Effect of irrigation on the dynamics of Phytophthora citrophthora populations in soil of citrus orchards1

Effects of irrigation on the dynamics of soil populations of Phytophthora citrophthora have been studied in three citrus orchards in East Sicily (Italy). Significant increases of inoculum levels were detected 24 h after irrigation. In one orchard throughout summer, population of P. citrophthora beneath the tree canopy was more than 15 propagules g-¹ soil, a value which is considered a threshold level for root rot infections.     

Detection of Phytophthora nicotianae and P. citrophthora in Citrus Roots and Soils by Nested PCR

The polymerase chain reaction (PCR) was used for the specific detection of Phytophthora nicotianae and P. citrophthora in citrus roots and soils. Primers were based on the nucleotide sequences of the internal transcribed space regions (ITS1 and ITS2) of 16 different species of Phytophthora. Two primer pairs, Pn5B–Pn6 and Pc2B–Pc7, were designed specifically to amplify DNA from P. nicotianae and P. citrophthora, respectively. Another primer pair (Ph2–ITS4) was designed to amplify DNA from many Phytophthora species. All primer pairs were assessed for specificity and absence of cross-reactivity, using DNA from 118 isolates of Phytophthora and 82 of other common soil fungi. In conventional PCR, with a 10-fold dilution series of template DNA, the limit of detection was of 1pgl^–1 DNA for all the primer pairs (Ph2–ITS4, Pn5B–Pn6, and Pc2B–Pc7). In nested PCR, with primers Ph2–ITS4 in the first round, the detection limit was of 1fgl^–1 for both the primer sets (Pn5B–Pn6 and Pc2B–Pc7). Simple, inexpensive and rapid procedures for direct extraction of DNA from soil and roots were developed. The method yielded DNA of a purity and quality suitable for PCR within 2–3h. DNA extracted from soil and roots was amplified by nested PCR utilizing primers Ph2–ITS4 in the first round. In the second round the primer pairs Pn5B–Pn6 and Pc2B–Pc7 were utilized to detect P. nicotianae and P. citrophthora, respectively. Comparison between the molecular method and pathogen isolation by means of a selective medium did not show any significant differences in sensitivity.     

Studies on the persistence of the organotin fungicide fentin acetate (triphenyltin acetate) in the soil and on surfaces exposed to light

The results of a study into the persistence of triphenyltin (=fentin) acetate in soil are presented. The fungicide is degraded biologically 50% being decomposed in 140 days. The photochemical degradation of fentin acetate into inorganic tin via diphenyltin and monophenyltin compounds also is demonstrated. The leaching of fentin acetate in soil and its effect on soil nitrification is discussed.     

Antifeeding and protease- and amylase-inhibiting activity of fentin acetate in Spodoptera littoralis larvae

Fentin acetate (FA) at effective antifeedant concentrations does not have a high, immediate toxicity for 170–190 mg larvae of the Egyptian cotton leafworm (Spodoptera littoralis); the mortality of such larvae exposed to FA residues on leaves is not appreciably higher than that of larvae being starved. The antifeedant effect of FA is also not due to an influence on sensory receptors on the mouth parts. Protease and amylase are inhibited in vivo in larvae feeding on FA-treated leaves; the enzyme inhibition increases with the concentrations of the leaf-dipping suspensions. At 0.05% FA, protease and amylase activity was only about 20 and 30%, respectively, of that of the control larvae and was lower than in starved larvae.Antifeeding and enzymatic inhibition are also obtained by injecting FA into the haemocoel, results which indicate that FA does not inhibit the digestive enzymes directly, but seems to affect the enzyme production in the gut. This interpretation is strengthened by the finding that the addition of massive amounts of FA to the enzyme reaction mixture does not affect the enzyme activity.     

Uptake and utilisation of phosphonate ions by Phytophthora citrophthora and Nectria haematococca in relation to their selective toxicity

Phosphonate ions, which are degradation products of aluminium tris-O-ethyl phosphonate (fosetyl-aluminium) in plant tissues, had more effect in vitro against Phytophthora citrophthora than against Nectria haematococca. Both fungi were able to take up phosphonate ions. This uptake was realised against a concentration gradient and was affected by metabolic inhibitors. When examined over a 0.5 to 6.0 mm concentration range, phosphonate was carried by a single transport process obeying Michaelis-Menten kinetics, with a low affinity (high K′_m). Further analysis by means of Hofstee plots indicated a somewhat faster phosphonate uptake by N. haematococca than by P. citrophthora, so it appears clearly that uptake was not involved in the selective toxicity of this compound. The continuous uptake of phosphonate by N. haematococca is correlated with an important utilisation of this ion by the fungal cells. This fact could be explained by a detoxification process corresponding to the oxidation of phosphonate to phosphate which could account for the low sensitivity of this fungus. Phosphonate uptake by P. citrophthora reached a maximum level after 20 min and then decreased to a constant level over the following period. During the incubation period phosphonate was incorporated directly without oxidation into phosphate. This incorporation could lead to a disturbance of the cell metabolism.     

Role of the Helix aspersa snail as a vector of Phytophthora citrophthora causing branch cankers on clementine trees in Spain

This study investigated the suspected role of invertebrate vectors in the transmission of phytophthora branch canker, a severe disease of clementine cultivars in Spain, caused by Phytophthora citrophthora . Ants ( Lasius grandis ) and snails ( Helix aspersa and Rumina decollata ) were collected in spring and autumn 2005 from 15 commercial citrus fields which were severely affected by the disease. Isolations made from L. grandis and R. decollata bodies did not yield positive results. However, P. citrophthora was isolated from 5·0% of bodies of H. aspersa and 4·8% of samples of their faeces. In one assay, after snails were allowed to feed for 5 h on citrus branches which had been artificially infected with P. citrophthora , the pathogen was isolated from 79% of their faeces. In another experiment, snails were infested by placing them in contact with a substrate colonized by P. citrophthora and then transferred to the base of potted 4-year-old trees of cvs Clemenules, Fortune and Nova in the glasshouse. One day after their release, infested snails were widely distributed throughout the tree canopies and 10 days later bark discoloration and gum exudations were observed on the trees. Phytophthora citrophthora was readily isolated from tissues showing symptoms.     

韩城市花椒园土壤养分状况及施肥研究

根据大量土壤样品的分析结果及调查资料，研究了陕西省韩城地区花椒园土壤养分状况、施肥结构和变化趋势。结果表明，供试的180个花椒园施肥量和土壤养分含量变异很大。总体上看，土壤有机质、钾素不足；氮素处于中等水平；磷素较为丰富；微量元素锌、硼、钼极度缺乏；营养元素比例失调，肥料利用率偏低，整体肥力水平低。提出优化施肥结构，增施有机肥、钾肥和微肥，提高花椒产量和品质。     

Distribution and breakdown of DDT in orchard soil

Amounts of DDT and its breakdown products were determined in soil in an apple orchard in Herefordshire. Samples were taken for a number of years (1972–79) after use of the insecticide in the orchard had ceased in 1969. The results were compared with those obtained in an investigation of the same orchard in 1968. From 1968 to 1979, soil residues of pp′-DDT, p′--DDT and pp′--TDE decreased gradually whereas those of pp′--DDE increased, and there were linear relationships between log (concentration) and time. The calculated time for 50% decrease in concentration (Dt₅₀) was 11.7 years for pp′--DDT, 3.3 years for pp′--TDE and 7.1 years for op′--DDT; the time for doubling the concentration for pp′--DDE was 9.1 years. Regression analysis on the two major components (pp′--DDT+pp′--DDE) indicated that the total amount (2.7 mg kg^?1) was not decreasing with time. It was concluded that during a post-spray era, the breakdown of pp′--DDT to pp′--DDE was a significant feature of the persistence of DDT, and that, in contrast to the findings of other workers who sampled when DDT was being used, there were no losses by volatilisation. There was an exponential decrease in the amount of DDT residues with increasing soil depth and approximately 90% was found in the top 10 cm of the undisturbed soil profile.     

Air-assisted sprayers for application in vine,orchard and similar crops1

Spraying in so-called space cultures (orchards, vineyards) is determined by two main aims which require contrary technical measures for their realization: (1) optimal even distribution of droplet deposition on the target. This generally requires sufficient air assistance of droplet transportation and penetration in order to bridge the distance between the nozzle outlet and the target; (2) the surplus energy which normally exists should be minimized in order to avoid any droplet flow outside the target. Several possibilities exist to approach these requirements: (1) optimal blower design and correct adjustment for each specific purpose; (2) catching and recycling of misdirected droplets by recycling units; (3) sensoring of gaps in the canopy and activation of a nozzle shut-off. The legal requirements of the BBA are given, together with the results of experiments on drift and ground deposition of chemicals from air-assisted sprayers, with special attention to recycling units and sensored sprayers.     

渭北高原不同施肥方案土壤效应及对再植苹果生长发育的影响

为了给通过施肥解决苹果连作障碍问题提供借鉴,于2006～2007年在西北农林科技大学白水苹果试验站,采用盆栽试验和大田试验,研究了施用磷肥和抗重茬肥对土壤养分、微生物、土壤酶以及幼树根系活力、株高、叶面积的效应.结果表明:施用500 g/株抗重茬肥可以提高土壤有效养分和土壤酶,改善土壤微生物群体结构,促进植株生长,与非连作幼树表现基本一致;施用250 g/株抗重茬肥、500 g/株和1 000 g/株磷肥在减轻连作危害方面效果较好,处理后多数测定指标都相对高于连作幼树对照,但效应有限.综合考虑土壤效应和苹果生长因素,老果园再植以施用500 g/株用量的抗重茬肥可以部分解决苹果再植障碍问题.     

Evaluation of selective media and bait methods for estimating Phytophthora cactorum in apple orchard soils

Soil plating, with a specially devised selective medium, gave estimates of Phytophthora cactorum in an East Mailing Research Station apple orchard soil up to three times those obtained by dilution and baiting with apple seedlings or cotyledons and using the most probable number analysis.
When the same techniques were applied to a range of soils from apple orchards in south-east England with a history of P. cactorum diseases the plating method failed in most instances, mainly because Pythium spp. rapidly swamped the plates. The dilution/baiting method was applicable to all soils though there was a tendency to underestimate because of anomalous results at lower soil dilutions.
Oospores were the only propagules which could be confirmed as sources of P. cactorum colonies on soil isolation plates.     

Development of a species-specific and sensitive detection assay for Phytophthora infestans and its application for monitoring of inoculum in tubers and soil

A specific and sensitive PCR assay for the detection of Phytophthora infestans , the cause of late blight of potato, in soil and plant tissues was developed. A P. infestans -specific primer pair (INF FW2 and INF REV) was designed by comparing the aligned sequences of rDNA internal transcribed spacer regions of most of the known Phytophthora species. PCR amplification of P. infestans DNA with primers INF FW2 and INF REV generated a 613 bp product, and species specificity was demonstrated against DNA from nine other Phytophthora species and seven potato-blemish pathogens. In a single-round PCR assay, 0·5 pg pure P. infestans DNA was detectable. Sensitivity was increased to 5 fg DNA in a nested PCR assay using Peronsporales-specific-primers in the first round. As few as two sporangia or four zoospores of P. infestans could be detected using the nested assay. Procedures are described for detection of P. infestans in leaves, stem and seed potato tubers before expression of symptoms. A soil assay in which 10 oospores per 0·5 g soil were detectable was developed and validated using samples of field soil. The PCR assay was used to examine the long-term survival of sexual (oospores) and asexual (sporangia and mycelium) inoculum of P. infestans in leaf material buried in a replicated experiment under natural field conditions. Oospores were consistently detected using the PCR assay up to 24 months (total length of the study) after burial in soil, whereas the sporangial inoculum was detected for only 12 months after burial. Sporangial inoculum was shown to be nonviable using a baiting assay, whereas leaf material containing oospores remained viable up to 24 months after burial.     

果园生草栽培技术的研究与应用

果园生草栽培是在果园种植(保留)草本植物作为覆盖物的一种果园管理方法。生草栽培的草种可以是一种或混合多种,模式有全园生草、带状(行间或株间)生草两种;方式有三种,一是自然生草,指在剔除恶性杂草的基础上,利用果园的自然杂草进行生草栽培;二是人工种草,指选择适宜草种在果园人工种植;三是在自然生草基础上,增加人工种草[1]。果园生草于19世纪末始见于美国,20世纪40年代随着割草机的问世和灌溉系统的发展而得到推广[2]。目前,欧美和日本等发达国家六成以上的果园采用了生草栽培技术,而我国生草栽培果园面积比例还不到一成[3-4]。为加快果园生草栽培技术在广西全面推广应用,推进农药使用量零增长行动,笔者通过查阅文献、果园观察和走访调研,对果园生草栽培技术的研究与应用进行综述,据此提出广西发展果园生草栽培的策略。     

沼液不同施用方式对苹果园土壤及叶片养分和果实品质的影响

陕西目前苹果种植面积位于全国第一,但果园存在的最大问题是基础肥力低,有机肥肥源和施用不足。为探讨沼液作为有机肥在苹果上的合理施用技术,本试验采用叶面喷施、灌施、树干涂抹3种方式进行了沼液在铜川苹果园施用效果的研究,分析了3种施用方式和不同施用量对叶片和土壤养分含量及果实品质的影响。结果表明,幼龄果树和盛果期树每株分别灌施沼液30 kg、60 kg对叶片和土壤养分含量及果实品质影响显著,和对照相比,叶片氮、磷、钾含量分别增加15.66%、134.91%、45.83%(幼龄树)和5.59%、12.43%、28.65%(盛果期树),幼龄树和盛果期树的果实可溶性固形物分别增加了31.33%、27.38%,Vc含量分别增加了53.67%、50.92%。幼龄树喷施1∶2沼液和盛果期树喷施1∶1的沼液效果较好,树干涂抹沼液对叶片营养和果实影响较小。     

灌溉和生草对猕猴桃园土壤质量的影响

为探明灌溉和生草对猕猴桃园土壤质量的影响,于2016—2017年在陕西省眉县猕猴桃园试验地分别布设地面灌溉+除草(Ⅰ)、地面灌溉+自然生草(Ⅱ)、滴灌+除草(Ⅲ)和滴灌+自然生草(Ⅳ)4种处理,对试验地0～50 cm土层的土壤机械组成、物理和化学性质进行了统计分析,并利用土壤质量综合指数对土壤质量进行了评价,结果表明:与其他处理相比,Ⅲ处理使0～30 cm土层土壤容重和砂粒质量分数分别降低了0.02～0.24g·cm~(-3)和0.36%～5.25%,使土壤孔隙度、田间持水量、黏粒质量分数和土壤粒径分形维数分别增大了0.17%～7.17%、0.59%～2.53%、0.99%～7.15%和0.01～0.13;Ⅳ处理在0～30 cm土层中的速效磷和碱解氮与Ⅰ、Ⅱ处理无差异,显著高于Ⅲ处理10.75～109.55 mg·kg~(-1)和20.74～78.91 mg·kg~(-1)(P0.05),可使0～50 cm土层的速效钾、速效磷和碱解氮分别达到猕猴桃施肥标准的丰富、中等及中等水平;与其他处理相比,Ⅳ处理可使0～50 cm土层土壤黏粒质量分数增加了1.21%～2.66%,土壤粉粒质量分数减少了0.81%～1.41%,使土壤分形维数显著增加(P0.05),土壤质量综合指数最大,达0.619。因此,滴灌+自然生草(Ⅳ)的管理方式是猕猴桃园土地可持续性利用的有效措施。     

不同覆草量苹果园土壤水温效应及对树体生长的影响

将麦草覆盖应用于果园,研究不同覆盖用量22 000 kg·hm-2(T1)、33 000 kg·hm-2(T2)、44 000 kg·hm-2(T3)和清耕(CK)在整个生长期对19年生长富2号苹果园0~100 cm土壤水分、5~25 cm土壤温度、树体生长量及果实品质的影响。结果表明:在旱情较重的4—7月,3种覆草处理的平均含水量随覆草量的增加而增大,其中T2和T3处理极显著(P0.01)高于CK,高出8.98%~27.09%;且3种覆草处理0~20、20~40 cm土层的含水量极显著(P0.01)高于CK,高出9.36%~73.77%;4—8月3种覆草处理的各深度地温低于CK,4—6月份极显著(P0.01)低于CK,低出2.11℃~8.02℃;相反,9—11月份高于CK。覆草处理5~20 cm深度土温日变幅极显著(P0.01)低于CK,低出0.39℃~3.63℃。果实单果重和产量以T2处理最高,3种覆草处理每公顷产量较CK极显著(P0.01)提高,高出10.70%~20.83%;产量水分利用效率覆草处理较CK极显著(P0.01)增高,高出9.87%~20.87%。覆草对树体生长量、枝类比例影响不大。综合各种效应及投入产出比,陇东黄土高原苹果园覆草量以22 000~33 000 kg·hm-2较经济适宜。     

Effect of propiconazole on substrate amended soil respiration following laboratory and field application

The effect of the fungicide propiconazole (‘Tilt’^TM 250 EC) on substrate-amended soil respiration has been studied in dose-response experiments, following application of the compound in the field and in the laboratory. The field study was supplemented with spray-deposition measurements showing a throughfall at the soil surface of 15-45%, depending on the time of fungicide application. When propiconazole was amended to the soil in low dosages in laboratory conditions, the soil respiration was stimulated. Even at the very high and agriculturally unrealistic dosages in the laboratory experiment, the mean, daily soil respiration almost recovered within the incubation period of 30 days. Given the present conditions, the results did, however, also show that side-effects of the application of the fungicide were provoked at lower dosages in the field, and that they lasted for a considerably longer time than in the laboratory, indicating the importance of indirect effects of fungicide application in field conditions. Possible reasons for the dose-response relationship in the field being different from the one found in the laboratory are discussed.     

Physiological alterations in pepper during wilt induced by Phytophthora capsici and soil water deficit

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.