Temperature-growth Responses Research Articles

“Salicylic acid enhances thermotolerance and antioxidant defense in Trigonella foenum graecum L. under heat stress”

Plants possess various defense mechanisms to cope with genotoxic and environmental challenges, with high temperatures posing a significant threat due to global warming. In this investigation, ten-day-old Trigonella foenum-graecum (fenugreek) seedlings were cultivated in a controlled environment chamber with conditions set at 70–80% relative humidity, a day/night cycle of 25/18 °C, and a photosynthetically active radiation (PAR) of 1000 μmol m−2 s−1. Other groups of seedlings were subjected to temperatures of 30, 35, or 40 °C. Our research aimed to investigate the relationship between temperature intensity, duration, growth responses, physiological and metabolic activities, and the stress alleviation by salicylic acid. The results demonstrated that high temperatures significantly reduced plant growth, membrane stability, while increasing proline and protein content, as well as electrolyte leakage in the leaves. The most pronounced results were observed when exposed to 40 °C for 24 h. Salicylic acid completely mitigated the negative impacts of high-temperature stress when it was applied at 40 °C for 24 h. We utilized two-dimensional electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to examine proteins across three groups: control plants, stressed plants, and plants subjected to salicylic acid treatment. Our results revealed that, among the proteins influenced by high-temperature stress, 12 displayed the most significant differences in regulation. These stress-responsive proteins played roles in signal transduction, stress defense, detoxification, amino acid metabolism, protein metabolism (including translation, processing, and degradation), photosynthesis, carbohydrate metabolism, and energy pathways. These proteins may hold practical implications for diverse biological activities. In conclusion, salicylic acid treatment enhanced thermotolerance in fenugreek plants, although further investigation is required at the genome level to elucidate the mechanism of salicylic acid action under heat stress.

Investigating quorum-quenching marine bacilli as potential biocontrol agents for protection of shrimps against Early Mortality Syndrome (EMS)

Early Mortality Syndrome (EMS) has been a major problem for shrimp aquaculture in Southeast Asia due to its epizootic prevalence within the region since the first reported case in 2009. This study explores the application of halophilic marine bacilli isolated from coral mucus and their quorum-quenching abilities as potential biocontrol agents in aquaculture systems to combat the causative agent of EMS, Vibrio parahaemolyticus. N-acylhomoserine lactone (AHL)-degrading (AiiA) activity was first screened by PCR then confirmed by bio-reporter assay, and a combination of 16S rDNA sequence analysis and quantitative phenotype assays including biofilm-formation and temperature-growth responses were used to demonstrate diversity amongst these quorum-quenching isolates. Three phenotypically distinct strains showing notable potential were chosen to undergo co-cultivation as a method for strain improvement via long term exposure to the pathogenic V. parahaemolyticus. The novel approach taken led to significant improvements in antagonism and quorum quenching activities as compared to the ancestral wild-type strains and offers a potential solution as well as pathway to improve existing beneficial microbes for one of the most pressing issues in shrimp aquacultures worldwide.

Phytophthora palmivora Causing Disease on Theobroma cacao in Hawaii

Commercial production of cacao in Hawaii has doubled in the past 10 years, and farmers are receiving premium prices for their beans from the expanding local confectionery industry. Black pod, caused by Phytophthora spp., is the only major cacao disease that has been reported in Hawaii but distribution and molecular identification are lacking. To determine the species of Phytophthora affecting Theobroma cacao, a sampling trip was conducted on Hawaii Island and Oahu. Ten isolates of Phytophthora palmivora were obtained from diseased cacao on Hawaii Island, but none from Oahu, despite the presence of symptomatic pods. No other Phytophthora species were found. Laboratory studies showed that all isolates produced lesions on unwounded cacao pods, but they differed in terms of their temperature–growth responses. Fungicide sensitives for a subset of isolates (n = 4) were determined using media amended with a range of fungicide concentrations. The Hawaiian isolates of P. palmivora were more sensitive to mefenoxam, chlorothalonil, and fosetyl-Al, than isolates from Ghana (n = 2) and Mexico (n = 1). This study identifies P. palmivora as a causal agent of black pod in Hawaii based on molecular data and provides valuable preliminary information on fungicide resistance and temperature response that can be used to improve disease management.

Higher Winter-Spring Temperature and Winter-Spring/Summer Moisture Availability Increase Scots Pine Growth on Coastal Dune Microsites Around the South Baltic Sea

Coastal sand dunes near the Baltic Sea are a dynamic environment marking the boundary between land and sea and oftentimes covered by Scots pine (Pinus sylvestris L.) forests. Complex climate-environmental interactions characterize these ecosystems and largely determine the productivity and state of these coastal forests. In the face of future climate change, understanding interactions between coastal tree growth and climate variability is important to promote sustainable coastal forests. In this study, we assessed the effect of microsite conditions on tree growth and the temporal and spatial variability of the relationship between climate and Scots pine growth at nine coastal sand dune sites located around the south Baltic Sea. At each site, we studied the growth of Scots pine growing at microsites located at the ridge and bottom of a dune and built a network of 18 ring width and 18 latewood blue intensity tree-ring chronologies. Across this network, we found that microsite has a minor influence on ring width variability, basal area increment, latewood blue intensity, and climate sensitivity. However, at the local scale, microsite effects turned out to be important for growth and climate sensitivity in some sites. Correlation analysis indicated that. the strength and direction of climate-growth responses for the ring width and blue intensity chronologies were similar for climate variables over the 1903-2016 period. A strong and positive relationship between ring width and latewood blue intensity chronologies with winter-spring temperature was detected at local and regional scales. We identified a relatively strong, positive influence of winter-spring/summer moisture availability on both tree-ring proxies. When climate-growth responses between two intervals (1903-1959, 1960-2016) were compared, the strength of growth responses to temperature and moisture availability for both proxies varied. More specifically for the ring-width network, we identified decreasing temperature-growth responses, which is in contrast to the latewood blue intensity network, where we documented decreasing and increasing temperature-growth relationships in the north and south respectively. We conclude coastal Scots pine forests are primarily limited by winter or winter-spring temperatures and drought despite differing microsite conditions. We detected some spatial and temporal variability in climate-growth relationships that warrant further investigation.

Meta‐analysis reveals enhanced growth of marine harmful algae from temperate regions with warming and elevated CO2 levels

Elevated pCO2 and warming may promote algal growth and toxin production, and thereby possibly support the proliferation and toxicity of harmful algal blooms (HABs). Here, we tested whether empirical data support this hypothesis using a meta‐analytic approach and investigated the responses of growth rate and toxin content or toxicity of numerous marine and estuarine HAB species to elevated pCO2 and warming. Most of the available data on HAB responses towards the two tested climate change variables concern dinoflagellates, as many members of this phytoplankton group are known to cause HAB outbreaks. Toxin content and toxicity did not reveal a consistent response towards both tested climate change variables, while growth rate increased consistently with elevated pCO2. Warming also led to higher growth rates, but only for species isolated at higher latitudes. The observed gradient in temperature growth responses shows the potential for enhanced development of HABs at higher latitudes. Increases in growth rates with more CO2 may present an additional competitive advantage for HAB species, particularly as CO2 was not shown to enhance growth rate of other non‐HAB phytoplankton species. However, this may also be related to the difference in representation of dinoflagellate and diatom species in the respective HAB and non‐HAB phytoplankton groups. Since the proliferation of HAB species may strongly depend on their growth rates, our results warn for a greater potential of dinoflagellate HAB development in future coastal waters, particularly in temperate regions.

Tree-ring isotopes suggest atmospheric drying limits temperature-growth responses of treeline bristlecone pine.

Altitudinally separated bristlecone pine populations in the White Mountains (California, USA) exhibit differential climate–growth responses as temperature and tree-water relations change with altitude. These populations provide a natural experiment to explore the ecophysiological adaptations of this unique tree species to the twentieth century climate variability. We developed absolutely dated annual ring-width chronologies, and cellulose stable carbon and oxygen isotope chronologies from bristlecone pine growing at the treeline (~3500 m) and ~200 m below for the period AD 1710–2010. These chronologies were interpreted in terms of ecophysiological adaptations to climate variability with a dual-isotope model and a leaf gas exchange model. Ring widths show positive tree growth anomalies at treeline and consistent slower growth below treeline in relation to the twentieth century warming and associated atmospheric drying until the 1980s. Growth rates of both populations declined during and after the 1980s when growing-season temperature and atmospheric vapour pressure deficit continued to increase. Our model-based interpretations of the cellulose stable isotopes indicate that positive treeline growth anomalies prior to the 1980s were related to increased stomatal conductance and leaf-level transpiration and photosynthesis. Reduced growth since the 1980s occurred with a shift to more conservative leaf gas exchange in both the treeline and below-treeline populations, whereas leaf-level photosynthesis continued to increase in response to rising atmospheric CO2 concentrations. Our results suggest that warming-induced atmospheric drying confounds positive growth responses of apparent temperature-limited bristlecone pine populations at treeline. In addition, the observed ecophysiological responses of attitudinally separated bristlecone pine populations illustrate the sensitivity of conifers to climate change.

Temperature oscillation coupled with fungal community shifts can modulate warming effects on litter decomposition

Diel temperature oscillations are a nearly ubiquitous phenomenon, with amplitudes predicted to change along with mean temperatures under global-warming scenarios. Impact assessments of global warming have largely disregarded diel temperature oscillations, even though key processes in ecosystems, such as decomposition, may be affected. We tested the effect of a 5 degrees C temperature increase with and without diel oscillations on litter decomposition by fungal communities in stream microcosms. Five temperature regimes with identical thermal sums (degree days) were applied: constant 3 degrees and 8 degrees C; diel temperature oscillations of 5 degrees C around each mean; and oscillations of 9 degrees C around 8 degrees C. Temperature oscillations around 8 degrees C (warming scenario), but not 3 degrees C (ambient scenario), accelerated decomposition by 18% (5 degrees C oscillations) and 31% (9 degrees C oscillations), respectively, compared to the constant temperature regime at 8 degrees C. Community structure was not affected by oscillating temperatures, although the rise in mean temperature from 3 degrees to 8 degrees C consistently shifted the relative abundance of species. A simple model using temperature-growth responses of the dominant fungal decomposers accurately described the experimentally observed pattern, indicating that the effect of temperature oscillations on decomposition in our warming scenario was caused by strong curvilinear responses of species to warming at low temperature, particularly of the species becoming most abundant at 8 degrees C (Tetracladium marchalianum). These findings underscore the need to consider species-specific temperature characteristics in concert with changes in communities when assessing consequences of global warming on ecosystem processes.

Effect of temperature on vegetative growth of Beauveria bassiana isolates from different origins

Effects of temperature on growth on a semisynthetic medium of 65 isolates of Beauveria bassiana from different geoclimatic and host origins were determined. The isolates were grouped according to the climate of their geographic origin, distinguishing between cool and warm regions; according to their host origin, distinguishing between isolates from acridids or from soil associated with acridid populations; and according to host order. In general, B. bassiana grew at a wide temperature range from 8 to 35 C. A well defined maximum thermal threshold occurred at temperatures of >35–37 C for 50 isolates; >32–35 C for 12; and >30–32 C for 1 isolate. The lower temperature threshold for all isolates tested was below 8 C. Relative growth rate, calculated from the maximum growth rate for each isolate, was significantly affected by temperature and isolate. Optimal temperatures were generally between 25 and 28 C with several isolates exhibiting optimal growth at temperatures as low as 20 or as high as 30 C. Relative growth rates were not very useful in distinguishing differences among many of the isolates at the near-optimal temperatures. In contrast, the ability to distinguish differences in relative growth rates among isolates increased progressively as temperatures increased above 28 C or decreased below 20 C. There were no apparent relationships between relative growth rates and climatic origin. In comparisons of acridid-associated isolates, relative growth rates were higher for the insect isolates at 8 C and for the African soil isolates at 35 C. At the other temperatures, no clear relationships were apparent. When comparisons were made according to host order, there were significant differences in relative growth rates according to host order at 8, 11, 30, and 32 C but not at the other temperatures. Since temperature growth responses varied considerably among isolates, with some having wide ranges of temperature optima while others were much more restricted, strain selection according to thermal requirements may be warranted when choosing a strain for development as a microbial control agent.

Effect of Temperature on Vegetative Growth of Beauveria bassiana Isolates from Different Origins

Effects of temperature on growth on a semisynthetic medium of 65 isolates of Beauveria bassiana from different geoclimatic and host origins were determined. The isolates were grouped according to the climate of their geographic origin, distinguishing between cool and warm regions; according to their host origin, distinguishing between isolates from acridids or from soil associated with acridid populations; and according to host order. In general, B. bassiana grew at a wide temperature range from 8 to 35 C. A well defined maximum thermal threshold occurred at temperatures of >35–37 C for 50 isolates; >32–35 C for 12; and >30–32 C for 1 isolate. The lower temperature threshold for all isolates tested was below 8 C. Relative growth rate, calculated from the maximum growth rate for each isolate, was significantly affected by temperature and isolate. Optimal temperatures were generally between 25 and 28 C with several isolates exhibiting optimal growth at temperatures as low as 20 or as high as 30 C. Relative growth rates were not very useful in distinguishing differences among many of the isolates at the near-optimal temperatures. In contrast, the ability to distinguish differences in relative growth rates among isolates increased progressively as temperatures increased above 28 C or decreased below 20 C. There were no apparent relationships between relative growth rates and climatic origin. In comparisons of acridid-associated isolates, relative growth rates were higher for the insect isolates at 8 C and for the African soil isolates at 35 C. At the other temperatures, no clear relationships were apparent. When comparisons were made according to host order, there were significant differences in relative growth rates according to host order at 8, 11, 30, and 32 C but not at the other temperatures. Since temperature growth responses varied considerably among isolates, with some having wide ranges of temperature optima while others were much more restricted, strain selection according to thermal requirements may be warranted when choosing a strain for development as a microbial control agent.

Effect of temperature on vegetative growth among isolates of Metarhizium anisopliae and M. flavoviride.

Effects of temperature on vegetative growth on a semi-synthetic medium of 22 isolates of Metarhizium anisopliae and 14 isolates of M. flavoviride were determined. The majority of isolates of both species grew between 11 and 32 degrees C; several isolates grew at 8 and 37 degrees C. None of the isolates grew at 40 degrees C. Relative growth rate, calculated from the maximum growth rate for each isolate, was significantly affected by temperature and isolate, with significant isolate * temperature interactions. The maximum absolute growth rates among the isolates ranged from 2.5 mm to 5.9 mm/day. Optimal temperatures were generally between 25 and 32 degrees C with several isolates exhibiting optimal growth at temperatures as high as 32 degrees C. Overall, relative growth rates were greater in isolates of M. anisopliae than M. flavoviride at temperatures of 25 degrees C or lower; conversely mean relative growth rates were greater in M. flavoviride than M. anisopliae at temperatures higher than 25 degrees C. However, the two most cold tolerant isolates at 8 degrees C were M. flavoviride and the three most heat tolerant at 35 degrees C were M. anisopliae. Since temperature growth responses varied considerably between isolates, strain selection according to thermal tolerance may be warranted when choosing a strain for development as a microbial control agent.

Athelia arachnoidea, the sexual state ofRhizoctonia carotae, a pathogen of carrot in cold storage

Athelia arachnoidea was collected during winter on dead leaves of deciduous trees in Oregon. Minute sclerotia (0.2-1.0 mm) were seen on hyme- nia, whereas in culture sclerotia were much larger (1.0-5.0 mm). The pathogenicity, morphological characteristics, and temperature growth responses of the anamorphic state, were identical to Rhizoctonia carotae. The relationship between the sclerotial ana? morph and the teleomorph was confirmed by DNA sequence of the internal transcribed spacers of the nuclear ribosomal repeat unit. The sequences were homologous among the specimens of A. arachnoidea and the sclerotial anamorph from Oregon, A. arach? noidea and R. carotae isolates from culture collec? tions, and several isolates of R. carotae from carrot cold-storage facilities. Like R. carotae, A. arachnoidea produced abundant crystals of calcium oxalate on the hyphae, was pathogenic on carrot at 3 C, and caused crater rot symptoms equivalent in severity. Sclerotia of A. arachnoidea-R. carotae did not germi? nate under conditions suitable for eruptive germi? nation in A. rolfsii. The DNA sequence of A. epiphylla from Europe was identical (within 6 bp) to A. arach? noidea-R. carotae, whereas A. epiphylla from North America varied by 34-46 independent base pair changes. Athelia epiphylla and A. arachnoidea formed similar sclerotia. Connecting the Rhizoctonia root pathogen to the Athelia teleomorph links the dispa- rate literatures on the natural history of this fungus and reveals significant insights into the epidemiology of the disease. Fibularhizoctonia gen. nov. is proposed to encompass Rhizoctonia species with clamp connec? tions, and the description of R. carotae and R. centri- fuga are emended.

Athelia arachnoidea, the Sexual State of Rhizoctonia carotae, a Pathogen of Carrot in Cold Storage

Athelia arachnoidea was collected during winter on dead leaves of deciduous trees in Oregon. Minute sclerotia (0.2–1.0 mm) were seen on hymenia, whereas in culture sclerotia were much larger (1.0–5.0 mm). The pathogenicity, morphological characteristics, and temperature growth responses of the anamorphic state, were identical to Rhizoctonia carotae. The relationship between the sclerotial anamorph and the teleomorph was confirmed by DNA sequence of the internal transcribed spacers of the nuclear ribosomal repeat unit. The sequences were homologous among the specimens of A. arachnoidea and the sclerotial anamorph from Oregon, A. arachnoidea and R. carotae isolates from culture collections, and several isolates of R. carotae from carrot cold-storage facilities. Like R. carotae, A. arachnoidea produced abundant crystals of calcium oxalate on the hyphae, was pathogenic on carrot at 3 C, and caused crater rot symptoms equivalent in severity. Sclerotia of A. arachnoidea-R. carotae did not germinate under conditions suitable for eruptive germination in A. rolfsii. The DNA sequence of A. epiphylla from Europe was identical (within 6 bp) to A. arachnoidea-R. carotae, whereas A. epiphylla from North America varied by 34–46 independent base pair changes. Athelia epiphylla and A. arachnoidea formed similar sclerotia. Connecting the Rhizoctonia root pathogen to the Athelia teleomorph links the disparate literatures on the natural history of this fungus and reveals significant insights into the epidemiology of the disease. Fibularhizoctonia gen. nov. is proposed to encompass Rhizoctonia species with clamp connections, and the description of R. carotae and R. centrifuga are emended.

Phialophora asterisf. sp.helianthi,a New Pathogen of Sunflower in Italy

A wilt disease was observed during the summer of 1993 in a sunflower field near Perugia in central Italy. The disease was characterized by yellowing of leaves as plants approached Dowering. Large areas of the leaves turned light green, usually beginning at the apex and margins and extending inward. Subsequently, leaf margins turned necrotic, and diseased plants were stunted with smaller heads. Our trials proved that this disease was caused by Phialophora asteris f. sp. helianthi. The fungus was examined for colony morphology, temperature growth responses, and pathogenicity. Significant differences were observed among various culture media. Best growth and profuse sporulation were obtained on carrot and Czapeck agars added with peptone. The optimum temperature for growth was 2S C; temperatures of S, 10, IS, and PO C greatly reduced colony growth and sporulation. No growth was observed at PS C. Significant differences in susceptibility to P a. helianthi were observed in 17 sunflower cultivars tested in greenhouse trials; sunflower lines HA 335, 803-1 (=DM-S), HA 89, HA-RI, and RHA 274 were the most resistant. This is the first report of the disease in Italy and Europe

Evidence for distinct isozyme subgroups within Phytophthora citricola and close relationships with P. capsici and P. citrophthora

Fourteen isozyme loci resolved ten electrophoretic types (ETs) amongst a worldwide collection of 125 isolates of P. citricola . The ETs clustered into five distinct subgroups, CIT1–5. CIT1 contained all the isolates from Citrus spp. including the Sawada type culture, the now defunct species P. pini and an authentic isolate of P. cactorum var. applanata . Isolates in subgroups CIT1, CIT2, and CIT3, which differed from each other at only a few enzyme loci, were from diverse locations and hosts. Subgroups CIT4 and CIT5 differed from one another at eight loci and from the other three subgroups by four and five loci, respectively. CIT4 was composed of isolates from native South African plants, and CIT5 of isolates from avocado only. Two isolates from Psidium guajava , previously identified as P. citricola (Ko, 1983), were only distantly related to CIT1–5. Three enzymes (phosphoglucose isomerase, malate dehydrogenase and menadione nitrate reductase) could be used to define subgroups. Examination of temperature growth responses as well as sporangial and oogonial morphology revealed no difference among isolates from subgroups CIT1, CIT2 and CIT3. In contrast, isolates of the avocado subgroup, CIT5, did not survive at temperatures at or above 30 °C, whilst isolates of subgroups CIT1–3 survived temperatures up to 33°. In addition, isolates of CIT5 produced smaller oogonia than those from CIT1–3, although there was some overlap. A comparison of the P. citricola subgroups with P. cactorum revealed a high dissimilarity based on isozyme analysis. However, a close relationship was established between P. citricola, P. capsici and P. citrophthora from both isozyme analysis and mitochondrial DNA restriction patterns. The host-specific group CIT5 clustered with P. capsici and P. citrophthora rather than with other P. citricola subgroups, and may be sufficiently genetically distinct from other subgroups of P. citricola to be regarded as a separate biological taxon.

Temperature-growth responses distinguish the OPC and OPH sibling species within ‘ Ophiostoma piceae’

The temperature-growth relationships of a range of isolates representing the recently identified OPC and OPH sibling species within Ophiostoma piceae were studied. Most OPC isolates grew significantly faster than OPH isolates on 2% Oxoid malt extract agar (MEA) between 17·5 and 27·5 °C, but between 27·5° and 30° growth rates of all OPC isolates studied declined rapidly in contrast to those of OPH isolates. The upper limit for growth of OPC isolates of MEA was ca 35°, whereas that for OPH isolates was ca 31°. A simple growth test at 32° on MEa will discriminate between most isolates of the two species, and can be used as a supplementary aid to their identification.

Temperature requirements for growth and survival of macroalgae from Disko Island (Greenland)

The temperature requirements for growth and upper temperature tolerance were determined in 16 macroalgal species collected on Disko Island (Greenland). The upper survival temperatures were examined in 1°C steps, and growth measured at 5°C intervals between 0 and 20°C using a refined method, where the fresh weight was determined weekly or fortnightly over a period of 5 or 6 weeks. To express temperature-growth responses, growth rates of temperature-acclimated plants were taken. Two groups with different temperature requirements were identified: (1) A stenothermal group includingAcrosiphonia arcta, Acrosiphonia sonderi, Urospora penicilliformis, Devaleraea ramentacea, Desmarestia aculeata, Pilayella littoralis, growing between 0 and (10 to) 15 (or 20)°C with optima between 0 and 10°C. The upper survival temperatures in these species and inChromastrum secundatum, Chromastrum virgatulum, Chordaria flagelliformis were between 17 and 23°C (duration of experiment: 2 weeks). (2) A eurythermal group includingEnteromorpha clathrata, Enteromorpha intestinalis andPolysiphonia urceolata growing between 0 and 20°C with growth optima at 10 or 15°C. The upper survival temperatures in these species and inChaetomorpha tortuosa, Bangia atropurpurea andEudesme virescens were between 24 and 31°C. These algal species showed little adaptation to the Arctic temperatures. In contrast, algae from the first group exhibited a relatively high adaptation to low temperatures — approaching the low temperature requirements of Antarctic algae. The results are discussed in relation to the geographic distribution of individual species.

Taxonomic classification of asexual isolates of Pythium ultimum based on cultural characteristics and mitochondrial DNA restriction patterns

Taxonomic characteristics of 8 isolates of Pythium ultimum and 11 isolates of Pythium in the spherical hyphal swelling (HS) group of Van der Platts-Niterink were compared. Isolates in the two groups had identical temperature growth responses and morphological features of hyphal swellings. All isolates were pathogenic on sugar beet. Attempts to cross HS isolates among themselves and with opposite mating types of P. heterothallicum and P. sylvaticum failed. HS isolates were not induced to form antheridia when paired with isolates of P. ultimum using a polycarbonate membrane sandwich technique. In single culture, some HS isolates formed low numbers of spherical structures encompassed by swollen hyphal masses resembling antheridia. Comparisons of restriction banding patterns of HindIII-digested mitochondrial DNA revealed that all but 1 isolate of P. ultimum were identical; however, the variable isolate shared 80% of the bands in common with the others. Seven of 11 HS isolates had banding patterns identical to the predominant P. ultimum pattern and 1 isolate shared 96% comigrating bands. On the basis of the number of shared characteristics, these isolates appear to be P. ultimum which have lost the ability to reproduce sexually.

Effect of temperature on seasonal occurrence of aquatic hyphomycetes

Seasonal and successional changes in species composition of aquatic hyphomycetes colonizing leaf litter are reported from a small stream in southwestern Michigan, U.S.A. The successional pattern on leaves during the summer was dominated by species typical of tropical and subtropical streams and differed from a cold-season successional pattern at the same site. The spring transition from cold-season to summer species occurred as the maximum temperature approached 20°. In the autumn, cold-season species again assumed dominance as the minimum temperature decreased to 5 °C. The summer successional pattern compared at three sites with different temperatures indicated that cold-season fungal species were dominant at the two cooler, upstream sites. The summer assemblage dominated at the downstream site, and was not detected at either upstream site. Temperature growth responses in culture only partially explain seasonal occurrence, suggesting that interactions among aquatic hyphomycetes play a role in regulating seasonal occurrence.

Simulation of Potato Crop Growth and Development1

Potato (Solanum tuberosum L.) crop yield is the result of net crop dry matter assimilation (NDMA) and fraction of NDMA partitioned to tubers (α) integrated from the day of tuber initiation onset (TIO) through the day of tuber growth cessation (M). These four physiological yield parameters respond to environment and crop development by complex and poorly understood relationships. A crop growth and development model was constructed to determine the integrated temperature sensitivity of the four yield parameters and to test the hypothesis that temperature effects on α may be explained by growth temperature responses of different potato crop components. The crop was divided into three components, canopy, roots, and tubers. Model inputs were daily mean air temperature, soil temperature at 10 cm, solar radiation, and initialization parameters. Simulation began at emergence and continued through three developmental phases, canopy growth, tuber initiation, and tuber growth, which were demarked by four events, emergence, TIO, tuber initiation end, and M. Simulated TIO wau a function of temperature, whereas tuber initiation end and M were indirectly related to both temperature and radiation. Net crop dry matter assimilation was a direct function of incident solar radiation, canopy light interception, and tuber growth rate. Temperature affected NDMA indirectly through effects on canopy light interception and tuber growth rate. Assimilate partitioning was modeled as a function of available assimilates and empirically derived functions of the relationship between potential growth and temperature for each crop component. Potential growth of root and canopy had a 22 to 24°C optimum, whereas potential tuber growth had a 14 to 16°C optimum. Simulated leaf duration decreased as temperature increased. The model appropriately responded to temperature and solar radiation inputs to simulate cultivar Sebago growth in North Florida. In simulations, the most temperature sensitive yield parameter was TIO, with cool temperatures generally causing earlier TIO. Both M and NDMA were relatively insensitive to temperature with α having intermediate temperature sensitivity. Maximum simulated yield was at 15°C which corresponded with earliest TIO and maximum α. We conclude that temperatureffects on assimilate partitioning may be explained by differential temperature growth responses of potato crop components.

The aggressive and non-aggressive strains of Ceratocystis ulmi have different temperature optima for growth

The aggressive and non-aggressive strains of Ceratocystis ulmi exhibit markedly different temperature-growth responses in vitro . The optimum temperature of the aggressive strain (both EAN and NAN races) was 20–22°C and that of the non-aggressive strain was c. 30°. The upper limit for growth of the EAN aggressive was c. 32% of the NAN aggressive c. 33°, and of the non-aggressive strain c. 35° Two temperatures, 20 and 33°, are now recommended for separating the strains on the basis of growth-rate. The ranking order of the strains at 20° is the reverse of that at 33° and this provides a qualitative method for routine strain identification. The significance of the different temperature-growth responses of the two strains is discussed.