Demographic and Biomass Production Consequences of Inundative Treatment of Cirsium arvense with Sclerotinia sclerotiorum

The adventitious shoots in three populations of Cirsium arvense in sheep-grazed pastures were treated in October (spring) 1991 with a mycelium/wheat formulation of Sclerotinia sclerotiorum and the fates of mapped shoots were followed over the growing season. In untreated plots, deaths through natural causes were compensated for by births (emergence of new shoots above the soil) throughout the growing season, but, on plots treated with S. sclerotiorum, deaths from the induced disease exceeded births for 35 days following treatment, causing the shoot population to decline markedly. Disease-induced deaths occurred only among shoots present at the time of treatment; there was no evidence of transfer of the pathogen to shoots emerging after the treatment was applied. A life-table analysis showed that only 8% of the adventitious shoots emerging during the growing season survived to seeding on treated plots, compared with 28% on the untreated plots; most mortalities occurred in shoots at the vegetative stage of development. The dry mass of propagative roots in autumn was reduced to 35% of that on the untreated plots by the pathogen and the density of shoots emerging the following spring was reduced to a similar extent. The results of this study indicate that S. sclerotiorum has potential as a mycoherbicide for C. arvense in sheep-grazed pasture in New Zealand.     

A Comparison of Auxotrophic and Wild Strains of Sclerotinia sclerotiorum Used as a Mycoherbicide Against Californian Thistle ( Cirsium arvense )

Two auxotrophic mutant strains of Sclerotinia sclerotiorum were tested in the greenhouse for pathogenicity on Cirsium arvense (Californian thistle) with and without amino acid amendments. An arginine auxotrophic mutant, with an amendment of the amino acid, followed an identical disease progress curve to that of the wild strain of the pathogen from which it was derived. However, when deprived of the amino acid amendment it was still highly pathogenic. A leucine auxotrophic mutant demonstrated poor pathogenicity without a leucine amendment, but improved pathogenicity with the addition of the amino acid. However, both of these treatments were inferior to the two wild strains tested and the arginine auxotroph with and without amendments. A field experiment was conducted on C. arvense stems in permanent pasture to compare the pathogenicity of amended auxotrophic strains and wild strains of S. sclerotiorum applied as a granule in a wheat-based carrier. The two wild strains gave significant reductions in thistle cover within 3 months of treatment, and subsequent reductions in thistle stem height and density during the following season. There was no evidence that the auxotrophic strains reduced thistle cover in the season the treatments were applied, but they did reduce subsequent stem density in the following spring. To determine disease carry-over associated with the wild and auxotrophic strains of the pathogen, rape was planted into subplots over the next three consecutive seasons. Despite substantial populations of sclerotia being present in the soil, especially in the first season after treatment of the thistles, no disease of rape caused by S. sclerotiorum was detected over the three seasons in any of the plots. Sclerotium populations of S. sclerotiorum in the soil declined by over 50% between 20 and 32 months after treatment, but there was no decline over the subsequent 12 months. The trial demonstrated that the auxotrophic strains were less field fit compared with the wild strains and that the presence of inoculum and a susceptible host to S. sclerotiorum were not the only prerequisites for disease development. It was concluded that use of a trap crop following treatment is not a suitable method for determining the risk of using this pathogen as a mycoherbicide in pasture.     

Field Note: Comparative Efficacy of A Woody Evapotranspiration Landfill Cover Following the Removal of Aboveground Biomass

Woody vegetation cultivated for moisture management on evapotranspiration (ET) landfill covers could potentially serve a secondary function as a biomass crop. However, research is required to evaluate the extent to which trees could be harvested from ET covers without significantly impacting their moisture management function. This study investigated the drainage through a six-year-old, primarily poplar/cottonwood ET test cover for a period of one year following the harvest of all woody biomass exceeding a height of 30 cm above ground surface. Results were compared to previously reported drainage observed during the years leading up to the coppice event. In the first year following coppice, the ET cover was found to be 93% effective at redirecting moisture during the spring/summer season, and 95% effective during the subsequent fall/winter season. This was slightly lower than the 95% and 100% efficacy observed in the spring/summer and fall/winter seasons, respectively, during the final measured year prior to coppice. However, the post-coppice efficacy was higher than the efficacy observed during the first three years following establishment of the cover. While additional longer-term studies are recommended, this project demonstrated that woody ET covers could potentially produce harvestable biomass while still effectively managing aerial moisture.     

Water-soluble granules containing <Emphasis Type="Italic">Bacillus megaterium</Emphasis> for biological control of rice sheath blight: formulation,bacterial viability and efficacy testing

Endospores of B. megaterium were formulated in granule formulations with sodium alginate, lactose and polyvinylpyrrolidone (PVP K-30) by the wet granulation technique. The granule formulation exhibited good physical characteristics, such as high-water solubility and optimal viscosity, that would be suitable for spray application. The bacteria remained viable in the dry granule formulation at 10⁹ c.f.u./g after 24 months storage at room temperature. Under laboratory conditions, aqueous solutions of the formulation showed high activity against mycelial growth of R. solani (99.64 ± 0.14% mycelial inhibition). High viability of the bacterial antagonist on leaf sheath and leaf blade at day 7 after spraying with the formulation was observed (approximately 10⁶ c.f.u./g of plant). Application of an equivalent number of un-formulated endospores resulted in much loss of the bacterial endospores even 1 day after application. In a small pilot field study, an aqueous solution of the formulation (3%w/v) applied by spraying at days 1, 5 and 10 after pathogen inoculation of the rice plants was more effective in suppressing rice sheath blight disease than one application of a fungicide (Iprodione) at day 1. Additionally, rice plants sprayed with the aqueous solution of the granule formulation had higher panicle and whole kernel weights than those of fungicide-treated and control (untreated) plants.     

Response of calcareous grassland vegetation to mowing and fluctuating weather conditions

Question: What determines the balance between the cover values of vascular plants, lichens and mosses in dry calcareous grassland communities? Location: Western Estonia. Methods: A five‐year (2001–2005) study was conducted in a dry calcareous grassland. The cover of mosses, lichens and vascular plants and all moss species was recorded in permanent plots. Vascular plants were cut in half of the plots. Data from a nearby weather station were used to calculate mean values of different weather parameters and a summer moisture index for the study years. Results: Significant differences in cover values between years were found. The fluctuations of total moss cover and the cover of the dominating moss species Ctenidium molluscum followed changes in annual precipitation. Both cover values were highest in years with high precipitation. The cover change of vascular plants was best characterized by the moisture index of the growth period (three summer months). Summers with high moisture indexes facilitated vascular plant and lichen growth. Annual precipitation and the cover of mosses had a negative influence on the cover of vascular plants. The cutting of vascular plants did not have a significant effect on moss and lichen cover. Conclusions: 1. On dry calcareous grasslands the growth of mosses is enhanced by high annual precipitation, while the growth of vascular plants and lichens is influenced rather by the high summer moisture index. The cover of vascular plants is inhibited by the large moss cover. 2. Mowing of vascular plants does not influence the cover of mosses and lichens.     

Evaluation of Toxicity of <Emphasis Type="Italic">Cercospora piaropi</Emphasis> in a Mycoherbicide Formulation by Using Bacterial Bioluminescence and the Ames Mutagenicity Tests

An evaluation of the potential hazards associated with mutagenicity and acute toxicity of a mycoherbicide formulation based on the fungal pathogen Cercospora piaropi was performed. Neither the mycoherbicide nor any of its components were mutagenic to Salmonella typhimurium TA98 and TA100 with or without metabolic activation. Both the C. piaropi and the mycoherbicide formulation were shown to be moderately toxic with a bacterial bioluminescence assay. No acute toxicity was found in water samples taken from tanks after treatment of water hyacinth with the mycoherbicide.     

Growth of potato cultivars in response to application of phosphate fertiliser

Three experiments examined the response of potato cultivars from different maturity groups to fertiliser phosphorus application under conditions of relatively low residual soil P. Initial expansion of the leaf canopy was much more rapid following P application and maximum cover was attained sooner. In the absence of applied P, maximum ground cover was reduced substantially in early-maturing cultivars but not in maincrop cultivars. At early harvests, all cultivars showed very large growth responses to P application, but cv. Rocket grown from well-sprouted seed showed a significantly larger response than cv. Desiree. In the absence of applied P, ground cover was in some cases higher at later growth stages allowing a substantial degree of growth compensation so that final harvests showed only small effects of P application on dry matter yields. At final harvests, no significant interactions between cultivar and phosphorus fertiliser level were found for either dry matter production or P uptake despite some apparent effects. Phosphorus application increased dry matter production through increased interception of solar radiation with no effect on efficiency of utilisation.     

Cloud shading and fog drip influence the metabolism of a coastal pine ecosystem

Assessing the ecological importance of clouds has substantial implications for our basic understanding of ecosystems and for predicting how they will respond to a changing climate. This study was conducted in a coastal Bishop pine forest ecosystem that experiences regular cycles of stratus cloud cover and inundation in summer. Our objective was to understand how these clouds impact ecosystem metabolism by contrasting two sites along a gradient of summer stratus cover. The site that was under cloud cover ~15% more of the summer daytime hours had lower air temperatures and evaporation rates, higher soil moisture content, and received more frequent fog drip inputs than the site with less cloud cover. These cloud‐driven differences in environmental conditions translated into large differences in plant and microbial activity. Pine trees at the site with greater cloud cover exhibited less water stress in summer, larger basal area growth, and greater rates of sap velocity. The difference in basal area growth between the two sites was largely due to summer growth. Microbial metabolism was highly responsive to fog drip, illustrated by an observed ~3‐fold increase in microbial biomass C with increasing summer fog drip. In addition, the site with more cloud cover had greater total soil respiration and a larger fractional contribution from heterotrophic sources. We conclude that clouds are important to the ecological functioning of these coastal forests, providing summer shading and cooling that relieve pine and microbial drought stress as well as regular moisture inputs that elevate plant and microbial metabolism. These findings are important for understanding how these and other seasonally dry coastal ecosystems will respond to predicted changes in stratus cover, rainfall, and temperature.     

Brazilian isolates of Clonostachys rosea: colonization under different temperature and moisture conditions and temporal dynamics on strawberry leaves

Aims: In a research programme for managing diseases caused by Botryis cinerea, four isolates of the antagonistic fungus Clonostachys rosea (Cr) were obtained from different ecosystems in Brazil. We studied ecological requirements for the colonization of strawberry leaves by these isolates. Methods and Results: Temperature effects on both mycelial growth in vitro and leaf colonization by Cr were studied. At 10°C, growth on potato dextrose agar and colonization of leaf discs were poor. Optimum temperature for mycelial growth and leaf colonization was around 25°C. The isolates were applied to leaves which were exposed to 0–48 h intervals of moisture. They were also applied to leaves which remained from 0 to 36 h without wetness. All isolates efficiently colonized leaves, regardless of moisture interval or the delay to begin wetness. Although all isolates survived in green leaves of whole plants, colonization decreased throughout a 49‐day period. Conclusions: Brazilian isolates of Cr can establish and colonize strawberry leaves under a wide range of temperature and moisture conditions. Significance and Impact of the Study: It is expected that the Brazilian isolates of Cr will establish efficiently in strawberry leaves where they can compete with B. cinerea.     

Influence of Temperature, Wetness Duration, and Leaf Type on the Quantification of Monocyclic Parameters of Bean Rust

Monocyclic parameters of bean rust (Uromyces phaseoli var. typical) were quantified in growth chambers, on rwo bean cultivars for three temperatures (17, 21, and 25 °C), two types of leaves (unifoliolate and trifoiiolate leaves), and nine leaf wetness periods (0, 4, 7, 10, 13, 16, 19, 22, and 25 hrs). The expression of disease was greatly influenced by past-inoculation temperatures. The incubation and latent periods were shortest at 21 °C for both cultivars and leaf types. For both cultivars, trifoiiolate leaves were more susceptible than unifoliolate leaves. A wetness period of at least four hours was required for disease to occur. The maximum disease efficiency for both cultivars occurred with 22 hrs of leaf wetness at 17 °C. The disease efficiencies for temperatures of 17–29 °C and leaf wetness periods of 0–25 hrs were adequately described by a response-surface model. Because of the great influence of temperature and leaf wetness on infection, bean rust is unlikely to occur at high temperatures (> 25°C) and short leaf wetness periods (< 7 hrs).     

Effects of inoculum concentration, leaf age and wetness period on the development of dark leaf and pod spot (Alternaria brassicae) on oilseed rape (Brassica napus)

Experiments were done under controlled environment and glasshouse conditions to study the effects of inoculum concentration, leaf age and wetness period on the development of dark leaf and pod spot (Alternaria brussicae) on oilseed rape (Brassica napus). On leaves of potted oilseed rape plants (cv. Bienvenu) inoculated with A. brassicae conidial suspensions, the severity (number of lesions cm^-2) of dark leaf spot increased as inoculum concentration increased from 80 to 660 spores ml^-1and as leaf age increased from 4 to 14 days. On pods on detached racemes of spring oilseed rape (cv. Starlight), the incidence of dark pod spot (% of pods diseased) increased as inoculum concentration increased from 80 to 10⁴spores ml^-1. Increasing inoculum concentration above 10⁴spores ml^-1did not increase the incidence but did increase the severity of dark pod spot. A minimum wetness period of 4 h was needed for infection of oilseed rape leaves (cv. Envol) by A. brussicue at 18°C and disease severity increased with increasing wetness period up to 12 h. The length of dry interruptions after 3–8 h of initial wetness affected the severity of dark leaf spot. A second wetness period increased the severity of dark leaf spot if the dry interruption was ≤ 6 h and if the first wetness period was ≤ 8 h. The incubation period of A. brassicae decreased from 3.5 to 2.5 days as inoculum concentration increased from 80 to 660 spores ml^-on leaves (cv. Bienvenu) at 17–25°C and from 3.8 to 1.0 day as inoculum concentration increased from 80 to ≥2 ≥ 10³spores ml^-1on pods (cv. Starlight) at 18°C.     

Epidemiology of Cladosporium allii and Cladosporium allii-cepae, leaf blotch pathogens of leek and onion.

Conidia of Cladosporium allii and C. allii-cepae germinated over the temperature range 2–30°C on agar with optimal responses at 15–20°C (C. allii) and 20°C (C. allii-cepae). Conidia of both fungi germinated in water and at c. 100% relative humidity (r.h.) but not at lower humidities on leaf and glass slide surfaces. Germination was more rapid when spores were applied dry to agar or leaves than when applied in water or nutrient solution. More lesions developed when conidia of C. allii-cepae were deposited dry on onion leaf discs or leaf surfaces than when they were applied suspended in water. Conidia of both fungi required 18–20 h at c. 100% r.h. to germinate and infect when applied dry to leaves. Damaging the leaves or the addition of nutrients to the leaf surface increased the incidence of infection by C. allii-cepae compared to controls. Inoculated onion bait plants placed out-of-doors developed infection after at least 17 h at c. 100% r.h. or with leaf wetness. Similar conditions were necessary for infection of bait plants exposed in onion and leek crops infected by C. allii-cepae and C. allii respectively. Disease development and spread of infection occurred at different rates over the same period in two different cultivars of leeks, with spore concentrations increasing in proportion to disease. Spore numbers in the air fell considerably when infected leeks were ploughed under.     

Seasonal ultrasonic acoustic emissions of <Emphasis Type="Italic">Quercus ilex</Emphasis> L. trees in a Mediterranean forest

Ultrasonic acoustic emissions were measured in Quercus ilex trees of a Mediterranean forest in Catalonia (NE Spain) each season from summer of 2004 to autumn of 2005. Acoustic emissions were maximum during hot and dry summer periods. Acoustic emissions started below 17% soil moisture, 0.85 RWC, and 2.5 MPa leaf water potential. They were negatively correlated with soil moisture and leaf water potential. The relationship between acoustic emissions and leaf water potential was the strongest, indicating that xylem tension is the most important factor inducing both cavitation (acoustic emissions) and a decrease in leaf water potential. Future increase of xylem cavitation derived from climate change may result in growth and survival limitations for this species in the drier southern limits of its current distribution.     

Pathogenicity of Sclerotinia sclerotiorum on Ranunculus acris in Dairy Pasture

Fifty-four isolates of Sclerotinia sclerotiorum from Ranunculus acris and other natural hosts were applied as mycelial infested kibbled wheat onto 6 month-old R. acris plants in two glasshouse screening experiments. Most isolates (90%) did not differ in their pathogenicity towards R. acris. One isolate, S. sclerotiorum G45, was selected based on its ability to cause severe disease and suppress regeneration of R. acris. A field experiment was conducted to determine the efficacy of S. sclerotiorum (G45) against R. acris in infested dairy pastures in the Takaka Valley, Golden Bay, New Zealand. Isolate G45 was formulated as a wettable powder and was applied as a slurry at 20 and 40 ml/plant in December 1995. After 10 weeks, regeneration from the crown of treated plants was apparent and a second application of S. sclerotiorum was made in February 1996. Best control of R. acris was obtained when the plants were inoculated in full flower in December. At the first time of treatment, the 40 ml application of S. sclerotiorum slurry reduced the total dry weight of R. acris by an average of 57%. The second application had no effect on total dry weight, possibly because moisture levels were not sufficient for S. sclerotiorum infection. This study confirmed S. sclerotiorum to be an aggressive pathogen of R. acris under both glasshouse and field conditions. As a result, this pathogen has potential as a mycoherbicide for R. acris. Further experiments are required to explore ways of enhancing the efficacy of S. sclerotiorum against R. acris by manipulation of the host, pathogen and environment.     

Temperature and Leaf Wetness Effects on Infection of Sugarcane by Puccinia melanocephala

Brown rust epidemics in sugarcane, caused by Puccinia melanocephala, vary in severity between seasons. To improve the understanding of disease epidemiology, the effects of leaf wetness, temperature and their interaction on infection of sugarcane by the pathogen were studied under controlled conditions. Disease severity was low at 15 and 31°C regardless of leaf wetness duration. No infection occurred with a 4‐h leaf wetness period. Increasing leaf wetness duration from 7 to 13 h lowered the temperature required for disease onset from 21 to 17°C. More infection occurred with 13 compared to 10 h of leaf wetness at 17°C, and severity decreased for all leaf wetness periods at 29 compared to 27°C. Postinfection suboptimal low and high temperatures increased the time required for lesion development and high temperatures decreased maximum disease severity. The observed effects of leaf wetness and temperature on infection by P. melanocephala could help explain the initiation, rate of increase and decline of brown rust epidemics in the field.     

On the effect of soil wetness on thermal stress

A coupled atmosphere-soil model was applied in order to evaluate the impact of soil wetness on human stress in the absence of horizontal gradients in moisture. The results are illustrated and discussed with consideration to various combinations of wind speed and lower level atmospheric moisture during daylight hours with summer weather conditions. A thermal index composed of the air temperature and wet-bulb temperature does not show major changes as a function of variation of soil mosture. When wind speed and solar radiation are also considered, in a more detailed thermal index, relatively wet soil is associated with the optimal thermal comfort.     

Biology and Ecology of Altica carduorum Chrysomelidae: Coleoptera from North-western China: A Potential Biocontrol Agent for Cirsium arvense Asteraceae in Canada

The biotype of the defoliating beetle, Altica carduroum, from Wusu Xinjiang, China was studied as a biocontrol agent for Cirsium arvense in Canada. At Wusu, the beetle is particularly damaging to C. arvense in irrigated crops and fallow fields. A release of 300 adult A. carduorum at Urumqi, Xinjiang, dispersed to cover an area with a radius of 600 m by the following year, where it destroyed almost 60 of C. arvense leaves and resulted in plant wilting at a density of 4.5 beetles plant. Laboratory studies of the beetle' s development of 2 C intervals from 15 to 27 C identified the optimum developmental temperature as 25.5 C. Beetles reared at this temperature laid an average of 245 eggs, with a 41-fold generation increase. Habitat comparisons between biotypes of A. carduorum from Wusu and Europe suggest that the Wusu biotype may be better suited as a biocontrol agent of C. arvense on the Canadian prairies.     

Effects of Temperature and Moisture Variables on Brown Rust Epidemics in Sugarcane

Epidemics of brown rust in sugarcane, caused by Puccinia melanocephala, vary in severity between seasons. Natural epidemics were studied to determine the effects of temperature and moisture variables on epidemic onset, severity and decline. Variables were monitored with disease severity in two cultivars, each grown at a different location in Louisiana. Maximum daily temperature was the variable most correlated with seasonal epidemic development and decline. Disease severity was high during 2009 and low during 2010. This contrast allowed evaluation of the effects of conducive and limiting environmental conditions on severity. Lower severity resulted from a combination of unfavourable temperature and leaf wetness conditions that delayed onset then reduced the rate of disease increase. An accumulation of 23–25 days with leaf wetness periods of at least 7 h after the daily minimum temperature exceeded 17°C preceded the onset of disease on young leaves in both severe and mild epidemics. Severe epidemics in both cultivars declined once maximum ambient daily temperature was 32°C or higher. Low and high limiting temperatures determined the initiation and decline of an epidemic, respectively, under Louisiana climatic conditions. The availability of leaf wetness was then an important determinant of disease severity during the epidemic.     

Air humidity as key determinant of morphogenesis and productivity of the rare temperate woodland fern Polystichum braunii

(1) Most ferns are restricted to moist and shady habitats, but it is not known whether soil moisture or atmospheric water status are decisive limiting factors, or if both are equally important. (2) Using the rare temperate woodland fern Polystichum braunii, we conducted a three‐factorial climate chamber experiment (soil moisture (SM) × air humidity (RH) × air temperature (T)) to test the hypotheses that: (i) atmospheric water status (RH) exerts a similarly large influence on the fern's biology as soil moisture, and (ii) both a reduction in RH and an increase in air temperature reduce vigour and growth. (3) Nine of 11 morphological, physiological and growth‐related traits were significantly influenced by an increase in RH from 65% to 95%, leading to higher leaf conductance, increased above‐ and belowground productivity, higher fertility, more epidermal trichomes and fewer leaf deformities under high air humidity. In contrast, soil moisture variation (from 66% to 70% in the moist to ca. 42% in the dry treatment) influenced only one trait (specific leaf area), and temperature variation (15 °C versus 19 °C during daytime) only three traits (leaf conductance, root/shoot ratio, specific leaf area); RH was the only factor affecting productivity. (4) This study is the first experimental proof for a soil moisture‐independent air humidity effect on the growth of terrestrial woodland ferns. P. braunii appears to be an air humidity hygrophyte that, whithin the range of realistic environmental conditions set in this study, suffers more from a reduction in RH than in soil moisture. A climate warming‐related increase in summer temperatures, however, seems not to directly threaten this endangered species.     

Vertical patterns and duration of surface wetness in an old-growth tropical montane forest, Indonesia

In tropical montane forests, the wetness of leaf surfaces is an important parameter which may influence gas exchange, growth and vitality of leaves, and forest productivity. Thirty surface wetness sensors were operated during May–August 2004 in a vertical profile inside an old-growth lower montane rain forest of Central Sulawesi, Indonesia, with the objective to analyse spatial and temporal patterns of surface wetness and to relate wetness duration to the microclimate inside the stand. The canopy was wet during 25–30% of time in this study period. In a dry period, however, surface wetness lasted for only 5% of the time, whereas the canopy was wet during 45–55% of the time in a rainy period. In the lower shade canopy, surface wetness continuously existed for periods of up to 22 h and more, although rainfall occurred only during afternoon thunderstorms of limited duration. The long duration of surface wetness has implications for forest interception models, which assume a complete drying of the canopy between subsequent rainfall events. In periods with rainfall, leaf wetness typically occurred in the afternoon, evening and first half of the night because intercepted water persisted on the leaves until about midnight. In dry periods, in contrast, surface wetness was mainly caused by dewfall in the second half of the night, and it occurred mainly in the uppermost canopy where radiative heat losses resulted in a substantial under-cooling of the leaves. Ecophysiological and hydrological importance is suggested by the long duration of surface wetting in this stand with possible implications for gas exchange, leaf growth, leaf colonization by epiphylls and the forest water balance.