Gordon Rogers

Source–sink manipulation to increase melon (Cucumis melo L.) fruit biomass and soluble sugar content

Various source–sink perturbations were employed to alter partitioning to orange flesh melon (Cucumis melo L. reticulatus group) and thus to influence fruit biomass and soluble sugar content (indexed as total soluble solids of fruit juice, % TSS), with attention given to the timing of treatment application. A strong relationship existed between harvest index and fruit mass (r2 = 0.88) in control plants, whereas the correlation with fruit TSS was poor (r2 = 0.11). Augmentation of assimilate supply to fruit early in fruit development (before approx. 21 days before harvest, DBH) resulted in more fruit set and increased fruit biomass, whereas augmentation after 21 DBH resulted in increased fruit TSS. Thus, fruit biomass was increased (1644 cf. 1442 g FW per fruit for control, P = 0.02), but not TSS, on plants in which fruit set was delayed (source biomass increased, harvest index decreased from 59% for control to 38%). Treatment of plants with a cytokinin-based vegetative growth inhibitor at 14 DBH produced fruit with higher TSS (11.3 cf. 10.7% for control). Thinning fruit to leave 1 fruit per plant 1 week before harvest increased the proportion of fruit in a population that exceeded a quality control standard of 10% TSS from 20 to 80%. Variations in plant response with timing of treatment application are interpreted in terms of fruit development (cell division, cell expansion, and sugar accumulation phases). Although a detriment to yield (15 cf. 31 t/ha for control), the fruit thinning treatment was recommended for commercial use and a simple model was developed to calculate the required farm-gate price of fruit to make thinning economically viable.

Canopy development and hydraulic function in Eucalyptus tereticornis grown in drought in CO2-enriched atmospheres

We report on the relationship between growth, partitioning of shoot biomass and hydraulic development of Eucalyptus tereticornis Sm. grown in glasshouses for six months. Close coordination of stem vascular capacity and shoot architecture is vital for survival of eucalypts, especially as developing trees are increasingly subjected to spasmodic droughts and rising atmospheric CO2 levels. Trees were exposed to constant soil moisture deficits in 45 L pots (30-50% below field capacity), while atmospheric CO2 was raised to 700 μL CO2 L-1 in matched glasshouses using a hierarchical, multi-factorial design. Enrichment with CO2 stimulated shoot growth rates for 12-15 weeks in well-watered trees but after six months of CO2 enrichment, shoot biomasses were not significantly heavier (30% stimulation) in ambient conditions. By contrast, constant drought arrested shoot growth after 20 weeks under ambient conditions, whereas elevated CO2 sustained growth in drought and ultimately doubled the shoot biomass relative to ambient conditions. These growth responses were achieved through an enhancement of lateral branching up to 8-fold due to CO2 enrichment. In spite of larger transpiring canopies, CO2 enrichment also improved the daytime water status of leaves of droughted trees. Stem xylem development was highly regulated, with vessels per unit area and cross sectional area of xylem vessels in stems correlated inversely across all treatments. Furthermore, vessel numbers related to the numbers of leaves on lateral branches, broadly supporting predictions arising from Pipe Model Theory that the area of conducting tissue should correlate with leaf area. Diminished water use of trees in drought coincided with a population of narrower xylem vessels, constraining hydraulic capacity of stems. Commensurate with the positive effects of elevated CO2 on growth, development and leaf water relations of droughted trees, the capacity for long-distance water transport also increased.

Some perspectives on rocket as a vegetable crop: a review

Some Perspectives on Rocket as a Vegetable Crop: A Review Baby leaf rocket is consumed worldwide as a salad vegetable. It is usually mixed with other baby leaf crops, such as spinach and lettuce, to form a mesclun-type salad. Rocket crops have become popular due to their distinct taste and textural appearance in mixed salads. There are two common forms of rocket that are commercially cultivated, a perennial species (Diplotaxis tenuifolia (L.) DC.) known as perennial wall rocket and an annual species (Eruca sativa Mill.) known as annual garden rocket. The popularity of baby leaf crops has increased in recent years due to consumer demand for a convenient, nutritious and easily accessible product. The baby leaf salad sector is now a significant part of the leafy vegetable market, with growth in this sector estimated to continue. The leaves of cultivars of perennial wall rocket and annual garden rocket have been bred to look similar, allowing for a year-round supply of produce. Despite this, there are many differences between the species that affect their responses to abiotic factors during growth and storage. This paper aims to provide some perspectives on the historical importance, botanical classification and cultivation techniques of these economically important plants. Rokietta Jako Roślina Warzywna: Przegląd Młoda rokietta liściasta spożywana jest na całym świecie jako warzywo sałatkowe. Miesza się ją zazwyczaj z innymi młodymi warzywami liściastymi, takimi jak: szpinak i sałata, by otrzymać sałatkę typu mesclun. Rośliny rokietty stały się popularne ze względu na ich specyficzny smak i wygląd w sałatkach mieszanych. Istnieją dwa powszechnie spotykane rodzaje rokietty, które są uprawiane komercyjnie: gatunek wieloletni - dwurząd wąskolistny (ang. perennial wall rocket) (Diplotaxis tenuifolia (L.) DC.) i gatunek jednoroczny - rokietta siewna (ang. garden rocket) (Eruca sativa Mill.). Popularność młodych roślin liściastych wzrosła w ostatnich latach ze względu na zapotrzebowanie konsumentów na pożywne i łatwo dostępne produkty. Sektor sałatek z młodych liści stanowi już znaczącą część rynku warzyw liściastych i spodziewany jest dalszy rozwój w tym sektorze. Liście odmian uprawnych dwurządu wąskolistnego i rokietty siewnej wyhodowano tak, że są do siebie podobne, co pozwala na dostawę tego produktu przez cały rok. Pomimo tego, istnieje wiele różnic między tymi gatunkami, które mają wpływ na ich reakcje na czynniki abiotyczne w okresie wzrostu i przechowywania. Niniejszy artykuł ma na celu przedstawienie historycznego znaczenia, klasyfikacji botanicznej i techniki uprawy tych ważnych gospodarczo roślin.

Influence of Storage Temperature on the Seasonal Shelf Life of Perennial Wall Rocket and Annual Garden Rocket

Baby leaf crops, particularly leaves from plants commonly known as rocket, account for an increasing proportion of the global salad market due to their distinctive taste and texture. It is important to determine the effect of preharvest abiotic factors on the shelf life of these crops in order to improve the supply of quality produce with an appropriately long shelf life. The visual shelf life of minimally processed leaves of perennial wall rocket (Diplotaxis tenuifolia [L.] DC.) and annual garden rocket (Eruca sativa Mill.) were assessed across different harvest number, season, and storage temperature conditions. A separate experiment examined the effect of fertilizer rate on the shelf life of rocket crops. The shelf life of leaves from three growing seasons were determined at 0, 4, and 7°C, and leaves grown with various nitrogen rates were stored at 0°C. There was an interaction between harvest number, season, and storage temperature for both rocket crops, with storage at lower temperatures consistently resulting in longer shelf life. Under these conditions, the shelf life of perennial wall rocket was longest for the second harvest of the summer planting; for annual garden rocket the second harvest of the winter planting had the longest shelf life. The reasons for the response maybe related to differences in the carbon fixation and reproductive cycles of these plants. Substantial differences in shelf life across harvest number and season occurred for perennial wall rocket, where there was a variation in shelf life of 12 to 26 days when stored at 4°C. For annual garden rocket, an interaction among cultivar, harvest number, and season occurred, with the cv. Highway [ES5] having a shorter shelf life than the other cultivars for the first harvest of the winter planting. Nitrogen rate did not affect the shelf life of either crop. To achieve maximum shelf life, leaves should be stored at about 0°C.

Factors Affecting Growth of Perennial Wall Rocket and Annual Garden Rocket

Popularity of baby leaf salad crops has increased and is likely to continue. Despite their commercial importance, cultivation of these crops is limited by a lack of appropriate production systems. It is important to establish abiotic constraints for efficient production of these crops to improve supply and quality. In separate experiments, responses of perennial wall rocket (Diplotaxis tenuifolia [L.] DC.) and annual garden rocket (Eruca sativa Mill.) to harvest number, seasonal conditions, and fertilizer level were measured. The yield of perennial wall rocket was influenced by the interaction between the cultivar, harvest number, and season. No clear response between these factors was identified, with the highest yields for the cvs. European wild rocket [DT1] and Apollo [DT2] for the first harvest summer crop (2.7 and 2.8 kg/m2, respectively) and the cv. Nature [DT3] for the second harvest summer and spring crops (2.5 kg/m2, respectively). For annual garden rocket, there was an interaction between the yield and season with the highest yield during summer (3.3 kg/m2), followed by winter (2.7 kg/m2) and spring (1.9 kg/m2). Nitrogen rate did not affect yield or dry weight for either crop, meaning that the species require only little additional nitrogen for efficient growth, and crops may currently be overfertilized. Optimal production is achieved during spring and summer for perennial wall rocket and summer and winter for annual garden rocket, allowing for the interchangeable use of species throughout the growing seasons. The growth of perennial wall rocket improves from first to second harvest but decreases for annual garden rocket, meaning that the perennial species is better suited to at least two harvests.

Variations in the most abundant types of glucosinolates found in the leaves of baby leaf rocket under typical commercial conditions

BACKGROUND Changes in the concentration of the three most abundant glucosinolates were measured in the leaves of perennial wall rocket [Diplotaxis tenuifolia (L.) DC.], and annual garden rocket (Eruca sativa Mill.). HPLC-MS was used to identify glucoraphanin, 4-hydroxyglucobrassin and glucoerucin from perennial wall rocket, and glucoraphanin, glucobrassicin and 4-methoxyglucobrassicin from annual garden rocket. In separate experiments the responses of glucosinolates to harvest number, seasonal conditions, nitrogen supply and post-harvest storage conditions were measured. RESULTS For perennial wall rocket, season influenced the concentration of glucoraphanin, which were highest for the spring [379 µg kg(-1) fresh weight (FW)] and summer (317 µg kg(-1) FW) plantings. The concentration of 4-hydroxyglucobrassin was higher in the leaves of first harvest crops. This response was due to this glucosinolate not being detected in the leaves of second harvest crops. Thus, the parent glucosinolate was altered between the first and second harvests in response to the abiotic stresses caused by harvesting. For annual garden rocket, there was an interaction between the harvest number and season for all glucosinolates measured. However, no clear response was observed between these factors. Higher concentrations of glucobrassicin and 4-methoxyglucobrassicin were measured for first harvest leaves when compared to the second harvest. This was due to the absence of detection of these glucosinolates in the leaves of second harvested plants; consequently higher total glucosinolate concentrations were measured for the first harvest winter (1224 µg kg(-1) FW) and summer (864 µg kg(-1) FW) crops. CONCLUSION The concentrations of individual glucosinolates vary greatly over typical pre- and post-harvest commercial conditions. The absence of 4-hydroxyglucobrassin for perennial wall rocket, and glucobrassicin and 4-methoxyglucobrassicin for annual garden rocket between harvests, illustrates that abiotic stress from harvesting has the capacity to alter the types of glucosinolates in leaves. Concentrations do not generally decline during a typical storage period, indicating that the potential benefits of these compounds are not lost during post-harvest storage.

Response of lettuce seedlings fertilized with fish effluent to Azospirillum brasilense inoculation

The continuous use of agrochemical inputs in modern agriculture for better crop productivity has resulted in unexpected environmental impact. This issue has raised public interest in exploring environmental friendly sustainable practices. In this study, three strains of Azospirillum brasilense (Sp7, Sp7-S and Sp245) were evaluated for their impacts on the growth of lettuce seedlings grown with fish effluent (FE) as a source of nutrients. Lettuce seeds were inoculated with these strains before sowing and at transplanting, and grown under greenhouse condition with natural light. Despite the existing indigenous microflora and low level of nutrients in the FE, the A. brasilense strains survived at populations ranging from 5 to 6 cfu g− 1 of roots and altered important agronomic traits, which led to growth enhancement. In particular, inoculated seedlings showed significant increase in the number of leaves, seedling height and root length. Chlorophyll and protein content were also improved, but only with Sp7 strain. However, the expression of pathogenesis-related protein, i.e., peroxidase, and level of endogenous indole-3-acetic acid increased by more than 50% in response to inoculation with the strains. Azospirillum inoculation also showed little or no adverse impact on the FE bacterial community indicating that it can be incorporated into a system that uses FE as a nutrient source, e.g., aquaponics. Thus, A. brasilense could be a valuable agent to help maximize the usefulness of FE or wastewater from freshwater aquaculture to further support plant growth.

THE GERMINATION OF PERENNIAL WALL ROCKET (DIPLOTAXIS TENUIFOLIA (L.) DC.) AND ANNUAL GARDEN ROCKET (ERUCA SATIVA MILL.) UNDER CONTROLLED TEMPERATURES

Abstract The germination characteristics of three cultivars of perennial wall rocket and annual garden rocket were assessed at constant and diurnal temperatures for ten days. The seeds were exposed to constant temperatures of 5, 10, 15, 20, 25, 30 and 35°C or diurnal temperatures of 24/10, 28/16 and 18/5°C, with a 12/12 h exposure of each regime. The diurnal temperatures were chosen to reflect the minimum and maximum ambient temperatures experienced in Ellis Lane, Australia; during the spring, summer and winter. The total germination percentage (TGP) of perennial wall rocket was the highest at 20 to 30°C, whereas the highest TGP occurred at 10 to 30°C for annual garden rocket. The daily germination speed (DGS) and germination value (GV) are two useful formulas used to express the germination characteristics of seeds that under certain conditions do not achieve ≥50% germination. For both species, there was a significant interaction between the cultivar and temperature for the DGS and GV at both constant and diurnal temperatures; illustrating that the commercial cultivars of these species germinate at different rates in response to different ambient temperatures. This has important implications for the commercial production of these species, as cultivars with high germination rates need to be chosen for different seasonal conditions. At diurnal temperatures, there was an interaction between the cultivar and temperature for perennial wall rocket, with the cvs. DT1 and DT2 having similar TGPs across all of the temperature regimes, whereas the cv. DT3 had lower TGPs across all of the regimes. There was no interaction between the cultivar and diurnal temperature for annual garden rocket; however, temperature did influence the TGP, with higher values at 24/10 and 18/5°C. The germination of the smaller seeds from the perennial species was found to be more dependent on temperature than the larger seeds from the annual species. This is likely due to differences in stored reserves and the influence of secondary dormancy in the respective species.

Variations in the Diurnal Flux of Greenhouse Gases from Soil and Optimizing the Sampling Protocol for Closed Static Chambers

There is no standardized method for the sampling of greenhouse gas fluxes from soil. Two methods are primarily used: closed dynamic chamber (CDC) and closed static chamber (CSC) systems. The most complex and costly are the CDC systems, which can sample gases in situ. However, the low-cost CSC systems are being increasingly used in which the gas samples are collected manually and analyzed off-site at a later date. Given their growing popularity, it is important to optimize the sampling procedure of the CSC systems to ensure that the measurements are both repeatable and representative. Samples from a commercial potato crop were collected in the morning and afternoon at 0, 15, 30, 60, 90, and 120 min after the chambers were closed, and the concentrations of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were determined using gas chromatography. The concentrations of CO2 and N2O inside chambers increased linearly over time, whereas the concentration of CH4 remained constant. The fluxes of CO2 and N2O from soil were greater in the afternoon than the morning, whereas the flux of CH4 was greater in the morning. For longer-term single-point soil flux monitoring using CSCs with a volume of 6.3 L, it is recommended that samples are collected in the morning at 0, 30, and 60 min after chambers are closed. This approach will ensure that the concentration of the gases are representative and will allow for a high level of repeatability and certainty in the results.

Germination Characteristics of Cucumber Influenced by Plant Growth–promoting Rhizobacteria

ABSTRACT Plant growth–promoting rhizobacteria (PGPR) represent a wide genera of rhizospheric bacteria that, when introduced in association with the host plant at optimum concentration, can enhance plant growth. Experiments were conducted to determine the germination response of cucumber (Cucumis sativus L.) to PGPR inoculation. Seed were inoculated with strains of Azospirillum brasilense Sp7, Sp7-S, and Sp245, Herbaspirillum seropedicea, and Burkholderia phytofirmans PsJNT. Germination was increased by up to 9% by strains of A. brasilense Sp7 and Sp245 and H. seropedicea. All PGPR strains consistently enhanced the germination vigor index; plants produced longer and heavier roots. These PGPR benefit cucumber germination.