Single-strand-conformation polymorphism of ribosomal DNA for rapid species differentiation in genus Phytophthora

Single-strand-conformation polymorphism (SSCP) of ribosomal DNA of 29 species (282 isolates) of Phytophthora was characterized in this study. Phytophthora boehmeriae, Phytophthora botryosa, Phytophthora cactorum, Phytophthora cambivora, Phytophthora capsici, Phytophthora cinnamomi, Phytophthora colocasiae, Phytophthora fragariae, Phytophthora heveae, Phytophthora hibernalis, Phytophthora ilicis, Phytophthora infestans, Phytophthora katsurae, Phytophthora lateralis, Phytophthora meadii, Phytophthora medicaginis, Phytophthora megakarya, Phytophthora nicotianae, Phytophthora palmivora, Phytophthora phaseoli, Phytophthora pseudotsugae, Phytophthora sojae, Phytophthora syringae, and Phytophthora tropicalis each showed a unique SSCP pattern. Phytophthora citricola, Phytophthora citrophthora, Phytophthora cryptogea, Phytophthora drechsleri, and Phytophthora megasperma each had more than one distinct pattern. A single-stranded DNA ladder also was developed, which facilitates comparison of SSCP patterns within and between gels. With a single DNA fingerprint, 277 isolates of Phytophthora recovered from irrigation water and plant tissues in Virginia were all correctly identified into eight species at substantially reduced time, labor, and cost. The SSCP analysis presented in this work will aid in studies on taxonomy, genetics, and ecology of the genus Phytophthora.     

Use of a bioassay to evaluate the toxicity of beauvericin to bacteria

An agar diffusion bioassay was used to compare the sensitivities of bacteria to the mycotoxin beauvericin. Bacillus pumilus LACB101 was inhibited by filter-paper disks containing 0.1 g of beauvericin; B. cereus, B. mycoides, B. sphaericus, Paenibacillus alvei, P. azotofixans, P. macquariensis, and P. pulvifaciens by 1 g; and P. validus by 25 g. The anaerobes Eubacterium biforme, Peptostreptococcus anaerobius, P. productus, Bifidobacterium adolescentis, and Clostridium perfringens were also inhibited by beauvericin.     

三种猕猴桃根腐病致病菌多重实时定量PCR检测技术的建立及应用

[背景]近年来,随着猕猴桃种植面积的不断扩大,病害的频繁发生已逐渐影响猕猴桃的产量和品质。恶疫霉(Phytophthora cactorum)、樟疫霉(P.cinnamomi)和雪松疫霉(P.lateralis)是一类可以引起猕猴桃根腐病的致病疫霉菌。[目的]建立并优化可以同时检测3种致病疫霉的多重实时定量检测技术,并调查猕猴桃主要产区的致病菌分布情况。[方法]基于Ypt1 (ras-related protein gene)基因设计恶疫霉、樟疫霉和雪松疫霉的特异性TaqMan探针和引物,建立并优化多重实时荧光定量PCR检测体系。利用近缘种检验检测体系特异性并进行灵敏度测试,应用该检测体系分析猕猴桃主要产区根际土壤中3种致病疫霉的Yt1基因含量。[结果]供测试的11个恶疫霉近缘种、11个樟疫霉近缘种、13个雪松疫霉近缘种及非目标菌种DNA样品中均无荧光信号,反应结果为阴性,而在恶疫霉、樟疫霉和雪松疫霉DNA样品中分别检测出HEX、FAM和ROX荧光信号,反应结果为阳性。三种疫霉的检测灵敏度均达到100fg。此外,通过对猕猴桃主产区陕西省周至县和眉县果园共166份土壤样品的检测发现,恶疫霉的分布最广泛且Ypt1基因含量最高,樟疫霉和雪松疫霉则相对较少。[结论]建立的猕猴桃根腐病致病疫霉多重实时定量检测体系特异性强、灵敏度高,适合于恶疫霉、樟疫霉和雪松疫霉的检测及定量分析。该技术可为猕猴桃疫霉病害的早期诊断、监测及预防提供指导。     

The synthesis of photorubin in yeasts: Relationships with a diazotable amine

Summary Photorubin, the light-dependent water-soluble pigment formed by Saccharomyces cerevisiae var. ellipsoideus, is in close relationship with a diazotable amine absorbing at 540 m after the Bratton-Marshall reaction.The culture liquids of the photorubin-negative strains (deficient in histidine synthesis) obtained by hybridization do not contain diazotable amines and have only one peak at 248 m in their ultraviolet absorption spectra. Back mutants to photorubin-positivity and the wild type do contain diazotable amines and or have only one peak at 282 m.The addition of p-aminobenzoic acid to the growth medium reduces photorubin formation, whereas histidine exerts the opposite effect.     

Polysaccharides of <Emphasis Type="Italic">Pseudomonas</Emphasis> Pathovar Strains That Infect Pea,Tomato, and Soya Bean

In order to understand the mode of action of taxonomically related Pseudomonas syringae pathovar strains that infect pea, tomato, and soya bean, we examined their extracellular polysaccharides (EPS). Maximum production of polysaccharide in shake culture of these pathogens was observed between 24 and 60 h. P. syringae pv. pisi 519, the bacterial blight pathogen of pea, produced a higher amount of polysaccharide (34.87 g/mL) at 60 h compared with 32.67 g/mL produced by P. syringae pv. glycinea NCPPB 1783, the bacterial blight pathogen of soya bean, and 30.03 g/mL produced by P. syringae pv. tomato NCPPB 269, the bacterial speck pathogen of tomato. EPS produced by P. syringae pv. pisi 519, P. syringae pv. tomato NCPPB 269, and P. syringae pv. glycinea NCPPB 1783 was characterized with infrared (FTIR), nuclear magnetic resonance (NMR), high performance thin layer chromatography, (HPTLC), and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. HPTLC profiles revealed the presence of glucose and glucuronic acid in all bacteria and mannose only in P. syringae pv. tomato. Molecular mass of EPS of P. syringae pv. pisi (m/z 933.8), P. syringae pv. tomato (m/z 950.4), and P. syringae pv. glycinea (m/z 933.5) was confirmed by MALDI-TOF mass spectrometry.     

Antagonism of Chaetomium globosum, Gliocladium virens and Trichoderma viride to four soil-borne Phytophthora species

Chaetomium globosum, Gliocladium virens and Trichoderma viride, isolated from soil samples from the Kivu-region of Zaire, are antagonistic and mycoparasitic to four soil-borne Phytophthora spp. Radial growth of Phytophthora cinnamomi, P. cactorum, P. fragariae or P. nicotianae mycelia was inhibited in all antagonist-pathogen combinations; mycelial mats of Phytophthora colonies were overgrown by the antagonists and hyphae lysed. Samples of mycoparasited mycelium, plated on benlateamended PDA to inhibit the development of antagonists, showed severely reduced vitality after 77 days of dual culture.     

Evaluation of Resistance of Stone Fruit Rootstocks to Phytophthora Crown Rot*

The pathogenicity of Phytophthora citrophthora, Phy‐tophthora cactorum and Phytophthora megasperma strains was confirmed on 2‐year‐old stone fruit rootstocks artificially inoculated in the field. Phytophthora mega‐sperma was not virulent or less virulent than P. cactorum or P. citrophthora. The rootstocks Damas and AN 1/7 were resistant whereas the rootstocks Jl, Titan x Nemaguard 5/1, GF 677, Myrandier 613, Italian x Nemaguard 1 and Myrandier 617 were susceptible to P. citrophthora. The rootstocks Tsukuba 9, Tit‐an x Nemaguard 4/7, AN 1/2, AN 1/3, St. Mien 655/2 and Bl showed medium susceptibility to this species. The isolates of P. cactorum induced more extensive necrosis in Myrandier 617 and Italian x Nemaguard than in Myr‐andier 613, GF 677, Jl (ADAFUEL), Tsukuba 9 and St. Julien 655/2. Among seven rootstocks, Tsukuba 5 and St. Julien 655/2 were more resistant than Myrandier 613, Myrandier 617, Jl (ADAFUEL), Tsukuba 9 and St. Julien 655/2.     

Growth responses ofPterocladiella capillacea(Rhodophyta) in laboratory and outdoor cultivation

The growth and photosynthetic responses ofPterocladiella capillaceato NH₄, PO₄, CO₂-enrichment, pH, irradiance and temperature were evaluated for winter or summer plants cultivated under laboratory and outdoor settings. In the laboratory, using a gradient table, optimal growth temperature and irradiance for winter plants occurred at 10–20 °C and 100 mol photon m^–2s^–1, averaging 24.3% per week. The optimal growth conditions found for summer plants were 10–20 °C and 20 mol photon m^–2s^–1, averaging 29.0% per week. In a pH-stat cultivation system photosynthetic rates and growth rates were largely unaffected by pH in the range 6.5–8.5, however, they both decreased significantly above 8.5. In outdoor settings, using 40 L tanks,P. capillaceawas more responsive to the frequency the algae were fed with NH₄and PO₄rather than the relative concentrations of these nutrients. The average growth rates during winter were 28.3% and 12.5% per week when NH₄and PO₄were included once and twice a week for 24-h periods, respectively, while summer plants grew 15.0% and 25.3% per week at these nutrient regimes. Algae grown in seawater (containing 13.8 ± 1.8 M CO₂) or CO₂-enriched seawater (averaging 33.7 ± 13.2 M CO₂) had similar growth rates or even reduced productivity under CO₂-enrichment during winter. Concentrations of chlorophyllawere in average significantly higher in winter as compared to summer especially when nutrients were included twice a week. Phycoerythrin levels were also higher for plants fed with nutrients twice a week particularly during summer time. Although agar yields were limited and not seasonally dependent, this study shows high growth capacity forP. capillaceaas compared to previous investigations. Future mariculture prospective using current tank cultivation techniques for this species will likely depend on market demands for high quality agar.     

Effects of external phosphorus supply on internal phosphorus concentration and the initiation,growth and exudation of cluster roots in Hakea prostrata R.Br.

The response of internal phosphorus concentration, cluster-root initiation, and growth and carboxylate exudation to different external P supplies was investigated in Hakea prostrata R.Br. using a split-root design. After removal of most of the taproot, equal amounts of laterals were allowed to grow in two separate pots fastened together at the top, so that the separate root halves could be exposed to different conditions. Plants were grown for 10 weeks in this system; one root half was supplied with 1 M P while the other halves were supplied with 0, 1, 25 or 75 M P. Higher concentrations of P supplied to one root half significantly increased the P concentration of those roots and in the shoots. The P concentrations in root halves supplied with 1 M P were invariably low, regardless of the P concentration supplied to the other root half. Cluster root initiation was completely suppressed on root halves supplied with 25 or 75 M P, whereas it continued on the other halves supplied with 1 M P indicating that cluster-root initiation was regulated by local root P concentration. Cluster-root growth (dry mass increment) on root halves supplied with 1 M P was significantly reduced when the other half was either deprived of P or supplied with 25 or 75 M P. Cluster-root growth was favoured by a low shoot P status at a root P supply that was adequate for increased growth of roots and shoots without increased tissue P concentrations. The differences in cluster-root growth on root halves with the same P supply suggest that decreased cluster-root growth was systemically regulated. Carboxylate-exudation rates from cluster roots on root halves supplied with 1 M P were the same, whether the other root half was supplied with 1, 25 or 75 M P, but were approximately 30 times faster when the other half was deprived of P. Estimates of root P-uptake rates suggest a rather limited capacity for down-regulating P uptake when phosphate was readily available.     

Two Widely Accessible Media for Growth and Reproduction of Phytophthora and Pythium Species

Tomato agar and soybean agar were found to be comparable to or in some cases better than the popular V8 vegetable juice agar in supporting linear growth of Phytophthora cactorum, Phytophthora capsici, Phytophthora parasitica, Pythium aphanidermatum, and Pythium splendens; sporangium production of P. capsici, P. palmivora, and Pythium splendens; and oospore formation of P. cactorum, P. parasitica, Pythium aphanidermatum and Pythium splendens. These two media with readily accessible ingredients can be used to substitute for V8 juice agar in pathological and physiological studies of these two important groups of fungi in countries where V8 vegetable juice is not available or difficult to obtain.     

Viral diversity in Phytophthora cactorum population infecting strawberry

Eighty-eight Phytophthora cactorum strains isolated from crown or leather rot of strawberry in 1971–2019 were screened for viruses using RNA-seq and RT-PCR. Remarkably, all but one isolate were virus-infected, most of them harbouring more than one virus of different genera or species. The most common virus occurring in 94% of the isolates was the Phytophthora cactorum RNA virus 1 (PcRV1) resembling members of Totiviridae. Novel viruses related to members of Endornaviridae, named Phytophthora cactorum alphaendornaviruses 1-3 (PcAEV1-3), were found in 57% of the isolates. Four isolates hosted viruses with affinities to Bunyaviridae, named Phytophthora cactorum bunyaviruses 1-3 (PcBV1-3), and a virus resembling members of the proposed genus ‘Ustivirus’, named Phytophthora cactorum usti-like virus (PcUV1), was found in a single isolate. Most of the virus species were represented by several distinct strains sharing ≥81.4% aa sequence identity. We found no evidence of spatial differentiation but some temporal changes in the P. cactorum virus community were observed. Some isolates harboured two or more closely related strains of the same virus (PcAEV1 or PcRV1) sharing 86.6%–96.4% nt identity in their polymerase sequence. This was surprising as viruses with such a high similarity are typically mutually exclusive.     

Identification and expression of the Pseudomonas syringae pv. aptata hrpZPsa gene which encodes an harpin elicitor

A sequence homologous to an internal fragment 0.75 kb BstXI of the Pseudomonas syringae pv. syringae hrpZ gene was identified in Pseudomonas syringae pv. aptata NCPPB 2664, the causal agent of bacterial blight in sugar beet, lettuce and other plants, and in E. coli DH10B (pCCP1069) containing the P. syringae pv. aptata hrp gene cluster. PCR with oligonucleotides, based on the hrpZ_Pss gene and used as primers with the total genomic DNA of P. syringae pv. aptata, amplified a 1 kb fragment that hybridized with the probe in highly stringent conditions. The amplicon was cloned into the pGEM-T® plasmid vector, amplified in E. coli DH5 and sequenced. The sequence showed 95%, 83% and 61% identity with those of hrpZ_Pss, hrpZ_Psg and hrpZ_Pst genes encoding the harpins of the P. syringae pv. syringae, glycinea and tomato, respectively. The amplicon was cloned into the pMAL® expression system. The expressed protein, fused with maltose-binding protein, was cleaved with a specific protease factor Xa, and purified using affinity chromatography. On the basis of the amino acid sequence and its ability to induce HR in tobacco leaves, it was identified as a P. syringae pv. aptata harpin.     

Evaluation of fatty acid methyl ester profile and amplified fragment length polymorphism analyses to distinguish five species of Phytophthora associated with ornamental plants

Fatty acid methyl ester (FAME) profiles and amplified fragment length polymorphisms (AFLPs) were evaluated as tools for identifying species of Phytophthora. Five isolates of each of Phytophthora cactorum, Phytophthora citrophthora, Phytophthora cinnamomi, Phytophthora nicotianae and Phytophthora cryptogea were subjected to both analyses to examine variation among and within species. In FAME analysis, isolates of P. cactorum, P. cinnamomi and P.nicotianae were clustered by species, but isolates of P. citrophthora and P.cryptogea were divided into multiple clusters based on greater variations within these two species. The AFLP analysis differentiated all five species of Phytophthora. The five isolates of each species were grouped in a separate terminal cluster, but diversity within a species cluster varied considerably with variation greater in P. cryptogea and P. citrophthora. Comparing the dendrograms based on FAME and AFLP analyses, the overall patterns of both were similar. The P. cactorum cluster was distinct from clusters of the other four species, which formed one large cluster. The higher values of percentages of polymorphic loci and gene diversity in AFLP analysis substantiated diversity observed among isolates of P. citrophthora and P. cryptogea in FAME and AFLP dendrograms. Both FAME and AFLP appear to be useful tools for identifying species of Phytophthora, but only AFLP analysis has potential to study genetic and phylogenetic relationships within and among species in this genus.     

Effects of R-(1-amino-2-phenylethyl)phosphonic acid on glyceollin accumulation and expression of resistance to Phytophthora megasperma f.sp. glycinea in soybean

(R)-(1-Amino-2-phenylethyl)phosphonic acid (R-APEP), an inhibitor of phenylalanine ammonia-lyase (PAL), was applied to the tap root of 42-h-old soybean (Glycine max. (L.) Merrill cv. Harosoy 63) seedlings during inoculation with zoospores of the incompatible race 1 of Phytophthora megasperma f.sp. glycinea (Pmg1) for 2 h and during a subsequent incubation period. In contrast to L-2-aminooxy-3-phenylpropionic acid, R-APEP was not toxic to the zoospores which remained virulent in presence of the inhibitor. A 50% inhibition of PAL activity in vitro was observed with 4.2 M R-APEP and with 36 M of the S-enantiomer. When R-APEP at 330 M was applied for a total of 36 h to the seedlings, resistance against Pmg 1 was abolished. Such seedlings were indistinguishable in appearance from those seedlings which had been inoculated with the compatible race 3 of Pmg. Roots treated with R-APEP at 330 M showed a reduction of about 47% in glyceollin content when measured 12 h after inoculation, and with 1 mM a 67% reduction. In contrast, treatment with S-APEP (1 mM) caused only a 20% reduction in glyceollin content. As determined by indirect immunofluorescence of fungal hyphae in cryotome cross-sections of roots, the growth pattern of the incompatible race 1 of Pmg changed to that of the compatible race 3 under conditions where R-APEP caused loss of resistance against Pmg 1. The results support the concept of an important role of glyceollin in resistance of soybean against incompatible races of the fungus.Abbreviations R-APEP, S-APEP R.S enantiomers of (1-amino-2-phenylethyl)phosphonic acid - L-AOPP L-2-aminooxy-3-phenylpropionic acid - PAL phenylalanine ammonia-lyase (EC 4.3.1.5) - Pmg 1 Phytophthora megasperma f.sp. glycinea race 1 - Pmg 3 Phytophthora megasperma f.sp. glycinea race 3     

In vitro inhibition of Candida albicans growth by plant extracts and essential oils

The opportunistic Candida albicans yeast strain ATCC 10261 grows at 37 °C and gives germ tubes after 3 h on corn meal agar and blood plasma. It produces chlamydospores and assimilates sucrose, dextrose, galactose, maltose, trehalose and xylose among the tested carbon sources. Other growth characters were also investigated. The agar diffusion cut plug technique revealed that 200 l of Foeniculum vulgare Miller (fennel), Mentha piperita L. (peppermint) and Citrus limon (lemon) essential oils showed inhibitory actions. Fumigation test of the three essential oils had complete inhibition on the growth. The essential oil of Eucalyptus occidentalis End1 (eucalyptus, eucalypt) had no influence on C. albicans growth by the two tests. Meanwhile, methanol extracts of both leaves and male cones of the conifer Thuja orientalis (eastern thuya) had an inhibitory influence on the growth by two tests (cut plug and filter paper disc assay). In comparative tests the antibiotics mycostatin and dermatin had an inhibitory activity on C. albicans at the concentrations of 50–80 g per hole. Crude methanol extract of leaves of eastern thuya (10–80 g/ml) reduced C. albicans growth and intercellular protein nitrogen on liquid media.     

Nutrient study for the transition from earthen sedimentation ponds to ones lined with pvc in integrated mariculture systems, what needs to be done?

Stable diatom populations in earthen ponds for fishpond effluent treatment supported fast rates of bivalve growth in integrated mariculture systems. However, when these ponds were lined with PVC plastic sheets to prevent seepage, the populations of benthic diatoms dwindled, and did not support, as before, a commercially acceptable rate of growth by oysters and clams. Experiments were undertaken to understand the problem and restore the diatom productivity of such ponds. Clones of Amphora luciae, A,cftenerrima, Cylindrotheca closterium, Navicula cf lineola, N.cf lenzii, N. salinicola, N. cf viminoides, and Nitzschia laevis were isolated in axenic culture from an earthen sedimentation pond. Their N, P, Si, and trace element requirements for growth in fully defined media, and in media formulated with mariculture effluent, were studied in axenic batch culture. In fully defined batch culture tests, most of the isolates achieved their highest density in media with 32 M P, 0.7 mM N, 20 M Fe, 10 nM–20 M Mn, 10–20 M Zn and Co, and 17.5 M Si. Enrichment by trace elements and Si stimulated the populations of these diatoms even in media based on nutrient-enriched mariculture effluents. However, in large flow-through agnotobiotic mesocosms (700 L), only Si enrichment was needed. Si concentration >100 M was required to promote the sustained blooms of diatoms in full-sized and commercial PVC-lined fishpond effluent treatment ponds (300 m², 1 m depth). Except for Si, the requirements of the diatoms for micronutrients were apparently fully satisfied by the fishpond effluents (uneaten food and fish-waste). A molar ratio of 1:1 between Si and N is necessary to sustained dense diatom populations in the pond water. It is therefore recommended to enrich plastic lined mariculture effluent treatment/sedimentation ponds with Si, if the goal is to raise bivalves as a secondary crop.     

The relationship between cell size and viability of soil bacteria

The number of bacterial cells in soil that form colonies on nutrient agar represent a small fraction of the direct microscopic counts (DMC). The colony-forming cells have larger cell dimensions than the very small (dwarf) cells which represent the majority of the DMC. This may indicate that the dwarf cells are species unable to form visible colonies on agar, or that they swell to normal dimensions when growing. Indigenous bacterial cells were separated from soil by density gradient centrifugation and fractionated according to diameter by filtration through polycarbonate filters. Each filtrate was studied with respect to DMC, cell dimensions, colony-forming cells (visible colonies and microcolonies), and cell dimensions during growth on the agar. The calculated average percent viability was only 0.2% for cells with diameters below 0.4m, about 10% for cells with diameters between 0.4 and 0.6m, and 30–40% for cells with diameters above 0.6m. Only 10–20% of the viable cells with diameters <0.4m increased their diameter to >0.4m prior to growth. Thus, size change during starvation and growth cycles did not explain the high numbers of dwarf cells observed by microscopy. The results show that despite the relatively low number of colony-forming bacteria in soil, the species that form colonies may be fairly representative for the medium size and large cells, which constitute a major part of the bacterial biovolume. Thus plate counting could be a useful method to count and isolate the bacteria accounting for much of the biovolume in soil. The origin of the dwarf cells is still unclear, but the low number of small cells that increased in size seems to indicate that the majority of these bacterial cells are not small forms of ordinary sized bacteria.     

Antagonism between entomopathogenic fungi and bacterial symbionts of entomopathogenic nematodes

Mutual effects between the symbiotic bacteria of entomopathogenic nematodes, Photorhabdus luminescens and Xenorhabdus poinarii, and entomopathogenic fungi were investigated in vitro. A dual culture assay on nutrient agar supplemented with bromothymol blue and triphenyltetrazolium chloride (NBTA) medium revealed that P. luminescens is antagonistic to Metarhizium anisopliae, Beauveria bassiana, B. brongniartii and Paecilomyces fumosoroseus by inhibiting their growth and conidial production; the fungal growth was not inhibited by X. poinarii. In a second laboratory experiment, crude extract produced by M. anisopliae was tested for its activity against P. luminescens and X. poinarii. Crude extract from M. anisopliae was antibacterial to P. luminescens and X. poinarii at 1000 g/ml and inhibited their growth on NBTA, but had no effect at 100 or 10 g/ml. The influence of the crude extract of M. anisopliae on the dispersal of infective juveniles (IJs) of Heterorhabditis megidis and Steinernema glaseri was assayed on Sabouraud Dextrose Agar (SDA) plates. Results showed that the crude extract of M. anisopliae had no toxic effects even at highest concentration (1000 g/ml).     

Changes in phosphorus concentrations and pH in the rhizosphere of some agroforestry and crop species

The aim of this work was to assess whether agroforestry species have the ability to acquire P from pools unavailable to maize. Tithonia diversifolia(Hemsley) A. Gray, Tephrosia vogelii Hook f., Zea mays and Lupinus albusL. were grown in rhizopots and pH change and depletion of inorganic and organic P pools measured in the rhizosphere. Plants were harvested at the same growth stage, after 56 days for maize and white lupin and 70 days for tithonia and tephrosia, and the rhizosphere sampled. The rhizosphere was acidified by tithonia (pH change –0.3 units to pH 4.8) and lupins (–0.2 units to 4.9), alkalinised by tephrosia (+0.4 units to pH 5.4), and remained unchanged with maize growth. Concurrent with acidification in the rhizosphere of tithonia there was a decline in resin-P (0.8 g P g^–1). However, there was also a decline in NaOH extractable inorganic P (NaOH-P_i) (5.6 g P g^–1 at the root surface) and organic P pools (NaOH-P_o) (15.4 g P g^–1 at 1.5 mm from the root), which would not be expected without specific P acquisition mechanisms. Alkalinisation of tephrosia rhizosphere was accompanied by changes in all measured pools, although the large depletion of organic P (21.6 g P g^–1 at 5 mm from the root) suggests that mineralisation, as well as desorption of organic P, was stimulated. The size of changes of both pH and P pools varied with distance away from the rhizoplane. Decline of more recalcitrant P pools with the growth of the agroforestry species contrasted with the effect of maize growth, which was negligible on resin-P and NaOH-P_i, but led to an accumulation of P as NaOH-P_o (14.2 g P g^–1 at 5 mm from the root). Overall the depletion of recalcitrant P pools, particularly P_o, suggests that the growth of tithonia and tephrosia enhance desorption and dissolution of P, while also enhancing organic P mineralisation. Both species appear to have potential for agroforestry technologies designed to enhance the availability of P to crops, at least in the short term.     

Phytophthora Species Infecting Hardy Ornamentals in Nurseries and the Managed Environment in Scotland

Between 2002 and the end of 2009, more than 4000 samples from hardy ornamental plants, collected in surveys for Phytophthora ramorum, were examined to establish the occurrence and diversity of Phytophthora species in Scotland. The samples were gathered from more than 77 plant genera in nurseries, gardens and amenity landscapes. Fifteen different Phytophthora spp. were isolated and identified either by polymerase chain reaction (PCR) or by sequencing of the ITS1, 5.8S subunit and ITS2 region of the ribosomal RNA gene. The most widespread Phytophthora spp. were P. ramorum and P. syringae, followed by P. cactorum, P. kernoviae, P. plurivora, P. cambivora, P. citrophthora, P. taxon ‘Pgchlamydo’, P. pseudosyringae and some single isolates of P. cinnamomi, P. cryptogea, P. gonapodyides, P. nicotianae and P. hibernalis. One isolate did not match any known species. In relation to the number of samples, Phytophthora was found more frequently in trade premises than in gardens or amenity landscapes and the species diversity was higher, highlighting the risks involved in plant trade.