两种接种物对熊粪厌氧消化产沼气效果的影响

[目的]比较两种接种物对熊粪厌氧消化产沼气的效果。[方法]以熊粪为原料,采用不同的接种物(混合厌氧活性污泥和熊粪厌氧发酵结束后驯化所得的接种物),在30℃下进行了批量式恒温厌氧发酵,分析两种接种物对熊粪厌氧消化产沼气效果的影响。[结果]使用不同接种物的两组试验产气量存在差异,但相差不大;发酵时间存在较大差异,经过原料(熊粪)驯化的接种物发酵时间明显缩短,为沼气厌氧活性污泥发酵时间的1/3,且经过驯化的接种物具有更好的降解效果,能创造更好的适合于沼气发酵的中性环境。[结论]经过原料富集培养驯化的接种物具有更好的产沼气效果。     

黄瓜靶斑病菌接种体的繁殖

黄瓜靶斑病是近年来严重为害保护地黄瓜生产的一种新病害,为了促进靶斑病的抗病育种和防治,开展了12种固体和液体培养基配方、病菌移植方式、菌落颜色、光照条件、培养时间对黄瓜靶斑病菌繁殖效果的研究。结果表明,靶斑病菌菌落颜色深的菌株孢子产量大于菌落颜色浅的菌株;采用菌块涂抹法移植靶斑病菌效果最佳;繁殖靶斑病菌适宜的培养基为CZA120g,CZA80g,液体培养不适合靶斑病菌的繁殖;连续光照和黑暗处理对菌丝生长无显著影响,暗培养比光、暗交替和连续光照更有利于孢子的产生;28℃恒温、黑暗培养5 d是靶斑病菌产孢高峰期,分生孢子数量可达20.7×105个/mL。     

Effect of temperature and soil moisture on the survival and symbiotic effectiveness of Frankia spp.

Comparison of the effects of temperature on the growth in culture (increase in protein) of Frankia showed that three strains isolated from Casuarina were more tolerant of high temperature (45°C) than a strain from Alnus rubra. Optimal temperatures for growth of the Casuarina strains were in the range 25–30°C. Growth of the Alnus strain was good at 25°C but poor at 37°C. High temperatures (35–40°C) during storage for 7 months of these Frankia strains in sand, inoculated initially with liquid culture or with Frankia incorporated into alginate beads and permitted to dry, resulted in substantial loss of infectivity for the host plant species. Loss in infectivity was greater with an Alnus Frankia strain than strains from Casuarina cunninghamiana, C. equisetifolia and C. junghuniana. Three Frankia strains from C. equisetifolia were incorporated into a sand/perlite mixture with three different moisture regimes (field moisture capacity – wet: watered and maintained at field capacity; watered to field capacity but then allowed to dry – moderately wet; or watered to half field capacity and then permitted to dry – dry) and then stored for 12 weeks at 25°C and 35°C. Assessment by the most probable number (MPN) technique of the infectivity of the sand mixture for nodulation of C. equisetifolia showed significant interactions between Frankia strain, temperature and soil moisture content. The infectivity of Frankia strains ORS020607 and UGL020602q was not affected by incubation in wet sand at 25°C but fell by more than half after 12 weeks in moderate and dry conditions. Changes in infectivity were similar when incubation was at 35°C. By contrast, the infectivity of UGL020603q fell substantially under all moisture conditions and at both temperatures. The data show the importance of screening for tolerance of both temperature and moisture content when selecting strains for preparation of inoculum for use in hot climates. Received: 25 January 1996     

Improved immunological detection of S<Emphasis Type="Italic">pongospora subterranea</Emphasis>

The genus Spongospora has two members which are important pathogens of vegetables, S. subterranea f.sp. subterranea (Sss) and S. subterranea f.sp. nasturtii (Ssn). The close taxonomic relationship of these formae speciales is based on similar cystosori morphology. The potato disease powdery scab, caused by Sss, is difficult to control. The key control measure is avoidance, aimed at planting clean seed in clean soil. For the development of routine tests for the presence of the pathogen on tubers and in soil, a monoclonal antibody (MAb) was developed using Sss cystosori as immunogen. It detected less than one Sss cystosorus and recognised Sss material from many parts of the world. No cross-reactions with other Plasmodiophoromycetes including Plasmodiophora brassicae, Polymyxa betae, Polymyxa graminis and different Streptomyces species causing common and netted scab of potatoes were observed. A novel tuber sample test method was developed using a kitchen peeling machine. This detected two tubers with one powdery scab lesion each in a sample including eighteen uninfected tubers. When soil samples spiked with cystosori were tested with the MAb, different Sss infestation levels could be discriminated. Ssn cystosori gave absorbance values in ELISA as high as Sss cystosori, whereas fresh crook roots of watercress containing Ssnzoosporangia and plasmodia or mud from an Ssninfected watercress bed gave low absorbance values or no reaction. The potential of these findings for the development of a disease control management are discussed.     

Red pine harvest debris as a potential source of inoculum of Diplodia shoot blight pathogens

A high incidence of Diplodia shoot blight (site means ranging 85-100%) was observed on recently planted red pine (Pinus resinosa) seedlings where mature red pine stands previously had been clearcut. An investigation of the potential of harvest debris as a source of inoculum of Diplodia pathogens then was conducted. Cones, bark, needles, stems from shoots bearing needles, and stems from shoots not bearing needles (both suspended above the soil and in soil contact) were collected from harvest debris left at sites where clearcutting occurred. Conidia were quantified, and their germination rate was assessed, and Diplodia species were identified using PCR. Conidia of Diplodia species were found at all study sites and conidia counts increased from samples collected from 6 to 18 months after harvest. Germinable conidia were obtained from debris collected 6 months to 5 years after harvest. Fewer conidia were obtained from debris collected at intervals of up to 4-5 years after harvest and the percentage of germinable conidia was lower after longer intervals following harvest. More conidia were obtained and a greater percentage germinated from debris collected above the soil than from debris in soil contact. The host substrate also influenced the number of conidia and the percentage that germinated. Planting red pine seedlings next to debris infested with Diplodia pathogens could provide a persistent source of inoculum. Results should prompt further consideration by land managers and researchers of the potential forest health risks, in addition to benefits, that may be associated with harvest debris.     

Effect of phosphorus fertilization on blue-green algal inoculum production and nitrogen yield under field conditions

Summary Field experiments were conducted to assess the effects of the application of P on growth and N yield of inoculated and indigenous blue-green algae (BGA). Addition of 17.4 kg P ha^–1 in split applications led to the highest BGA biomass and N yield, 162 kg dry weight ha^–1 and 6 kg N ha^–1 per 15 days, respectively. When inoculum of Aulosira spp., Aphanothece spp., Gloeotrichia spp. were compared separately, Gloeotrichia spp. grew faster but Aulosira spp. fixed more N. The growth rate and N yield of Aulosira spp. decreased with high P applications, although growth continued until the application of 34.8 kg P ha^–1. The effects of P on inoculum production by local species compared with those collected from other states showed the superiority of the local culture. Applications of P also enhanced the growth and N yield of indigenous BGA, with Wollea spp. showing the best results.     

Assessment of arbuscular mycorrhizal fungal propagules and colonization from abandoned agricultural fields and semi-arid grasslands in riparian floodplains

Prior to the onset of extensive grazing and clearing for agriculture, riparian floodplains of southeastern Arizona, USA, historically supported large grassland communities dominated by Sporobolus wrightii Munro ex Scribn., big sacaton grass. Large-scale abandonment of agricultural operations has occurred in this region in the past 50 years, but natural re-establishment of big sacaton into abandoned fields has typically been slow. This study assesses whether arbuscular mycorrhizal fungi (AMF) may be one factor in recovery rates of abandoned fields within three riparian areas in southeastern Arizona (San Pedro river, the Babocomari river and Cienega creek). In each riparian area, soil samples were collected along paired 100 m transects, one in an extant grassland and one in a neighboring abandoned agricultural field. At one site (San Pedro), a third transect was established in a second adjoining abandoned agricultural field to enable comparisons between fields showing differing rates of recovery at a single site. Roots were assessed for mycorrhizal colonization using the modified intercept method and the modified mean infection percentage (MIP) method was used to determine inoculum potential of each soil sample. No significant differences were found between the levels of mycorrhizal colonization in roots collected from the grassland and those collected from the abandoned field for any of the sample sites. Levels of colonization did differ among the three sample sites, with higher levels seen at the San Pedro site than at the Babocomari and Cienega sites. With one exception, MIPs were greater in the soil from the abandoned agricultural field than in the soil from the nearby grassland. In the exception, no difference was detected in inoculum potentials at the San Pedro site between the paired grassland and the abandoned field that had the lower level of sacaton recovery. MIPs were also greater in the soil from the abandoned agricultural field at Babocomari, where Salsola tragus L. growth for cattle feed was promoted by discing every 3–4 years. These results indicate that higher inoculum potentials in abandoned fields were not always linked to the high levels of recovery of native vegetation.     

Effect of inoculum rate on the performance of chickpea (Cicer arietinum L.) Rhizobium strains in the field

Summary The influence of three inoculum rates on the performance of three chickpea (Cicer arietinum L.) Rhizobium strains was examined in the field on a Mollisol soil. Increasing amounts of inoculum improved the performance of the strains. A normal dose (10⁴ cells per seed) applied at different intervals gave non-significant increases in nodulation, nitrogenase activity (acetylene reduction assay), nitrogen uptake and grain yield. A ten-fold increase in inoculum increased nodule number, shoot dry weight, nitrogenase activity (ARA) and grain yield, but increases over the control were significant only for nodule dry weight and nitrogen uptake by shoot and grain. The highest level of inoculum (100 × normal) significantly increased nodule dry weight, grain yield, total nitrogenase activity (ARA) and nitrogen uptake by shoot and grain. Strain TAL 620 was more effective than the other two. Combined nitrogen (60 kg N ha^–1) suppressed nodulation and nitrogenase activity (ARA).Research paper No. 4345 from the Experiment Station, G. B. P. U. A. & T., Pantnagar, Nainital, U. P.     

Effect of environmental conditions on spore production by Fusarium verticillioides, the causal agent of maize ear rot

Silk infection by Fusarium verticillioides is caused by conidia produced on maize crop residues and results in kernel infection and consequent accumulation of fumonisins. Studies were carried out in both controlled and field conditions to understand the dynamics of sporulation on maize residues. The effect of temperature (5°C to 45°C) and incubation time (3 to 41 days) on spore production on maize meal agar was described by a logistic model that accounted for 85% of variability. The rate parameter depended on the length of incubation and the asymptote on temperature. Maximum sporulation occurred at 27°C, with a progressive increase between 5°C and 27°C and then a rapid decline, with no sporulation at 45°C. Fusarium verticillioides strains from different geographic origins showed different sporulation capabilities, with similar optimum temperatures. Pieces of stalk residues inoculated with F. verticillioides and placed above the soil between rows of maize crops, in 2003 to 2005, produced conidia continuously and abundantly for some weeks, particularly during the period after silk emergence, with an average of 1.59 × 10⁷ conidia g⁻¹ of stalk, over a wide range of environmental conditions. Sixty-seven percent of variability of the spore numbers found on stalks was accounted for by a multiple regression model. Precipitation (rain or overhead irrigation) in the 14 days before stalk sampling decreased the number of spores, whilst the number of days with conducive conditions of moisture (i.e. days with rainfall, average relative humidity >85% or vapour pressure deficit <4 hPa) and greater degree-days (base 0°C) in the 14 and 3 days before sampling, respectively, increased sporulation.     

Towards a more reasoned assessment of the threat to wheat crops from <Emphasis Type="Italic">Tilletia indica</Emphasis>, the cause of Karnal bunt disease

The interpretation of information used to defend an assessment that T. indica, the cause of Karnal bunt of wheat, has a high risk of establishing in Europe and of causing significant yield/quality losses is questioned. Karnal bunt has only established in locations that are arid or semi-arid with hot summers and cool/mild winters. There is very strong circumstantial evidence that substantial amounts of seed contaminated with teliospores of T. indica were sown in Europe in the past without the appearance of Karnal bunt. It is unlikely that sufficient numbers of teliospores would survive long enough on the soil surface under European conditions and then synchronise germination during the period at heading when wheat is vulnerable to infection to guarantee disease expression. Karnal bunt is regarded as a minor disease everywhere it occurs. Almost two thirds of European wheat cultivars inoculated by a severe boot injection method have been categorised as either resistant or highly resistant to T. indica. Yield/quality losses would be expected to be low even if the pathogen were capable of establishing in Europe. The status of T. indica as an important quarantine pest is based on the indirect economic consequences of the appearance of the pathogen and not on the direct damage it causes to wheat crops. Arguments in this and previous reviews advocating a more reasoned and comprehensive assessment of the threat to Europe, North America and other locations from T. indica need to be taken into consideration in any new pest risk analyses. David Jones is a retired employee of the Central Science Laboratory (CSL). Statements and opinions expressed in this paper are those of the author and are not the views of CSL.