Controlled Environment Studies Research Articles

Identification of High-Temperature Tolerant Lentil (Lens culinaris Medik.) Genotypes through Leaf and Pollen Traits.

Rising temperatures are proving detrimental for various agricultural crops. Cool-season legumes such as lentil (Lens culunaris Medik.) are sensitive to even small increases in temperature during the reproductive stage, hence the need to explore the available germplasm for heat tolerance as well as its underlying mechanisms. In the present study, a set of 38 core lentil accessions were screened for heat stress tolerance by sowing 2 months later (first week of January; max/min temperature >32/20°C during the reproductive stage) than the recommended date of sowing (first week of November; max/min temperature <32/20°C during the reproductive stage). Screening revealed some promising heat-tolerant genotypes (IG2507, IG3263, IG3297, IG3312, IG3327, IG3546, IG3330, IG3745, IG4258, and FLIP2009) which can be used in a breeding program. Five heat-tolerant (HT) genotypes (IG2507, IG3263, IG3745, IG4258, and FLIP2009) and five heat-sensitive (HS) genotypes (IG2821, IG2849, IG4242, IG3973, IG3964) were selected from the screened germplasm and subjected to further analysis by growing them the following year under similar conditions to probe the mechanisms associated with heat tolerance. Comparative studies on reproductive function revealed significantly higher pollen germination, pollen viability, stigmatic function, ovular viability, pollen tube growth through the style, and pod set in HT genotypes under heat stress. Nodulation was remarkably higher (1.8–22-fold) in HT genotypes. Moreover, HT genotypes produced more sucrose in their leaves (65–73%) and anthers (35–78%) that HS genotypes, which was associated with superior reproductive function and nodulation. Exogenous supplementation of sucrose to in vitro-grown pollen grains, collected from heat-stressed plants, enhanced their germination ability. Assessment of the leaves of HT genotypes suggested significantly less damage to membranes (1.3–1.4-fold), photosynthetic function (1.14–1.17-fold) and cellular oxidizing ability (1.1–1.5-fold) than HS genotypes, which was linked to higher relative leaf water content (RLWC) and stomatal conductance (gS). Consequently, HT genotypes had less oxidative damage (measured as malondialdehyde and hydrogen peroxide concentration), coupled with a higher expression of antioxidants, especially those of the ascorbate–glutathione pathway. Controlled environment studies on contrasting genotypes further supported the impact of heat stress and differentiated the response of HT and HS genotypes to varying temperatures. Our studies indicated that temperatures >35/25°C were highly detrimental for growth and yield in lentil. While HT genotypes tolerated temperatures up to 40/30°C by producing fewer pods, the HS genotypes failed to do so even at 38/28°C. The findings attributed heat tolerance to superior pollen function and higher expression of leaf antioxidants.

New insights into the parametrization of temperature and light responses of mono - and sesquiterpene emissions from Aleppo pine and rosemary

Phytogenic emission of large volatile organic compounds (VOCs) such as monoterpenes (MTs) and sesquiterpenes (SQTs) are key precursors to the formation and growth of atmospheric particles. However, controlled environment studies to elucidate emission responses to temperature and light are still sparse. In this study, the volatile contents and emission responses of Aleppo pine and Rosemary have been investigated. These two common Mediterranean species store semivolatiles inside (resin ducts) and outside (trichomes) their foliage tissues respectively. Both species emitted mainly MTs with basal emission rates of around 5 (Rosemary) and 10 (pine) μg g−1 h−1 and SQTs about one order of magnitude lower. In Aleppo pine, two volatile sources could be clearly distinguished: 1) de-novo synthesized emission of (E)-β-ocimene and linalool, which accounted for about 70% of the total VOC release, were not found in foliar VOC extracts and expressed light dependency (LD) and temperature responses typical for enzyme driven emissions; and 2) storage-derived emissions of various MTs and SQTs whose emissions increased exponentially with temperature, showed no light dependency and were all present in leaf extracts. In Rosemary, all emitted MTs and SQTs including many oxygenated compounds, showed responses typical for stored volatiles and were all found in leaf extracts. The emissions of individual volatiles or volatile classes could be well described with the commonly applied empirical algorithms developed for LD or non LD emissions. However, the shapes of the temperature responses, and hence the deduced coefficient values, were significantly different between oxygenated and non-oxygenated compounds. They also differed between the storage-derived emissions of the two plant species, for individual VOCs or VOC classes. We address the possible reasons for this variation in temperature responses and argue that they are mostly due to molecular interactions along the species specific leaf-internal diffusion paths including the build-up of transient VOC pools and degradation.

Options for Management of Fusarium Wilt of Strawberry in California

ABSTRACTThe emergence of Fusarium wilt, caused by Fusarium oxysporum f. sp. fragariae, as a problem for strawberry production in California has been associated with delivery of fumigants to beds through drip-lines rather than flat-fumigation of an entire field. Our research shows that bed fumigation fails to eliminate propagules of the Fusarium wilt pathogen, which remain particularly abundant in bed shoulders at a depth of 30 cm. Controlled environment studies confirmed that inoculum at this depth could cause disease. Screening of currently grown strawberry cultivars documented a wide range of susceptibilities to Fusarium wilt, with some being highly resistant.

Ion concentrations in seagrass: A comparison of results from field and controlled-environment studies

Osmoregulation is essential for the survival of seagrasses in marine and hypersaline environments. The aim of this study was to examine ion concentrations of four seagrass species (Posidonia australis, P. sinuosa, Amphibolis antarctica and A. griffithii) after exposure to salinity changes. Plant fragments were placed in a series of aquaria at marine salinity (35) and, after one week of acclimation, exposed for 7 days to salinities between 20 and 70. Cl−, Na+ and total ion concentration increased with salinity in leaf tissue of the four seagrasses species. These results were compared with those of P. australis and A. antarctica samples collected at three locations at Shark Bay, Western Australia where higher salinities occurred, ranging from 46 to 51. Concentrations of K+ and Ca+2 were higher in seagrass tissues from Shark Bay than in those in aquarium trials. Cl−, Na+ and total ions in P. australis and A. antarctica from Shark Bay were lowest at the highest salinity location. The K+/Na+ ratio in the aquarium trials (under ambient conditions) was in the following order: A. antarctica = A. griffithii > P. australis > P. sinuosa and Ca+2/Na+ ratio was: A. antarctica = A. griffithii > P. sinuosa > P. australis. This species order indicates a physiological capacity to tolerate variation in salinity. Furthermore, these ratios were higher in the locality with highest salinity in Shark Bay, indicating acclimation and adaptation of ion concentrations to the salinity regime in the environment.

Will changes in phenology track climate change? A study of growth initiation timing in coast Douglas-fir.

Under climate change, the reduction of frost risk, onset of warm temperatures and depletion of soil moisture are all likely to occur earlier in the year in many temperate regions. The resilience of tree species will depend on their ability to track these changes in climate with shifts in phenology that lead to earlier growth initiation in the spring. Exposure to warm temperatures ('forcing') typically triggers growth initiation, but many trees also require exposure to cool temperatures ('chilling') while dormant to readily initiate growth in the spring. If warming increases forcing and decreases chilling, climate change could maintain, advance or delay growth initiation phenology relative to the onset of favorable conditions. We modeled the timing of height- and diameter-growth initiation in coast Douglas-fir (an ecologically and economically vital tree in western North America) to determine whether changes in phenology are likely to track changes in climate using data from field-based and controlled-environment studies, which included conditions warmer than those currently experienced in the tree's range. For high latitude and elevation portions of the tree's range, our models predicted that warming will lead to earlier growth initiation and allow trees to track changes in the onset of the warm but still moist conditions that favor growth, generally without substantially greater exposure to frost. In contrast, toward lower latitude and elevation range limits, the models predicted that warming will lead to delayed growth initiation relative to changes in climate due to reduced chilling, with trees failing to capture favorable conditions in the earlier parts of the spring. This maladaptive response to climate change was more prevalent for diameter-growth initiation than height-growth initiation. The decoupling of growth initiation with the onset of favorable climatic conditions could reduce the resilience of coast Douglas-fir to climate change at the warm edges of its distribution.

Application of woody biochar and woody mulch to mitigate nitrous oxide emissions from a poultry litter-amended soil in the subtropics

Numerous controlled-environment studies have found significant reductions in soil nitrous oxide (N2O) emissions following amendment of soil with woody biochar, but there is limited evidence to support these findings under field conditions. We evaluated N2O emissions from soils amended with 1) 5tha−1 surface applied poultry litter; 2) 5tha−1 incorporated poultry litter; 3) 5tha−1 poultry litter+11tha−1 woody biochar; 4) 5tha−1 poultry litter+10tha−1 woody mulch; 5) 4tha−1 poultry litter biochar+11tha−1 woody biochar, in a coppiced Melaleuca plantation over two years. Melaleuca biomass, total soil carbon (C) and nitrogen (N) and soil C fractions did not differ among treatments 12 months after amendment. Woody mulch applied with poultry litter resulted in significantly lower N2O emissions compared to the incorporated and surface- applied poultry litter in the second season, but the addition of woody biochar had no significant impact on cumulative N2O emissions. However, N2O emissions per unit of N applied were significantly (P<0.05) lower in the woody mulch and woody biochar treatments compared to poultry litter alone in the second season. In both seasons, cumulative N2O emission and N2O emissions per unit of N applied were significantly lower in the poultry litter biochar+woody biochar treatment, supporting the notion that pyrolysis of poultry litter is a management practice that could substantially reduce N2O emissions from the agricultural sector.

Heat Stress at Reproductive Stage Disrupts Leaf Carbohydrate Metabolism, Impairs Reproductive Function, and Severely Reduces Seed Yield in Lentil

ABSTRACTRising temperatures or global warming will be detrimental for various crops. Moreover, because of increasing demand for lentil (Lens culinaris L.) grains, there is a need to broaden the adaptation of this crop into warmer climes. Hence, a study was conducted to evaluate the effects of high temperatures (>32/20oC) during reproductive growth on performance of lentil and to probe the mechanisms associated with reproductive failures. Three lentil genotypes, viz., LL699, LL931, and LL1122, were grown in pots at two sowing dates: (1) the normal sowing time (NS) in November so that day/night temperatures during the reproductive stage were below 32/20°C; and (2) late-sown (LS) in February so that temperatures during the reproductive stage were above 32/20°C. The plants were fully irrigated during both the sowing situations. In LS plants, the phenology was accelerated, leading to substantial reduction in biomass, flowers, and pods, accompanied by marked shortening of flowering period and podding duration, causing decreased seed yield. At the peak flowering stage (average temp. >32/23oC), the leaves of the LS plants had significantly lower relative leaf water content and lower stomatal conductance than NS plants at the same stage, indicating that the late sowing induced both water stress and heat stress. In LS plants, reproductive function was markedly reduced in all genotypes, causing increased pod abortion. The leaves of LS plants showed increased damage to membranes, chlorosis, decreased photochemical efficiency, with an associated reduction in sucrose synthesis and increase in its hydrolysis, compared with the NS plants. Heat stress, in combination with intermittent water stress during the reproductive phase in the LS plants, was extremely detrimental for all three lentil genotypes, with only minor differences among them. Controlled-environment studies, where the plants were subjected to high temperatures (33/15°C, 35/20°C) during reproductive growth, also validated the detrimental effects of heat stress on studied traits, similar to outdoor conditions.

Capturing heat stress induced variability in spikelet sterility using panicle, leaf and air temperature under field conditions

Heat stress induced increase in spikelet sterility is often correlated with prevailing air temperature during anthesis. However, plant tissue temperature can be different from air temperature, depending on transpiration cooling which is a function of relative humidity (RH). Controlled environment studies involving heat stress are generally conducted at targeted RH, hence excluding the dynamics associated with this factor. Using 81 diverse indica cultivars over three years (wet season-2012, dry season-2013 and 2014), flag leaf temperature (FLT), panicle temperature (PT) and air temperature (AT) were measured during flowering under field conditions. On average the FLT and PT were 10.4 and 8.7°C lower than AT during the wet season and were 9.9 and 8.0°C lower when averaged across all three seasons. Spikelet sterility in dry seasons ranged between 1.6 and 67% compared to <1 and 35.5% during the wet season. Spikelet sterility was significantly correlated with PT (r=0.50; p<0.01) and FLT (r=0.55; p<0.01), compared with a weaker relationship with AT (r=0.23; p<0.05) among the tested 81 cultivars, pooled across both 2013 and 2014 dry seasons. By employing an unbiased Z score approach, cultivars with (i) consistent and contrasting for sterility percentage and (ii) phenology (duration from seeding till 50% flowering) based on flowering date confirmed the strong relationship between FLT or PT with spikelet sterility compared to AT. In conclusion, we recommend using either PT or FLT (tissue temperatures) instead of AT for future field based heat stress phenotyping. Where direct PT measurements are not available, mechanistic and empirical models can be used to derive PT or FLT from weather station data, or remotely sensed canopy temperature might be used as a proxy in large scale phenotyping experiments.

Leaf appearance of annual clovers responds to photoperiod at emergence

Abstract Leaf appearance rate and time to canopy expansion of four annual clover species (arrowleaf, balansa, gland and Persian) were quantified in field and controlled environment studies. Crops sown in autumn, which experienced shortening daylengths at emergence, had a slower rate of leaf production and consequently took a longer time to initiate branching, than spring-sown crops. When autumn-sown ‘Bolta’ balansa clover emerged on the shortest day in winter (21 June), the rate of leaf appearance was lengthened by 4 °C d/leaf/h. When the same species emerged after the shortest day, into an increasing photoperiod, the phyllochron was shortened by 5 °C d/leaf/h. This influence of photoperiod on the phyllochron consequently altered the time to axillary leaf production (branching). Throughout all sowing dates, phyllochron was the fastest for ‘Prima’ gland (33–91 °C d/leaf) and slowest for ‘Cefalu’ arrowleaf (53–116 °C d/leaf) clovers. ‘Bolta’ balansa was 44–82 °C d/leaf and ‘Mihi’ Persian 61–93 °C d/leaf. The response of phyllochron to photoperiod suggests these annual clovers should be sown in late summer or early autumn to initiate axillary leaf production as soon as possible to ensure maximize dry matter for early spring.

Screening for new accumulator plants in potential hazards elements polluted soil surrounding Peruvian mine tailings

Tailings usually provide an unfavorable substrate for plant growth because of their multi-stress environment. Plants growing on naturally metal-enriched soils are of particular interest in this perspective, since they are genetically tolerant to high metal concentrations and have an excellent adaptation to extreme conditions. Soil and plant samples were taken in Peru, at a polymetallic mine (mainly Ag, Pb and Cu) in Cajamarca Province, Hualgayoc district. Top soils (0–20cm) were analyzed for physical and chemical properties by standard methods. Total As, Cu, Pb and Zn concentrations in top soils were determined by ICP–OES. Similar metals in plants were analyzed separately (aerial and root system) by ICP–MS. Translocation Factor (TF) and Shoot Accumulation Factor (SAF) were determined to assess the tolerance strategies developed by these species and to evaluate their potential for phytoremediation purposes. The non-polluted soils had near neutral pH (6.8±0.1), a great content of organic carbon (42±4.0gkg−1) and a silt loamy texture. Soil and plant samples were taken at four locations (CA1, CA2, CA3, CA4) as well as the local reference topsoil (CA0). The range of total soil values in mg kg−1 is as follows: As 280–1029; Cu 256–2070; Pb 3992–16,060 and Zn 11,550–28,059, respectively. Unusual elevated concentrations of Pb (over 1000mgkg−1) and TF greater than one were detected in shoots of six different plants species (Ageratina sp., Achyrocline alata (Kunth) DC., Cortaderia hapalotricha Pilg., Epilobium denticulatum Ruiz & Pav., Taraxacum officinale Weber and Trifolium repens Walter). Ageratina sp and E. denticulatum also showed elevated concentrations of Zn (over 10,000mgkg−1) and TF greater than one in some studied locations. However, the SAF was smaller than one. Controlled-environment studies must be performed to definitively confirm the Pb hyperaccumulation character of the cited plant species.

Temperature extremes: Effect on plant growth and development

Temperature is a primary factor affecting the rate of plant development. Warmer temperatures expected with climate change and the potential for more extreme temperature events will impact plant productivity. Pollination is one of the most sensitive phenological stages to temperature extremes across all species and during this developmental stage temperature extremes would greatly affect production. Few adaptation strategies are available to cope with temperature extremes at this developmental stage other than to select for plants which shed pollen during the cooler periods of the day or are indeterminate so flowering occurs over a longer period of the growing season. In controlled environment studies, warm temperatures increased the rate of phenological development; however, there was no effect on leaf area or vegetative biomass compared to normal temperatures. The major impact of warmer temperatures was during the reproductive stage of development and in all cases grain yield in maize was significantly reduced by as much as 80−90% from a normal temperature regime. Temperature effects are increased by water deficits and excess soil water demonstrating that understanding the interaction of temperature and water will be needed to develop more effective adaptation strategies to offset the impacts of greater temperature extreme events associated with a changing climate.

Impact of heat stress on crop yield—on the importance of considering canopy temperature

Increasing crop productivity while simultaneously reducing the environmental footprint of crop production is considered a major challenge for the coming decades. Even short episodes of heat stress can reduce crop yield considerably causing low resource use efficiency. Studies on the impact of heat stress on crop yields over larger regions generally rely on temperatures measured by standard weather stations at 2 m height. Canopy temperatures measured in this study in field plots of rye were up to 7 °C higher than air temperature measured at typical weather station height with the differences in temperatures controlled by soil moisture contents. Relationships between heat stress and grain number derived from controlled environment studies were only confirmed under field conditions when canopy temperature was used to calculate stress thermal time. By using hourly mean temperatures measured by 78 weather stations located across Germany for the period 1994–2009 it is estimated, that mean yield declines in wheat due to heat stress during flowering were 0.7% when temperatures are measured at 2 m height, but yield declines increase to 22% for temperatures measured at the ground. These results suggest that canopy temperature should be simulated or estimated to reduce uncertainty in assessing heat stress impacts on crop yield.

Effect of short-term heat stress prior to flowering and early grain set on the grain yield of wheat

Short periods of heat stress in spring under Mediterranean climate can have large effects on crop yields. Most studies on heat stress have focused on crop responses to extended periods of high temperature under controlled environment conditions. There is limited information on the effects of short periods of heat stress on the yield of wheat. Therefore, field and controlled environment studies were undertaken to determine the effects of short-term heat stress on flag leaf senescence, as well as grain yield and its components. Wheat genotypes were exposed to heat stress for a single-day at two different stages: (H1) near flowering or green anther stage and (H2) early grain set or 7–10 days after anthesis (DAA) in 2009 and 2010. Heat treatment was applied in the field in a portable purpose-built heat chamber in which the temperature was steadily increased to a maximum of 35°C, which was maintained for 3h before being allowed to steadily decrease to the ambient temperature, like a typical spring heat event. Similar to the field studies, wheat genotypes were also exposed to a single-day heat event (35°C maximum) in the controlled environment (CE) study. This single-day heat stress event caused a significant reduction in grain yield and yield components in both years. Heat stress (H1 or H2) accelerated the rate of loss of flag leaf chlorophyll content. A higher rate of senescence in 2009, which was warmer and drier than 2010, was associated with greater yield loss. Reduction in grain yield among the genotypes was negatively correlated (r=−0.79; p<0.001) with the rate of flag leaf senescence. Heat stress reduced post-heading duration and grain yield across genotypes and heat stress treatments was strongly correlated (r=0.80; p<0.001 in 2009 and r=0.82; p<0.001 in 2010) with post-heading duration. There was also a significant (p<0.001) positive correlation between wheat grain yield and grain number m−2 (2009: r=0.79 and 2010: r=0.70) and wheat grain yield and individual grain mass (IGM) at harvest (r=0.70 in 2009 and r=0.82 in 2010). Standardized partial regression coefficient (b) showed that of the two yield components the contribution of grain number (b=0.786) to the grain yield was higher than IGM (b=0.435) in 2009. In contrast, IGM (b=0.665) appeared to be a stronger contributor to the grain yield than grain number (b=0.443) in 2010. Grain yield loss of different wheat genotypes was strongly correlated (r=0.91; p<0.001) between the field and CE. The results of these studies showed that under field and CE conditions, Janz was consistently the most sensitive genotype to heat stress. In contrast, CM9-6Y, CM9-4Y and Krichauff appeared to be most tolerant to heat stress. Averaged over the two growing seasons and heat stress treatments, the reduction in grain yield was greater in Janz (25%) than in CM9-6Y and CM9-4Y (13% each), followed by Krichauff (16%) and Excalibur (18%). It could be suggested that early headed wheat genotypes with slower rate of leaf senescence after heat exposure and longer post-heading duration could be more tolerant to heat stress.

What's ‘cool’ in the world of green façades? How plant choice influences the cooling properties of green walls

Green walls provide an option for reducing the thermal load on buildings, reducing the requirement for mechanised air conditioning and helping to mitigate urban heat islands. The range and extent of benefits can vary with green wall typology. This research investigated green façades utilising wall shrubs and climbing plants to reduce air temperature adjacent to, and surface temperatures of, brick walls. Artificial wall sections were used to provide replicated data sets in both outdoor and controlled environmental conditions. During periods of high solar irradiance outdoors, the presence of live Prunus laurocerasus plants placed against walls significantly reduced air and surface temperatures compared to blank walls, but also in comparison to excised (non-transpiring) plant sections. Largest temperature differentials were recorded mid-late afternoon, where air adjacent to vegetated walls was 3 °C cooler than non-vegetated walls. Prunus also provided significant wall cooling in controlled environment studies, but was intermediate in its surface cooling capacity (6.3 °C) compared to other species; Stachys and Hedera providing >7.0 °C cooling. When evaluated on a per leaf area basis, however, other species demonstrated greater cooling potential with Fuchsia, Jasminum and Lonicera out-performing others. Not only was it evident that different species varied in their cooling capacity, but that the mechanisms for providing wall cooling varied between species. Fuchsia promoted evapo-transpiration cooling, whereas shade cooling was more important in Jasminum and Lonicera. Plant physiology and leaf area/morphology should be considered when selecting species to maximise cooling in green wall applications.

High level resistance to Pseudocercosporella capsellae offers new opportunities to deploy host resistance to effectively manage white leaf spot disease across major cruciferous crops

Field and controlled environment studies were undertaken to define the range and extent of available host resistances to Pseudocercosporella capsellae (white leaf spot) across diverse oilseed, forage and vegetable crucifers, including some wild and/or weedy species, and also within and/or derived from Brassica carinata. In each experiment, there was a wide range in host response from high resistance to high susceptibility as assessed by four disease parameters, viz. in the field for: (i) Area Under Disease Progress Curve (AUDPC) for percent leaves diseased with values ranging from 0 to 375.5; (ii) Percent Leaf Collapse Index (%LCI) for leaf collapse due to disease with values ranging from 0 to 23.0; and (iii), Percent Pod Area Disease Index (%PADI) for pod area affected with values ranging from 0 to 52.1; and (iv) under controlled environmental conditions for Percent Cotyledon Disease Index (%CDI) for cotyledon lesion size with values ranging from 0 to 27.5. At the Crawley field site, B. carinata ATC 94129 was the most resistant genotype with AUDPC = 1.2, followed by Crambe abyssinica (AUDPC 8.7), Eruca sativa Eruc-01 (AUDPC 19.3) and E. vesicaria Yellow rocket (AUDPC 19.4). B. carinata ATC 94129 and B. oleracea var. capitata had the least leaf collapse, with %LCI = 0.2. At the Shenton Park field site, 21 genotypes of B. carinata and B. oleracea var. acephala Tuscan kale showed total resistance, all with AUDPC values of 0. Of the B. napus genotypes carrying one or more B. carinata B genome introgressions, genotypes NC8 (AUDPC 23.0) and NC9-1 (AUDPC 26.2) were the most resistant. Genotypes as assessed on these disease criteria as having high level resistance generally showed no pod infection; in contrast to %PADI values up to 52 on the most susceptible genotypes. Under controlled environmental conditions, the most resistant genotype was B. carinata ATC 94129 with %CDI values of 0 and 0.2, respectively, across two experiments, along with B. napus genotypes Zhongyou 821 and Hyola 42, with a %CDI value of 0 in one of the two experiments. There was a high degree of correlation both within individual experiments across the different disease parameters and also between field and controlled environment experiments. Within both B. napus and B. juncea genotypes tested, the most resistant genotypes were from China, the most susceptible from India, with those from Australia intermediate.

Feature: Improving our knowledge of drought‐induced forest mortality through experiments, observations, and modeling

Feature: Improving our knowledge of drought‐induced forest mortality through experiments, observations, and modeling

Effects of Temperature and Wetness Duration on the Sporulation Rate of Phomopsis viticola on Infected Grape Canes.

Controlled-environment studies were conducted to examine effects of temperature (T) and wetness duration (W) on the sporulation rate of Phomopsis viticola on infected grape canes and to determine effects of interrupted wetness duration (IWD) on sporulation. A split-plot design was used to determine T and W effects, with T (5, 12, 15, 18, 20, 22, 25, 28, and 35°C) as the whole-plot and W (11, 23, 35, 47, and 71 h) as the subplot. Linear and nonlinear mixed models were fitted to the data. Lower and upper limits of sporulation were estimated to be 4 and 36°C, respectively, based on the modeling results, optimum sporulation was near 21°C, and sporulation increased monotonically with increasing wetness duration. Of the examined models, a generalization of the Analytis Beta model fit the data best, based on a collection of goodness-of-fit statistical criteria. To determine effects of IWD, a split-plot was used, with T (12, 15, and 20°C) as the whole-plot and IWD (0, 2, 4, 8, 12, and 24 h) as the subplot. Generally, sporulation declined with increasing IWD. An IWD of 8 h or more resulted in significantly and substantially less sporulation compared to the control (0 h IWD) (P < 0.01). Temporal patterns of spore density in the field were determined using a repeated-measures design, in which spore density and environmental data were measured in the vineyard during and following individual rain events over 3 years. The developed model from the controlled-environment study, coupled with a time-of-season weight function and a dispersal index (based on total rain per rain episode), predicted the trend in spore density over time reasonably well, although the total magnitude of spore density could not be predicted because the density of lesions was not known. Results can be used for improving the accuracy of a disease warning system that currently only considers infection of grapes by P. viticola.

Effect of short-term heat stress prior to flowering and at early grain set on the utilization of water-soluble carbohydrate by wheat genotypes

In Mediterranean environments, cereal crops are often exposed to short periods of elevated temperatures in spring when crops are approaching flowering and grain filling. Stem water-soluble carbohydrate (WSC) could be an important carbon bank for supporting grain filling in wheat especially when carbon assimilation is hampered by heat stress. However, there is relatively little information available in the literature on the effects of short periods of heat stress on grain growth and the importance of WSC in mitigating the effects of heat stress. Therefore, field and controlled environment studies were undertaken to determine the effects of short-term heat stress on the peduncle WSC content and its contribution to grain size of wheat in the field. Wheat genotypes were exposed to heat stress on a single-day at two different stages: (H1) near flowering or green anther stage and (H2) early grain set or 7–10 days after anthesis (DAA). On each occasion crops were enclosed in a portable heat chamber and the temperature was gradually increased to a maximum of 35°C. This single day heat stress event caused a significant reduction in individual grain mass (IGM) and grain number in both years. There was no discernible change in IGM until 14 days postanthesis, after which time grain growth in the heat-stressed plants was reduced. On average, as compared to the unheated control, the reductions in IGM in wheat genotypes ranged from 10 to 25%. The maximum WSC content was reduced by heat stress in all wheat genotypes. Heat stress (average of H1 and H2) reduced peduncle WSC content by 26% and mobilized WSC content by 15% across all studies. Mobilization of peduncle WSC content was also significantly reduced by the heat stress treatments and mobilization appeared to start at 21 days postanthesis when the grain was about one third of the final mass. IGM of wheat genotypes with higher maximum peduncle WSC content showed lower sensitivity to heat stress in both years of this study (H1: r=−0.82; p<0.001 and H2: r=−0.84; p<0.001). Over both seasons, heat stress treatments (H1, H2) and all genotypes, greater mobilized WSC was associated with increased grain size (r=0.70; p<0.01). It could be argued that selection of wheat genotypes with higher stem WSC reserves and greater mobilization of WSC could be used to buffer grain growth and development under heat stress conditions, which are a common occurrence in the Australian wheat belt.

Soil conditions and cereal root system architecture: review and considerations for linking Darwin and Weaver

Charles Darwin founded root system architecture research in 1880 when he described a root bending with gravity. Curving, elongating, and branching are the three cellular processes in roots that underlie root architecture. Together they determine the distribution of roots through soil and time, and hence the plants' access to water and nutrients, and anchorage. Most knowledge of these cellular processes comes from seedlings of the model dicotyledon, Arabidopsis, grown in soil-less conditions with single treatments. Root systems in the field, however, face multiple stimuli that interact with the plant genetics to result in the root system architecture. Here we review how soil conditions influence root system architecture; focusing on cereals. Cereals provide half of human calories, and their root systems differ from those of dicotyledons. We find that few controlled-environment studies combine more than one soil stimulus and, those that do, highlight the complexity of responses. Most studies are conducted on seedling roots; those on adult roots generally show low correlations to seedling studies. Few field studies report root and soil conditions. Until technologies are available to track root architecture in the field, soil analyses combined with knowledge of the effects of factors on elongation and gravitropism could be ranked to better predict the interaction between genetics and environment (G×E) for a given crop. Understanding how soil conditions regulate root architecture can be effectively used to design soil management and plant genetics that best exploit synergies from G×E of roots.

Microorganisms Associated with Valencia Peanut Affected by Pod Rot in New Mexico

Abstract Pod rot of peanut is a disease that occurs worldwide. Soilborne pathogens typically causing pod rot include Rhizoctonia solani, Sclerotium rolfsii, and Pythium spp. Although pod rot is known to occur in New Mexico, no etiological study has been conducted on this disease. In 2005 and 2006, 14 Valencia peanut fields were surveyed in eastern New Mexico where the majority of Valencia peanut is produced. The primary focus of the study was to isolate and identify microorganisms associated with pod rot. The secondary focus of the study was to characterize microorganisms from roots and stems from the same plants selected for pod rot assessment. Peanut plants were collected and processed for isolation of microorganisms by plating seeds, pieces of hull, root, and stem on acidified potato dextrose agar. In both years, the average incidence of pods with hull discoloration or pod rot symptoms varied from 55–60 to over 90%, and disease severity ranged from 5 to over 90% across all fields surveyed. A diverse group of microorganisms representing more than 10 fungal and Oomycete genera were recovered from all plant part tissues, with R. solani as the most predominantly isolated mycelial microorganism. Rhizoctonia solani was found in all fields with average frequency of isolation from approximately 20 to 27% for pod tissue, 19 to 36% for root, and 20 to 27% for stem. In controlled-environment studies, all isolates of R. solani from different plant parts were shown to be pathogenic to Valencia peanut. This etiological study is the first in New Mexico to provide an insight into microorganisms associated with peanut affected by pod rot. Breeding Valencia peanuts for resistance to Rhizoctonia pod rot should be a priority.