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Physiological alterations in pepper during wilt induced by Phytophthora capsici and soil water deficit 总被引：2，自引：0，他引：2
Capsicum annuum cv. Morrón inoculated at the collar with Phytophthora capsici developed cortical stem necrosis and severe wilting soon after infection. Water potential, specific conductivity, ethylene evolution, CO2 and water vapour exchange rates and chlorophyll content were monitored during symptom development. Well watered and non-inoculated water-stressed plants were used as controls. Necrosis developed upwards from the collar 4 days after inoculation coupled with a 80% reduction in hydraulic conductivity. Leaf water potential progressively decreased from -0.17 to -2.41 MPa in 2 weeks. The rate of ethylene evolution was significantly higher in infected than in non-inoculated stressed plants for similar water potentials and originated in the necrotic segment of disease stem tissue. Net photosynthesis and leaf conductance markedly decreased (74%) 4 days after infection, coupled to a burst in dark respiration (1.5 times) but were not associated with water stress alone. This suggests that the pathogen reduced photosynthesis initially through stomatal closure which was not directly mediated by water stress. The possible implication of ethylene in impaired stem conductivity and altered gas exchange of infected plants is discussed. 相似文献
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Didymella rabiei grew saprophytically on pieces of infested chickpea stems and pods, and formed pycnidia and pseudothecia. The extent of saprophytic growth and production of viable spores were determined by the incubation conditions. On debris left on the soil surface under natural conditions, the fungus rapidly colonized the tissues, formed abundant pseudothecia and pycnidia, and remained viable throughout the 2 years of the study. When plant debris was buried, D, rabiei was restricted to the original lesions, in which it formed new pycnidia and was viable for 2 to 5 months. Under controlled conditions in the laboratory, D. rabiei extensively colonized plant debris spread over the soil surface. On the other hand, the fungus did not grow on buried debris, or showed only very limited development when the artificially infested debris was buried between two layers of sterilized soil. Incubation temperature was the principal factor associated with the production of conidia and especially ascospores. 相似文献
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Surface charge of mixtures of lepidocrocite and illite determined by adsorption of potential-determining and electrolyte ions is studied as a function of pH and NaCl concentration. Deviations between results obtained by both methods were a function of the illite content of the mixtures, and can be mainly attributed to coatings of hydroxyaluminium complexes on the constant charge surfaces of the clay mineral, which can react with H+ ions or release exchange sites by precipitation of well-formed hydroxides. These coatings of aluminium complexes can cause H+ consumptions similar to those due to lepidocrocite. Some ideas are put forward for modelling charge properties of mixed systems. 相似文献
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Optimization of the protein fraction of microcapsules used in feeding of marine fish larvae using in vitro digestibility techniques 总被引：1，自引：0，他引：1
The development of artificial feeds for marine fish larvae is demanding and, taking into account the difficulties and costs associated with the rearing of the larvae of some fish, preliminary evaluation of feed ingredients using in vitro techniques may be an alternative to in vivo assays. Some proteins used in microfeeds for marine fish were tested in vitro for examination of their effect on the proteases of seabream larvae. Casein and cuttlefish meal did not affect protease activity of crude larval extracts, whereas ovalbumin produced a 60% inhibition. The use of a pH-stat for the assessment of the degree of hydrolysis (DH) of proteins confirmed the low nutritive value of ovalbumin, since a much lower value was obtained for microcapsules prepared using this protein source when compared with those prepared using casein or cuttlefish meal (3.2 vs. 7.3 and 7.6, respectively). Products resulting from such hydrolysis were analysed using sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE). Image analysis of such gels led to the formulation of an index named the coefficient of protein degradation (CPD) which expressed the extent to which the main protein fractions were hydrolysed by larval proteases in a given time. A significant correlation ( r 2 = 0.98, P < 0.05) was obtained between DH and CPD values measured for either protein sources or microcapsules. The combination of protease inhibition assays with measurements of DH and CPD is proposed as a preliminary evaluation of protein ingredients used in the formulation of artificial feeds for larval fish. 相似文献
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Melissa PLASMAN Amando BAUTISTA Marshall D. McCUE Aníbal H. DÍAZ DE LA VEGA‐PREZ 《Integrative zoology》2020,15(5):363-374
Individuals that inhabit broad elevational ranges may experience unique environmental challenges. Because temperature decreases with increased elevation, the ectotherms living at high elevations have to manage limited activity time and high thermoregulatory effort. The resting metabolic rate (RMR) of a postabsorptive animal is related to its total energy requirements as well as many other fitness traits. Mesquite lizards (Sceloporus grammicus) living on La Malinche Volcano, Mexico, inhabit a wide elevational range with some populations apparently thriving above the tree line. We measured the RMR of lizards from different elevations (i.e., 2,600, 3,200, and 4,100 m) at four ecologically relevant temperatures (i.e., 15, 25, 30, and 35 °C) and found that RMR of mesquite lizards increased with temperature and body mass. More importantly, lizards from the high‐elevation population had mass specific RMR that was higher at all temperatures. While the higher RMRs of high‐elevation populations imply higher metabolic costs at a given temperature these lizards were also smaller. Both of these traits may allow these high elevation populations to thrive in the face of the thermal challenges imposed by their environment. 相似文献
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Leroy SORIA‐DÍAZ Mike S. FOWLER Octavio MONROY‐VILCHIS Daniel ORO 《Integrative zoology》2018,13(1):84-93
The study of predator–prey interactions is commonly analyzed using functional responses to gain an understanding of predation patterns and the impact they have on prey populations. Despite this, little is known about predator–prey systems with multiple prey species in sites near the equator. Here we studied the functional response of cougars (Puma concolor) in relation to their main prey, armadillo (Dasypus novemcinctus), coati (Nasua narica) and white‐tailed deer (Odocoileus virginianus). Between 2004 and 2010, cougar scats were collected along 5 transects to estimate the consumption of different prey species. A relative abundance index (RAI) was calculated for each prey species and cougar using 18 camera traps. We compared Holling type I, II and III functional response models to determine patterns in prey consumption based on the relative abundance and biomass of each prey species consumed. The 3 main prey species comprised 55% (armadillo), 17% (coati) and 8% (white‐tailed deer) of the diet. Type I and II functional responses described consumption of the 2 most common prey species armadillos and coati similarly well, while a type I response best characterized consumption of white‐tailed deer. A negative correlation between the proportions of armadillo versus coati and white‐tailed deer biomass in cougar scats suggests switching to consume alternative prey, confirming high foraging plasticity of this carnivore. This work represents one of the few studies to compare functional responses across multiple prey species, combined with evidence for prey‐switching at low densities of preferred prey. 相似文献
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A survey of weeds and weeding practices was carried out by a team of agricultural economists and agronomists on 283 farms in five Cassava growing regions of Colombia at three times during a cropping season. Seventy-one to 78% of all weed species present were broadleaved species. As cassava grew older, grass species were present to a greater and sedge species to a lesser relative frequency. Surprisingly Pteridiumaquilinum (L.) Kuhn was the most frequently listed species and Bidens pilosa L. and Cyperus rotundus L. were other frequent problems. Regional variations in the most frequently encountered species were found but several of the weeds were common to many zones. The most frequently encountered species did not usually have the highest plant populations. Most of the annual grasses, sedges and broadleaf weeds found can be controlled by currently recommended herbicides for cassava but further research is needed on Imperata cylindrica (L) Beauv., Melinis minutlftora Beauv., P. aquilinum and Sida spp. The average number of manual weedings was 3.3 per crop, occupying 48 man-days/ha which is 50% of the total labor requirements for cassava production, and more than one-third of the total costs. Reasons for not using herbicides were (1) relative costs of herbicides and labor. (2) lack of information, (3) lack of capital, (4) right herbicides were not available, and (5) herbicides were not available in small packages. This survey has usefully identified new field problems and has suggested further research programs to solve them. 相似文献
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