Controlled Environment Studies Research Articles

Simulating winter wheat development response to temperature: Modifying Malo's exponential sine equation

Predicting crop developmental events is fundamental to simulation models and crop management decisions. Many approaches to predict developmental events have been developed, however, most only simulate the mean time for reaching a developmental event. An exponential sine equation developed by Malo [Malo, J.E., 2002. Modelling unimodal flowering phenology with exponential sine equation. Funct. Ecol. 16, 413–418] to predict flower number over time was modified to incorporate the response of crop development rate to temperature. The revised model (ExpSine model) uses the base, optimum, and maximum cardinal temperatures specific to a crop or genotype. Most model parameters were estimated from the literature, and four of the five model parameters have physiological significance. Model evaluation for winter wheat ( Triticum aestivum L.) was based on two controlled environment studies from the literature and two field experiments conducted in the North China Plain (NCP) and the Tibet Plateau (TPC). The r 2 for the modified temperature response function was 0.74 and 0.91 for two different experiments and compared very well (identical mean r 2's) to an existing function (Beta model) [Yin, X., Kropff, M.J., McLaren, G., Visperas, R.M., 1995. A nonlinear model for crop development rate as a function of temperature. Agric. Forest Meteorol. 77, 1–16]. Differences between observed and predicted flowering dates ranged from −2 to 3 days in the NCP and from −7 to 4 days on the TPC, with the mean percent error in both sites less than 1% and no apparent bias observed in the model. This modification of Malo's exponential sine equation expanded the predictive ability of the original equation to simulate phenology across a broader range of environments. The ExpSine model developed can be used as a phenological module in various crop or ecological simulation models.

Simulating Leaf Appearance in Rice

Most rice (Oryza sativa L.) simulation models assume that only temperature affects leaf appearance rate (LAR). This assumption ignores results from controlled environment studies that show that LAR in rice is not constant with time (calendar days) under constant temperature. The Streck model, which takes into account age effects on LAR, improved the prediction of leaf appearance in winter wheat (Triticum aestivum L.) cultivars compared with the Wang and Engel (WE) model and the phyllochron model but has not been evaluated in rice. The objective of this study was to adapt and evaluate the Streck model to simulate main stem LAR and leaf number in rice. A 4‐yr experiment with several sowing dates from 2003–2004 to 2006–2007 was performed at Santa Maria, RS, Brazil. Seven rice cultivars were used: IRGA 421, IRGA 420, IRGA 417, IRGA 416, BRS 7 (TAIM), BR‐IRGA 409, and EPAGRI 109. Plants were grown in 12‐L pots during the 4 yr, and in a paddy rice field during the 2006–2007 growing season. Coefficients necessary to run the Streck model, the WE model, and the phyllochron model were estimated with data from five sowing dates of the 2003–2004 growing season and the models were evaluated with independent data from the other three growing seasons. Predictions of the main stem leaf number, represented by the Haun Stage (HS), were better with the Streck model. The RMSE was 0.7, 1.0, and 1.8 leaves, for the Streck model, the WE model, and the phyllochron model, respectively.

Use of a crop model ensemble to quantify CO 2 stimulation of water-stressed and well-watered crops

Increased atmospheric concentrations of carbon dioxide (CO 2) will benefit the yield of most crops. Two free air CO 2 enrichment (FACE) meta-analyses have shown increases in yield of between 0 and 73% for C3 crops. Despite this large range, few crop modelling studies quantify the uncertainty inherent in the parameterisation of crop growth and development. We present a novel perturbed-parameter method of crop model simulation, which uses some constraints from observations, that does this. The model used is the groundnut (i.e. peanut; Arachis hypogaea L.) version of the general large-area model for annual crops (GLAM). The conclusions are of relevance to C3 crops in general. The increases in yield simulated by GLAM for doubled CO 2 were between 16 and 62%. The difference in mean percentage increase between well-watered and water-stressed simulations was 6.8. These results were compared to FACE and controlled environment studies, and to sensitivity tests on two other crop models of differing levels of complexity: CROPGRO, and the groundnut model of Hammer et al. [Hammer, G.L., Sinclair, T.R., Boote, K.J., Wright, G.C., Meinke, H., Bell, M.J., 1995. A peanut simulation model. I. Model development and testing. Agron. J. 87, 1085–1093]. The relationship between CO 2 and water stress in the experiments and in the models was examined. From a physiological perspective, water-stressed crops are expected to show greater CO 2 stimulation than well-watered crops. This expectation has been cited in literature. However, this result is not seen consistently in either the FACE studies or in the crop models. In contrast, leaf-level models of assimilation do consistently show this result. An analysis of the evidence from these models and from the data suggests that scale (canopy versus leaf), model calibration, and model complexity are factors in determining the sign and magnitude of the interaction between CO 2 and water stress. We conclude from our study that the statement that ‘water-stressed crops show greater CO 2 stimulation than well-watered crops’ cannot be held to be universally true. We also conclude, preliminarily, that the relationship between water stress and assimilation varies with scale. Accordingly, we provide some suggestions on how studies of a similar nature, using crop models of a range of complexity, could contribute further to understanding the roles of model calibration, model complexity and scale.

Germination Characteristics of the Dimorphic Seeds of Spreading Orach (Atriplex Patula)

Abstract Spreading orach is an annual weed that colonizes roadsides, field edges, and increasingly, no-till agricultural fields. It produces dimorphic seeds with different levels of physiological dormancy, but little is known about the germination ecology of the two seed types. Field and controlled-environment studies were conducted to determine seed responses to light and stratification, the pattern of seedling emergence in the field, and the effect of soil water content on the length of cold stratification required to break dormancy for each seed type. The large, brown seeds have three times the mass of the smaller, black seeds, primarily because of a larger embryo, but have a thinner seed coat. Germination of brown and black seeds in petri dishes was 98 and 90%, respectively, after stratification for 3 mo at 5 C, whereas germination of unstratified seeds was 19 and 12%, respectively. Light stimulated germination of both stratified and unstratified black seeds but did not increase germination in stratif...

Organic anions in the rhizosphere of Al-tolerant and Al-sensitive wheat lines grown in an acid soil in controlled and field environments

Several sampling methods were investigated for the quantification of organic anions in the rhizosphere of Al-tolerant (ET8) and Al-sensitive (ES8) wheat plants in soil systems. Controlled environment studies used anion exchange membranes to collect rhizosphere organic anions (from root tips and mature regions of nodal roots) from ET8 and ES8 plants at the 6-leaf stage in a glasshouse environment. Using the anion exchange membranes, a selection of organic anions were detected on the tips and mature regions of roots, with ET8 and ES8 having similar rhizosphere organic anion profiles. The field experiment used 2 established methods of organic anion collection: rhizosphere soil and root washings. The ET8 and ES8 wheat lines had similar levels of organic anions, including malate, in the rhizosphere (using soil shaken from roots and root washings) at 3 sampling times (4 and 6 leaves, and flowering). The rhizosphere organic anions differed significantly from the bulk soil, with the concentration and range of organic anions in the rhizosphere decreasing towards flowering, presumably due to physiological changes in plant and root growth. This study used several techniques to investigate organic anion exudation by roots, with organic anions detected using all techniques. However, technical limitations of these techniques were recognised: (i) the lack of simultaneous exposure of root tips to both the anion exchange membrane and the chemical stimulant, e.g. Al3+; and (ii) the inability to derive the origin of organic anions measured in rhizosphere soil and root washings. The challenge for future soil-based organic anion research is to identify the dominant stress that has triggered an exudation response (i.e. Al toxicity, P deficiency), and to clearly differentiate between plant- and microbial-derived contributions to exudation.

A detached fruit study on the post-inoculation activity of lime sulfur against brown rot of peach (Monilinia fructicola)

Fungicides with curative activity are important tools for disease management in stone fruits. Lime sulfur (LS) is the only fungicide registered for organic fruit production with demonstrated curative activity against apple scab, but such activity against Monilinia fructicola is unknown. In this study, the 6, 12, and 24 h post-infection activity of 1.5% lime sulfur (LS) against M. fructicola was investigated on two peach fruit cultivars (early- and mid-season cultivars, Coronet and Contender, respectively) at two maturity stages (commercially mature and immature fruit) in a wound-inoculation detached fruit study. Brown rot incidence, sporulating area, and production of conidia per fruit were higher on commercially mature fruit in all treatments as compared with immature fruit, and LS treatments showed consistent results for both cultivars tested. All three disease measurements were significantly lower (P=0.05) for the 6 and 12 h post-inoculation applications of LS compared with either the untreated or 24 h post-inoculation applications of LS, irrespective of fruit maturity stages or cultivar. Disease incidence was reduced from 98.5–100% in the control treatment to 9–12% in the 6 h post-inoculation application. Both the 6 and 12 h post-inoculation applications reduced sporulating area from 64–72% in the control treatment to 0.0–1.3%. Disease incidence was not significantly (P=0.05) different between the water-treated control and the 24 h post-inoculation treatment with LS, while percent sporulating area and number of conidia per fruit were significantly different (P=0.05). Our results show up to 12 h post-inoculation activity of LS on M. fructicola in controlled environment studies and indicate that LS has potential for post-infection brown rot control in organic stone fruit production. Additional keywords: disease management, organic fruit production, stone fruits.

Effect of Movements on the Electrodermal Response after a Startle Event

In this work the effect of quasi-stationary movements on the electrodermal activity (EDA) after a startle event has been investigated and evaluated. In previous EDA research there is a discrepancy between the use of controlled environment studies and daily life surveys. This paper aims to address this by expanding the knowledge about EDA in real life applications. A minimally obtrusive body-worn measurement device was designed and produced that simultaneously records EDA and finger movements. During this study, five subjects walked at different speeds and listened to startling sound events. The EDA response to these startle events was analyzed for different walking speeds using crosscorrelograms and cumulative frequency plots. The measured response to the startle event is consistent with the signal characteristics described in the literature. The results show that the faster a person is walking the more the signal property of the phasic part of the EDA is approaching a uniform distribution. However, even at a walking speed of 6 km/h the effect of the startle event is statistically still visible in the EDA (p < 0.05). The presented work offers a good understanding of the EDA while walking at different speeds. Although the artefacts evoked by walking cannot be determined directly, information on the movement can be useful. Depending on the walking speed a measurement about the reliability of peak detection could be introduced.

Field-based evaluation of vernalization requirement, photoperiod response and earliness per se in bread wheat ( Triticum aestivum L.)

Vernalization requirement, photoperiod response and earliness per se (EPS) of bread wheat cultivars are often determined using controlled environments. However, use of non-field conditions may reduce the applicability of results for predicting field performance as well as increase the cost of evaluations. This research was undertaken, therefore, to determine whether field experiments could replace controlled environment studies and provide accurate characterization of these three traits among winter wheat cultivars. Twenty-six cultivars were evaluated under field conditions using two natural photoperiod regimes (from different transplanting dates) and vernalization pre-treatments. Relative responses to vernalization (RRV GDD) and photoperiod (RRP GDD) were quantified using the reciprocal of thermal time to end of ear emergence, whereas earliness per se was estimated by calculating thermal time from seedling emergence until end of ear emergence for fully vernalized and lately planted material. An additional index based on final leaf numbers was also calculated to characterize response to vernalization (RRV FLN). To test whether the obtained indices have predictive power, results were compared with cultivar parameters estimated for the CSM-Cropsim-CERES-Wheat model Version 4.0.2.0. For vernalization requirement, RRV GDD was compared with the vernalization parameter P1V, for photoperiod (RRP GDD), with P1D, and for earliness per se, EPS was compared with the sum of the component phase durations. Allowing for variation in EPS in the calibration improved the relation between observed versus simulated data substantially: correlations of RRP GDD with P1D increased from r 2 = .34 ( p < .01), to .82 ( p < .001), and of RRV GDD with P1V, from r 2 = .88 ( p < .001), to .94 ( p < .001). In comparisons of observed versus simulated anthesis dates for independent field experiments, the estimated model coefficients resulted in an r 2 of .98 ( p < .001) and root mean square error of 1 d. Overall, the results indicated that combining planting dates with vernalization pre-treatments can permit reliable, quantitative characterization of vernalization requirement, photoperiod response and EPS of wheat cultivars. Furthermore, emphasize the need for further study to clarify aspects that determine EPS, including whether measured EPS varies with temperature or other factors.

Parameterization of the Phenological Development of Select Annual Weeds Under Noncropped Field Conditions

Barnyardgrass, common lambsquarters, redroot pigweed, and wild mustard are among the most common weeds in cropping systems throughout North America. Crop and weed competition models that predict phenological development across environments are useful research tools for advancing our knowledge of population dynamics or crop and weed competition. Phenological parameter estimates for such models require verification under field conditions. Field studies were conducted in 1999 and 2000 to determine growth and phenological development of these species under noncropped conditions to compare parameters developed previously from controlled environment studies. Weeds were planted on three separate planting dates in each year. Growth and phenological development were recorded. Number of leaves on the mainstem of all weed species, except common lambsquarters, was not affected by planting dates. Rate of leaf appearance described as a function of days after emergence ranged from 0.48 to 0.89, 0.10 to 0.31, 0.33 to 0.65, and 0.24 to 0.29 leaves d−1for common lambsquarters, barnyardgrass, redroot pigweed, and wild mustard, respectively. When expressed as a function of growing degree days (GDD), rate of leaf appearance for these species ranged from 0.04 to 0.05, 0.01 to 0.02, 0.04 to 0.07, and 0.02 to 0.03 leaves GDD−1, respectively. Planting date had differential effects on the rate of stem elongation and final plant height of each species in the 2 yr. Final plant biomass was also influenced by the time of planting; in general, weeds planted by mid-May had more biomass than those planted later. Parameters developed to describe phenological development under field conditions were comparable to those reported previously from controlled environment studies. We conclude that phenological parameters quantified under controlled environmental studies were comparable to those developed under field conditions for these weed species. Thus, either experimental method can be used to parameterize weed phenological development to initialize crop and weed competition models with reasonable confidence.

Seed Treatment Effects on Early-Season Pests of Corn and on Corn Growth and Yield in the Absence of Insect Pests

Second-generation neonicotinoid insecticides are being used to protect seeds and seedlings against injury by early season insects on a wide variety of crops. Seed-applied insecticides have recently been commercialized in the USA for early season insect control in corn. The systemic insecticides clothianidin (Poncho®) and thiamethoxam (Cruiser®) applied as seed treatments were evaluated for their effect on corn yield in the absence of noticeable insect attack over a three year period at a number of locations representing diverse growing environments in Kansas. No consistent effect on yield was detected for either compound at either high or low rates in locations where insects were not observed at damaging populations. Controlled-environment studies detected no differences in early season growth in the absence of insect pests in response to the same two rates of both insecticides. Both compounds were evaluated for their effect on early season corn pests and were found to be effective at high and low rates on wireworm, white grub, flea beetles and chinch bugs. Higher rates of both compounds were needed to reduce feeding damage caused by black cutworm. Seed treatments with either compound would be useful where early season pests are chronic problems.

An Intergenomic Reciprocal Translocation Associated with Oat Winter Hardiness Component Traits

The reciprocal intergenomic translocation between hexaploid oat (Avena sp.) chromosomes 7C and 17 (T7C‐17) has been associated with the division of cultivated oat into A. sativa L. and A. byzantina K. Koch species and differences in crown freezing tolerance and winter field survival. The objectives of this experiment were: (i) to validate the association of T7C‐17 with crown freezing tolerance and winter field survival in a population derived from a cross of the non‐winter‐hardy ‘Fulghum’ (non‐T7C‐17) with winter‐hardy ‘Norline’ (T7C‐17); (ii) to determine if preferential selection for T7C‐17 occurred during inbreeding; and (iii) to examine the association of T7C‐17 with the winter hardiness component traits heading date, plant height, and vernalization and photoperiod responses. Crown freezing tolerance and vernalization and photoperiod responses were evaluated in controlled environment studies. Heading date, plant height, and winter field survival were evaluated in field experiments during two seasons. The presence of the translocation was associated with greater crown freezing tolerance, winter field survival, and days to flowering. Translocation status was not associated with vernalization and photoperiod responses or plant height. The T7C‐17/non‐T7C‐17 segregation ratio was 2:1. These results confirmed the importance of T7C‐17 in conferring winter hardiness traits in winter oat and preferential selection for the translocation during inbreeding.

Impact of Diurnal Periodicity, Temperature, and Light on Sporulation of Bremia lactucae

ABSTRACT We evaluated direct and interactive effects of light quality and intensity, temperature and light, diurnal rhythms, and timing of high relative humidity during long day lengths on sporulation of Bremia lactucae, the causal agent of lettuce downy mildew, using inoculated lettuce seedlings and detached cotyledons. Suppression of sporulation by light was strongly dependent upon temperature and there was little suppression at </=10 degrees C. The most suppressive waveband was in the range from 400 to 450 nm, although a lesser effect of wavebands from 450 to 500 and 500 to 550 nm could be detected. At 15 degrees C, near the lower threshold for suppression of sporulation by light, a clear diurnal pattern of sporulation was observed independent of light and darkness. This diurnal rhythm potentially could interact with light and temperature to confound the results of controlled environment studies, and may be the controlling factor in timing of sporulation at low temperatures. Forecasting models that currently use sunrise and sunset to delimit periods conducive to sporulation can be adapted to short nights and extended twilight conditions by incorporating the effects reported herein. Additionally, models of sporulation could be adapted to better reflect a decrease or absence of the suppressive effect of light at <15 degrees C.

The expression of resistance in subterranean clover (Trifolium subterraneum) to races 1 and 2 ofKabatiella caulivorais affected by inoculum pressure but not by combinations of the two races

The performance of subterranean clover (Trifolium subterraneum) varieties in the field in the presence of the clover scorch pathogen, Kabatiella caulivora, can be highly variable in terms of the disease levels that develop. Although the influence of environmental conditions on development of this disease is documented, the influence of inoculum pressure or race combinations has not previously been investigated. Hence, separate controlled environment studies were undertaken to identify the effects of inoculum concentration and the effects of race combinations upon the expression of resistance to clover scorch disease in seedlings of seven subterranean clover varieties. In relation to the percentage of petioles with lesions following inoculation with different conidial concentrations of either race 1 or race 2 of K. caulivora, there was a significant effect of races (P<0.001), varieties (P<0.001) and of inoculum concentration (P<0.001) and also a significant interaction between races and varieties (P<0.001), and of inoculum concentration with varieties (P<0.05). Although levels of disease observed on the varieties tested were generally comparable to those observed in the field, the findings in relation to inoculum concentration may explain why the performance of some subterranean clover varieties in the field in the presence of the clover scorch pathogen can be highly variable, as evidenced by certain incidences of severe disease and/or collapses of field swards of Meteora and Karridale varieties in Western Australia. When inoculated with varying proportions of race 1 and race 2, there was a significant effect of race combination treatments (P<0.001), but there was no indication of any additive or interference effects between the two races when present together as a combination on the same plant in relation to host expression of resistance to each individual race. Together, these studies showed, for the first time, that expression of resistance to K. caulivora in subterranean clover is dependent on pathogen inoculum level but independent of the races present as mixtures. The implications of these studies are 3-fold. First, that variable expression of resistance in the field is related to inoculum pressure. Second, that seedling resistance to individual races should be able to be identified even where both races occur together in combination, eliminating the current expensive requirement of utilising a separate field screening site for each race. Third, these results indicate that while effective deployment of host resistance is particularly rewarding where cultural and/or chemical strategies are in place to keep the inoculum of the pathogen at manageable levels, it can also be rewarding even under high inoculum pressure.

Incidence-density relationship of pear scab (Venturia nashicola) on fruits and leaves

Lesion-count data on fruits/leaves from two regions of China and on leaves from controlled-environment studies were used to investigate incidence-density [incidence of leaves/fruits with lesion(s) and average number of lesions per leaf/fruit] and incidence-incidence [incidences of leaves and shoots with lesion(s)] relationships. Few of the datasets for the number of lesions per fruit/leaf could be fitted satisfactorily by a Poisson distribution. Three two-parameter distributions (negative binominal, Neyman type A and Polya-Aeppli) provided significantly better fit than the Poisson distribution, indicating a degree of aggregation in the number of lesions on a single leaf/fruit. However, many datasets could still not satisfactorily be fitted by these distributions. The dynamics of aggregation of lesions on leaves/fruits was well described by Taylor's power-law model. Regression models provided accurate predictions of the average number of lesions per leaf/fruit from the incidence of leaves or fruits with lesion(s). Nevertheless, the incidence-density relationship varied considerably between regions and between leaf and fruit scab. Field data also indicated that the number of scabbed leaves per shoot showed some degree of aggregation. The incidence of leaves with scab could be predicted accurately from the incidence of shoots with scab. The incidence-density relationships developed in this study could be used in making practical disease-management decisions when incidence of leaves with scab is less than 35%.

Hourly and seasonal variation in photosynthesis and stomatal conductance of soybean grown at future CO2 and ozone concentrations for 3 years under fully open‐air field conditions

It is anticipated that enrichment of the atmosphere with CO(2) will increase photosynthetic carbon assimilation in C3 plants. Analysis of controlled environment studies conducted to date indicates that plant growth at concentrations of carbon dioxide ([CO(2)]) anticipated for 2050 ( approximately 550 micromol mol(-1)) will stimulate leaf photosynthetic carbon assimilation (A) by 20 to 40%. Simultaneously, concentrations of tropospheric ozone ([O(3)]) are expected to increase by 2050, and growth in controlled environments at elevated [O(3)] significantly reduces A. However, the simultaneous effects of both increases on a major crop under open-air conditions have never been tested. Over three consecutive growing seasons > 4700 individual measurements of A, photosynthetic electron transport (J(PSII)) and stomatal conductance (g(s)) were measured on Glycine max (L.) Merr. (soybean). Experimental treatments used free-air gas concentration enrichment (FACE) technology in a fully replicated, factorial complete block design. The mean A in the control plots was 14.5 micromol m(-2) s(-1). At elevated [CO(2)], mean A was 24% higher and the treatment effect was statistically significant on 80% of days. There was a strong positive correlation between daytime maximum temperatures and mean daily integrated A at elevated [CO(2)], which accounted for much of the variation in CO(2) effect among days. The effect of elevated [CO(2)] on photosynthesis also tended to be greater under water stress conditions. The elevated [O(3)] treatment had no statistically significant effect on mean A, g(s) or J(PSII) on newly expanded leaves. Combined elevation of [CO(2)] and [O(3)] resulted in a slightly smaller increase in average A than when [CO(2)] alone was elevated, and was significantly greater than the control on 67% of days. Thus, the change in atmospheric composition predicted for the middle of this century will, based on the results of a 3 year open-air field experiment, have smaller effects on photosynthesis, g(s) and whole chain electron transport through photosystem II than predicted by the substantial literature on relevant controlled environment studies on soybean and likely most other C3 plants.

UV SUPPLEMENTATION FOR GROWTH REGULATION AND DISEASE CONTROL

The benefits of supplementary ultraviolet radiation (UVB: 280-320nm) in protected lettuce were investigated in controlled environment studies. Exposure to UV-B prior to inoculation with a conidial suspension of Bremia lactucae (lettuce downy mildew) led to significant reduction in the subsequent sporulation of the pathogen. In addition to disease control, UV treatments increased leaf thickness, reduced leaf area and increased leaf pigmentation in a red-leaved cultivar. Such changes in leaf area and thickness are important quality factors that would be expected to improve plant performance after transplantation into the field. The aim of further studies will be to test such findings in a commercial glasshouse environment.

Effects of exposure to below‐freezing temperatures, soil moisture content and nitrogen application on phyllochron in cool‐season grasses

AbstractAccumulated temperature may provide an indicator of the phenology of cool‐season grass to assist in the timing of management operations but its value is highly dependent on a reliable measure of phyllochron, i.e. time between the elongation of successive leaves. Field and controlled environment studies with Italian ryegrass (IRG, Lolium multiflorum Lam.) and tall fescue (TF, Festuca arundinacea Schreb.) measured leaf‐appearance responses to accumulated temperature with varying conditions of exposure to low temperatures, soil moisture content and nitrogen application. In a controlled environment, soil volumetric water contents below 20% (equivalent to moisture potentials greater than −0·1 MPa) or more frequent exposure to below‐freezing air temperatures increased the phyllochron values on the main tiller of IRG and TF. There was no evidence of an interaction between soil moisture content and cold exposure on phyllochron values. Nitrogen application resulted in only small reduction in phyllochron values. In field studies over 4 years the phyllochron values in IRG during the months of January to March were 184, 180, 180 and 167 accumulated °C above 0°C leaf−1, more than double the mean value measured in a controlled environment. A greater understanding of the impact of variable low temperatures and of soil moisture potential on the phyllochron is necessary before accumulated temperature can be used to indicate changes in development stages in grasses in different environments.

Photosynthesis, productivity, and yield of maize are not affected by open-air elevation of CO2 concentration in the absence of drought.

While increasing temperatures and altered soil moisture arising from climate change in the next 50 years are projected to decrease yield of food crops, elevated CO2 concentration ([CO2]) is predicted to enhance yield and offset these detrimental factors. However, C4 photosynthesis is usually saturated at current [CO2] and theoretically should not be stimulated under elevated [CO2]. Nevertheless, some controlled environment studies have reported direct stimulation of C4 photosynthesis and productivity, as well as physiological acclimation, under elevated [CO2]. To test if these effects occur in the open air and within the Corn Belt, maize (Zea mays) was grown in ambient [CO2] (376 micromol mol(-1)) and elevated [CO2] (550 micromol mol(-1)) using Free-Air Concentration Enrichment technology. The 2004 season had ideal growing conditions in which the crop did not experience water stress. In the absence of water stress, growth at elevated [CO2] did not stimulate photosynthesis, biomass, or yield. Nor was there any CO2 effect on the activity of key photosynthetic enzymes, or metabolic markers of carbon and nitrogen status. Stomatal conductance was lower (-34%) and soil moisture was higher (up to 31%), consistent with reduced crop water use. The results provide unique field evidence that photosynthesis and production of maize may be unaffected by rising [CO2] in the absence of drought. This suggests that rising [CO2] may not provide the full dividend to North American maize production anticipated in projections of future global food supply.

Potato and Human Exploration of Space: Some Observations from NASA-Sponsored Controlled Environment Studies

Future space exploration by humans will require reliable supplies of food, oxygen and clean water to sustain the expeditions. Potato is one of several crops being studied for such a “life support” role. Tests sponsored by the US National Aeronautics and Space Administration (NASA) confirmed the well-known short day tendencies for tuberisation, but also revealed that some cvs. (e.g., Norland, Denali and Russet Burbank) could tuberise well under continuous high light. Horticultural tests showed that plants grew well and tuberised readily using a nutrient film technique (NFT). CO2 enrichment studies with potato showed typical C3 responses in photosynthesis and yield, with maximum rates occurring near 1000 μmol mol−1. The highest tuber yields from these controlled environment studies reached 19.7 kg FM m−2 or equivalent to nearly 200 t ha−1. This equated to a productivity of 38 g m−2 DM m−2 day−1. Stand evapotranspiration (ET) rates ranged from 3.4 to 5.2 l m−2 day−1 throughout growth, while maximum ET rates for canopies could approach 10 l m−2 day−1. Harvest indices (tuber DM/total DM) typically ranged from 0.7 to 0.8, indicating that waste (inedible) biomass from potato would be less than that from many other crops. An experiment was conducted in 1995 on NASA’s Space Shuttle using excised potato leaves to study tuber formation at axillary buds during spaceflight. The results showed that tubers formed equally well in space as in the ground controls, indicating that reduced gravity should not be an impediment to tuberisation.

Interrelationship between spot blotch and common root rot in barley

Spot blotch and common root rot, caused by the fungal pathogen Cochliobolus sativus, are important barley diseases in many production areas of the world. The interrelationship between these two diseases was investigated in a series of controlled environment studies. Strong correlations were detected for barley reactions to both diseases. Large differences in disease reactions were observed among genotypes for each disease. No genotype was immune to both diseases, but the genotype WI 2291 was universally susceptible. Our results suggest that resistance to C. sativus in the subcrown internodes and leaves involve similar defence mechanisms. Such information would be useful to plant breeders because testing for spot blotch reaction requires less time than screening for common root rot resistance.