrigation. Results showed that RDI and PRD reduced growth in Cotinus coggygria 'Royal Purple', but in Forsythia x intermedia 'Lynwood', significant reductions were recorded only with RDI. Physiological measurements in Forsythia indicated that reductions in stomatal conductance (g(s)) occurred in both treatments, but those in the RDI tended to be more persistent. Reduced g(s) in PRD was consistent with the concept that chemical signals from the root can regulate stomatal aperture alone; however, the data also suggested that optimising the growth reduction required a moderate degree of shoot water deficit (i.e. a hydraulic signal to be imposed). As RDI was associated with tissue water deficit, it was used in a second experiment to determine the potential of this technique to precondition container-grown plants against subsequent drought stress (e.g. during retail stages or after planting out). Speed of acclimation would be important in a commercial context, and the results demonstrated that both slow and rapid imposition of RDI enabled Forsythia plants to acclimate against later drought events. This article discusses the potential to both improve ornamental plant quality and enhance tolerance to subsequent adverse conditions through controlled, regulated irrigation.

Regulated deficit irrigation - a means to control growth in woody ornamentals

Improving plant quality and the uniformity of a crop are major objectives for growers of ornamental nursery stock. The potential to control excess vigour and to improve quality through regulated deficit irrigation (RDI) was investigated using a range of woody ornamental species. RDI regimes reduced vegetative growth consistently across different species and growing seasons. Plants adapted to reduced water supplies primarily via stomatal control, but also by osmotic adjustment when grown under the most severe RDI regimes. Only plants exposed to <= 25% of potential evapo-transpiration demonstrated any evidence of leaf injury, and the extent was slight. Growth inhibition increased as the severity of RDI increased. Improvements in quality were attained through a combination of shorter internodes and final shoot lengths, yet the number of 'formative' primary shoots remained unaffected. Compact, well-branched plants could be formed without a requirement for mid-season pruning. In addition to severity, the timing of RDI also influenced growth responses. Applying 50% ETp for 8 weeks during July-August resulted in the formation of good quality plants, which retained their shape until the following Spring. Re-positioning irrigation drippers within the pots of well-watered plants, in an attempt to induce a partial root drying (PRD) treatment, reduced growth, but not significantly. The adoption of irrigation scheduling, based on 50-100% ETp, has the potential to improve commercial crop quality across a range of ornamental species.

The influence of powdery mildew infection on photosynthesis, chlorophyll fluorescence, leaf chlorophyll and carotenoid content of three woody plant species

The effect of powdery mildew development on photosynthesis, chlorophyll fluorescence, leaf chlorophyll and carotenoid concentrations on three woody plants frequently planted in urban environments was studied. Rates of photosynthetic CO2 fixation were rapidly reduced in two of the three genotypes tested prior to visible signs of infection. Effects on chlorophyll fluorescence (Fo, Fv/Fo, Fv/Fm), leaf chlorophyll and carotenoid content were not manifest until >25 per cent of the leaf area was observed to be covered by mycelial growth indicating reduced photo-synthetic rates during the early stages of infection were not due to degradation of the leaf chloroplast structure. Observation of the fluorescence transient (OJIP curves) showed powdery mildew infection impairs photosynthetic electron transport system by reducing the size but not heterogeneity of the plastoquninone pool, effecting both the acceptor and donor side of photosystem II. Impairment of the photosynthetic electron transport system was reflected by reduced values of a performance index used in this investigation as a measure of photochemical events within photosystem II electron transport. In addition interpretation of the fluorescence data indicated powdery mildew infection may impair the photo-protective process that facilitates the dissipation of excess energy within leaf tissue.

Rapid, automated detection of stem canker symptoms in woody perennials using artificial neural network analysis

Background Pseudomonas syringae can cause stem necrosis and canker in a wide range of woody species including cherry, plum, peach, horse chestnut and ash. The detection and quantification of lesion progression over time in woody tissues is a key trait for breeders to select upon for resistance. Results In this study a general, rapid and reliable approach to lesion quantification using image recognition and an artificial neural network model was developed. This was applied to screen both the virulence of a range of P. syringae pathovars and the resistance of a set of cherry and plum accessions to bacterial canker. The method developed was more objective than scoring by eye and allowed the detection of putatively resistant plant material for further study. Conclusions Automated image analysis will facilitate rapid screening of material for resistance to bacterial and other phytopathogens, allowing more efficient selection and quantification of resistance responses.

Holocene vegetation dynamics in the northeastern Rub' al-Khali desert, Arabian Peninsula: a phytolith, pollen and carbon isotope study

The Holocene vegetation history of the Arabian Peninsula is poorly understood, with few palaeobotanical studies to date. At Awafi, Ras al-Khaimah, UAE, a 3.3 m lake sediment sequence records the vegetation development for the period 8500 cal. yr BP to similar to3000 cal. yr BP. delta(13)C isotope, pollen and phytolith analyses indicate that C3 Pooid grassland with a strong woody element existed during the early Holocene (between 8500 and 6000 cal. yr BP) and became replaced by mixed C3 and C4 grasses with a strong C4 Panicoid tall grass element between 5900 and 5400 cal. yr BP. An intense, arid event Occurred at 4100 cal. yr BP when the lake desiccated and was infilled by Aeolian sand. From 4100 cal. yr BP the vegetation was dominated by C4 Chloridoid types and Cyperaceae, suggesting an incomplete vegetation cover and Aeolian dune reactivation owing to increased regional aridity. These data outline the ecosystem dynamics and carbon cycling in response to palaeomon-soon and north-westerly variability during the Holocene. Copyright (C) 2004 John Wiley Sons, Ltd.

Transgenic approaches to crop improvement

Transgenic crops are now grown commercially on several million hectares, principally in North America. To date, the predominant crops are maize (corn), soybean, cotton, and potatoes. In addition, there have been field trials of transgenics from at least 52 species including all the major field crops, vegetables, and several herbaceous and woody species. This review summarizes recent data relating to such trials, particularly in terms of the trends away from simple, single gene traits such as herbicide and insect resistance towards more complex agronomic traits such as growth rate and increased photosynthetic efficiency. Much of the recent information is derived from inspection of patent databases, a useful source of information on commercial priorities. The review also discusses the time scale for the introduction of these transgenes into breeding populations and their eventual release as new varieties.

The influence of commercial film-forming polymers on reducing salt spray injury in evergreen oak (Quercus ilex L.) and laurel (Prunus laurocerasus L.)

A field trial was undertaken to determine the influence of four commercially available film-forming polymers (Bond [alkyl phenyl hydroxyl polyoxyethylene], Newman Crop Spray 11E™ [paraffinic oil], Nu-Film P [poly-1-p menthene], and Spray Gard [di-1-p menthene]) on reducing salt spray injury on two woody species, evergreen oak (Quercus ilex L.) and laurel (Prunus laurocerasus L.). Irrespective of species, the film-forming polymers Nu-Film-P and Spay Gard did not provide any significant degree of protection against salt spray damage irrespective of concentration (1% or 2%) applied as measured by leaf chlorophyll concentrations, photosynthetic efficiency, visual leaf necrosis, foliar sodium and chloride content, and growth (height, leaf area). The film-forming polymer Newman Crop Spray 11E™ provided only 1-week protection against salt spray injury. The film-forming polymer Bond provided a significant (P < 0.05) degree of protection against salt spray injury 3 months after application as manifest by higher leaf chlorophyll content, photosynthetic efficiency, height and leaf area, and lower visual leaf necrosis and foliar Na and Cl content compared with nontreated controls. In conclusion, results indicate that application of a suitable film-forming polymer can provide a significant degree of protection of up to 3 months against salt spray injury in evergreen oak and laurel. Results also indicate that when applied at 1% or 2% solutions, no problems associated with phytotoxicity and rapid degradation on the leaf surface exist.

Social bees and food plant associations in the Nilgiri Biosphere Reserve, India

The diversity of social bees was assessed at 15 sites across five locations of the Nilgiri Biosphere Reserve, Western Ghats, India, from January to December 2007. We also conducted floristic analyses of local vegetation in each site using one-hectare sample plots. All woody species with a dbh (diameter at breast height) : 30 cm were recorded within the plots. A total area of 9.72 ha was assessed for floristic composition. Similarity of floristic composition between sites was determined using the Jaccard's distance measure and a dendrogram constructed based on the hierarchical clustering of floristic dissimilarities between sites. A Bee Importance Index (BII) was developed to give a measure of the bee diversity at each site. This index was a sum of the species richness of bee species in a site and their visitation frequencies to flowers, calculated as mean flower visits hour 1 within 2 focal patches within one hectare plots. The visits of bee species to flowers were also recorded. The Jaccard distance measure indicated that the montane sites were quite dissimilar to the low elevation sites in floristic diversity. The BII was 7-9 for the wet forest sites and ranged from 4-6 for drier forest sites. Seventy three plant species were identified as social bee plants and of them 45% were visited by one species of bee, 37% by two bee species and 18% by more than two bee species, indicating a certain degree of floral specialization among bees.

Juvenile-mature wood transition in pine: correlation between wood properties and candidate gene expression profiles

There is a strong desire to exploit transcriptomics data from model species for the genetic improvement of non-model crops. Here, we use gene expression profiles from the commercial model Pinus taeda to identify candidate genes implicated in juvenile-mature wood transition in the non-model relative, P. sylvestris. Re-analysis of 'public domain' SAGE data from xylem tissues of P. taeda revealed 283 mature-abundant and 396 juvenile-abundant tags (P < 0.01), of which 70 and 137, respectively matched to genes with known function. Based on sequence similarity, we then isolated 16 putative homologues of genes that in P. taeda exhibited widest divergence in expression between juvenile and mature samples. Candidate expression levels in P. sylvestris were almost invariably differential between juvenile and mature woody tissue samples among two cohorts of five trees collected from the same seed source and selected for genetic uniformity by genetic distance analysis. However, the direction of differential expression was not always consistent with that described in the original P. taeda SAGE data. Correlation was observed between gene expression and juvenile-mature wood anatomical characteristics by OPLS analysis. Four candidates (alpha-tubulin, porin MIP1, lipid transfer protein and aquaporin like protein) apparently had greatest influence on the wood traits measured. Speculative function of these genes in relation to juvenile-mature wood transition is briefly explored. Thus, we demonstrate the feasibility of exploiting SAGE data from a model species to identify consistently differentially expressed candidates in a related non-model species.

Water deficits promote flowering in Rhododendron via regulation of pre and post initiation development

Flowering is generally considered to be advanced by water deficits in many woody perennial species. A long-standing paradigm being that as a plant senses severe environmental conditions resources are diverted away from vegetative growth and towards reproduction before death. It is demonstrated that in Rhododendron flowering is promoted under water deficit treatments. However, the promotion of flowering is not achieved via all increase in floral initiation, but through separate developmental responses. If regulated deficit irrigation (RDI) is imposed prior to the time of initiation, fewer vegetative nodes are formed before the apical meristems switch to floral initiation, and chronologically, floral initiation occurs earlier. Both RDI and partial rootzone drying (PRD) treatments stimulate the development of more flowers Oil each inflorescence if the treatments are continued after the plant has undergone floral initiation. However, floral initiation is inhibited by soil water deficits. If the soil water deficit continues beyond the stages of floral development then anthesis call occur prematurely oil the fully formed floral buds without a need for a winter chilling treatment. It is hypothesised that inhibition of floral initiation in plants experiencing severe soil water deficits results from the inhibitory action Of ABA transportation to the apical meristem from stressed roots. It is demonstrated that ABA applications to well-watered Rhododendron inhibit floral initiation. (c) 2008 Elsevier B.V. All rights reserved.

The effects of photoperiod and light spectrum on stock plant growth and rooting of cuttings of Cotinus coggygria 'Royal Purple'

Extending the season of production and improving the scheduling of ornamental crops are key commercial objectives for nurserymen. In some woody species, the period in which cuttings can be rooted successfully is transient, thus limiting the opportunities for scheduled production. Optimum rooting often occurs in early- to mid-summer coinciding with periods of active shoot growth. The relationship between this shoot activity and root initiation was investigated in Cotinus coggygria 'Royal Purple'. Shoot growth on stock plants was manipulated by altering the photoperiod or light quality. Results indicated there were seasonal effects on rooting, but the importance of shoot activity varied with harvest time. Cuttings harvested in August had high rooting percentages, irrespective of photoperiod, and despite shoot growth terminating in response to the short-day treatment. In contrast, by September, rooting percentage was highest in cuttings from plants under long-days, which had maintained greatest shoot growth activity. Cotinus shoots grown in vitro under 16 h days showed reduced shoot growth and increased rooting competence compared with shoots grown under 8 h days. Growing stock plants under polythene films, which altered the amount and quality of the incident light, influenced the rooting of cuttings harvested in August, but no consistent relationship with shoot activity was apparent. From a practical viewpoint, maintaining shoot activity late in the season may prolong the period for propagation by cuttings; but, from a scientific viewpoint, processes associated with an active shoot apex do not provide a complete explanation of seasonal variation in rooting.

Phylogeny of Pelargonium (Geraniaceae) based on DNA sequences from three genomes

Phylogenetic hypotheses for the largely South African genus Pelargonium L'Hér. (Geraniaceae) were derived based on DNA sequence data from nuclear, chloroplast and mitochondrial encoded regions. The datasets were unequally represented and comprised cpDNA trnL-F sequences for 152 taxa, nrDNA ITS sequences for 55 taxa, and mtDNA nad1 b/c exons for 51 taxa. Phylogenetic hypotheses derived from the separate three datasets were overall congruent. A single hypothesis synthesising the information in the three datasets was constructed following a total evidence approach and implementing dataset specific stepmatrices in order to correct for substitution biases. Pelargonium was found to consist of five main clades, some with contrasting evolutionary patterns with respect to biogeographic distributions, dispersal capacity, pollination biology and karyological diversification. The five main clades are structured in two (subgeneric) clades that correlate with chromosome size. One of these clades includes a "winter rainfall clade" containing more than 70% of all currently described Pelargonium species, and all restricted to the South African Cape winter rainfall region. Apart from (woody) shrubs and small herbaceous rosette subshrubs, this clade comprises a large "xerophytic" clade including geophytes, stem and leaf succulents, harbouring in total almost half of the genus. This clade is considered to be the result of in situ proliferation, possibly in response to late-Miocene and Pliocene aridification events. Nested within it is a radiation comprising c. 80 species from the geophytic Pelargonium section Hoarea, all characterised by the possession of (a series of) tunicate tubers.

Regulation of plant growth in container-grown ornamentals through the use of controlled irrigation

The aim of this research was to determine whether shoot growth could be regulated and plant quality improved through two controlled irrigation techniques: Regulated Deficit Irrigation (RDI) or Partial Root Drying (PRD). An additional benefit of such techniques is that they would also improve the efficiency of irrigation application and reduce the volume of water used on commercial nurseries. Results from two ornamental woody plant species (Cotinus and Forsythia) demonstrated that plant quality could be significantly improved when RDI was applied at ≤ 60% of potential evapo-transpiration (ETp). Stomatal closure and reduced leaf and internode growth rates were associated with both the RDI and PRD techniques, but reduced leaf water potential was only recorded in the RDI system. Changes in xylem sap pH and ABA concentrations were correlated with changes in shoot physiology, and thought to be generated by those roots exposed to drying soil. By adopting such controlled irrigation systems on commercial holdings it is estimated that water consumption could be reduced by 50 to 90%.

Comparative genome analysis provides insights into the evolution and adaptation of Pseudomonas syringae pv. aesculi on Aesculus hippocastanum.

A recently emerging bleeding canker disease, caused by Pseudomonas syringae pathovar aesculi (Pae), is threatening European horse chestnut in northwest Europe. Very little is known about the origin and biology of this new disease. We used the nucleotide sequences of seven commonly used marker genes to investigate the phylogeny of three strains isolated recently from bleeding stem cankers on European horse chestnut in Britain (E-Pae). On the basis of these sequences alone, the E-Pae strains were identical to the Pae type-strain (I-Pae), isolated from leaf spots on Indian horse chestnut in India in 1969. The phylogenetic analyses also showed that Pae belongs to a distinct clade of P. syringae pathovars adapted to woody hosts. We generated genome-wide Illumina sequence data from the three E-Pae strains and one strain of I-Pae. Comparative genomic analyses revealed pathovar-specific genomic regions in Pae potentially implicated in virulence on a tree host, including genes for the catabolism of plant-derived aromatic compounds and enterobactin synthesis. Several gene clusters displayed intra-pathovar variation, including those encoding type IV secretion, a novel fatty acid biosynthesis pathway and a sucrose uptake pathway. Rates of single nucleotide polymorphisms in the four Pae genomes indicate that the three E-Pae strains diverged from each other much more recently than they diverged from I-Pae. The very low genetic diversity among the three geographically distinct E-Pae strains suggests that they originate from a single, recent introduction into Britain, thus highlighting the serious environmental risks posed by the spread of an exotic plant pathogenic bacterium to a new geographic location. The genomic regions in Pae that are absent from other P. syringae pathovars that infect herbaceous hosts may represent candidate genetic adaptations to infection of the woody parts of the tree.

Coppicing shifts CO2 stimulation of poplar productivity to above-ground pools: a synthesis of leaf to stand level results from the POP/EUROFACE experiment

A poplar short rotation coppice (SRC) grown for the production of bioenergy can combine carbon (C) storage with fossil fuel substitution. Here, we summarize the responses of a poplar (Populus) plantation to 6 yr of free air CO2 enrichment (POP/EUROFACE consisting of two rotation cycles). We show that a poplar plantation growing in nonlimiting light, nutrient and water conditions will significantly increase its productivity in elevated CO2 concentrations ([CO2]). Increased biomass yield resulted from an early growth enhancement and photosynthesis did not acclimate to elevated [CO2]. Sufficient nutrient availability, increased nitrogen use efficiency (NUE) and the large sink capacity of poplars contributed to the sustained increase in C uptake over 6 yr. Additional C taken up in high [CO2] was mainly invested into woody biomass pools. Coppicing increased yield by 66% and partly shifted the extra C uptake in elevated [CO2] to above-ground pools, as fine root biomass declined and its [CO2] stimulation disappeared. Mineral soil C increased equally in ambient and elevated [CO2] during the 6 yr experiment. However, elevated [CO2] increased the stabilization of C in the mineral soil. Increased productivity of a poplar SRC in elevated [CO2] may allow shorter rotation cycles, enhancing the viability of SRC for biofuel production.