Pythium SPP in roots of wheat and rye-grass in Western Australia and their effect on root rot caused by Gaeumannomyces graminis var. tritici

Pythium acanthophoron, P. echinulatum, P. irregulare, P. vanterpoolii, P. vexans, P. violae and a Pythium sp. (unidentified) were isolated from wheat and rye-grass roots. Pythium spp were isolated at a higher frequency at seedling and tillering stages than at other stages of sampling. A greater proportion of these were obtained on potato dextrose agar than on the same medium with lactic acid or streptomycin.

P. irregulare, P. violae and P. vanterpoolii were pathogenic to wheat and rye-grass in sterilized and non-sterilized soil, and with the exception of P. vanterpoolii on rye-grass, reduced their fresh shoot and root weights. P. acanthophoron, P. echinulatum, P. vexans and the Pythium sp. were non-pathogenic to wheat and rye-grass. P. vexans and Pythium sp., however, increased the fresh shoot and root weights of wheat and rye-grass in sterilized and non-sterilized soil.

P. irregulare, P. violae and P. vanterpoolii increased the percentage mortality of wheat and rye-grass resulting from infection by Gaeumannomyces graminis var. tritici in sterilized and non-sterilized soil, with the exception of P. vanterpoolii on rye-grass. P. vexans, the Pythium sp. and P. echinulatum reduced the percentage mortality of wheat and rye-grass resulting from take-all in both soil treatments.     

Saprophytic survival of the take-all fungus and its antagonist, Gaeumannomyces graminis var. graminis under conventional and no-tillage

The saprophytic survival of the take-all fungus, Gaeumannomyces graminis var. tritici, and its antagonist, G. graminis var. graminis, was studied over 9-month periods in 1982 and 1983 under conventional and no-tillage cultivation. In 1982, when the rainfall for the 9-month period was 30.4% below the long-term average, the survival of the fungi was comparable under the two tillage systems. However, the survival of G. graminis var. graminis was significantly greater (P 0.05) than that of G. graminis var. tritici at each sampling time. In 1983, when the rainfall for the 9-month period was 25.1% above the long-term average, the survival of both fungi was significantly greater under no-tillage than under conventional tillage. The survival of the two isolates of G. graminis var. graminis after 3 months was significantly greater (P 0.05) than that of the two isolates of the pathogen. The implications for the greater survival of the fungal antagonist compared to the take-all fungus under no-tillage are discussed in relation to the biological control of take-all.     

Comparative FT-Raman spectroscopy of Xanthoria lichen-substratum systems from temperate and antarctic habitats

Lichens have a primary role in the biodeterioration of rock substrata and in soil formation. In extreme Antarctic rock-face habitats, their exposed epilithic growth form makes them vulnerable to environmental stress, especially to increased UVB radiation within the late winter ozone “hole”. In this study, FT-Raman spectra of intact epilithic samples of the highly-pigmented lichen species Xanthoria elegans and Xanthoria mawsonii from a continental Antarctic habitat in central Victoria Land and Xanthoria parietina from a maritime temperate location in Scotland have been compared. Vibrational assignments have been made for their pigments, based on parietin and an anthraquinone model. Other significant spectral features are assigned to biodegradative secondary metabolites, cellulose and incorporated substratal rock particles. Differential distribution of parietin pigment bands in the profile of an X. elegans thallus is probably related to the high intensity of UV-radiation reaching its Antarctic cold desert surface environment. The significant differences in Raman spectra between epiphytic X. mawsonii and epilithic X. elegans at the same site possibly indicate different biochemical UV survival strategies. In contrast to spectra from other lichen species studied in our laboratories, the Xanthoria encrustations contain very little calcium oxalate, formed by reaction of oxalic acid with calcareous substrata. The 462 cm⁻¹ ν(SiO) band of quartz is found in the Raman spectra from both upper and lower surfaces of the lichen encrustations, confirms the physical incorporation of the substratum into the thallus.     

Responses of root-feeding nematodes (Helicotylenchus spp.) to local and non-local populations of the host plant Ammophila arenaria

The root-feeding nematode community of wild plants may vary throughout their natural range. Little is known about how the variation of wild plants along their range affects their relationship with root-feeding nematodes. In the present study, we examined local and non-local combinations of host plants and root-feeding nematodes to test the hypothesis that nematode reproduction is favoured by local hosts. In two indoor experiments, we exposed populations of the wild dune grass Ammophila arenaria from northern and southern European coastal sand dunes to plant parasitic nematode species (Helicotylenchus spp.) from those same geographical origins. First, we used the southern nematode species to determine whether the effect of a local versus a non-local host may depend on nematode density. Then, in a cross-inoculation experiment we investigated how both nematode species performed with their local, as compared to the non-local hosts.

In both experiments, plant biomass and ontogenetic characteristics were not significantly different between the northern and southern populations. The applied nematode densities did not have a negative impact on plant performance. This allowed us to consider the response of the two different nematode species and their host plants without co-varying differences in plant responses. Reproduction of the nematode species differed according to host origin, but contrary to what we expected, nematode species did not perform better on their local hosts. Helicotylenchus n. sp., the southern species originating from Portugal, performed better on the non-local than on the local host. Male to female ratios were significantly different between the two nematode populations and were lowest in Helicotylenchus pseudorobustus from The Netherlands. Female and juveniles percentages were also quite distinct, with more females in the nematode species from The Netherlands and more juveniles in the nematode species from Portugal.

We concluded that ectoparasitic root-feeding nematodes Helicotylenchus spp. do not necessarily perform best on their local host population of the foredune grass A. arenaria. Our results imply that the natural distribution of Helicotylenchus spp. along the European coast is determined by other factors than host populations. These other factors that could be abiotic, e.g. water availability, or biotic, e.g. local natural enemies adapted to Helicotylenchus spp. Introducing plant genotypes from other parts of the natural range will, therefore, not necessarily lead to reduced abundance of semi-endo or ectoparasitic root-feeding nematodes.     

裸脚菇0612-9提取物对柑橘青、绿霉的抑菌活性及作用机制

为探索裸脚菇0612-9提取物(GSFE)对意大利青霉(Penicillium italicum)和指状青霉(P. digitatum)的抑菌活性和作用机理,本试验采用菌丝生长速率法测定GSFE对意大利青霉和指状青霉的抑菌活性,分析GSFE处理后意大利青霉和指状青霉的菌丝形态、细胞膜通透性和麦角固醇含量变化情况,并通过靶位竞争剂试验探究GSFE的抑菌机理。结果表明,GSFE对意大利青霉和指状青霉的半有效浓度(EC₅₀)值分别为116.76和147.74 μg·mL^-1,最小抑菌浓度(MIC)均为200 μg·mL^-1;经质量浓度为EC₅₀和MIC的GSFE处理后意大利青霉和指状青霉菌丝体均发生严重的皱缩、干瘪,并且胞内呈空泡状结构,细胞质大量减少,胞外相对电导率显著上升,菌体内核酸、可溶性蛋白等胞内物质含量显著降低。这表明意大利青霉和指状青霉细胞膜通透性增加,胞内物质外泄,细胞膜完整性遭到破坏。经浓度为EC₅₀的GSFE处理的意大利青霉和指状青霉菌丝体,其麦角固醇含量均显著降低,分别仅为对照组的17.92%和20.13%。由此可见,GSFE主要通过抑制意大利青霉和指状青霉菌丝体的麦角固醇合成而损伤病原真菌细胞膜的结构和功能。本研究结果为后续开发新型微生物源柑橘采后保鲜剂提供了设计思路。     

Influence of soil and host plant crop on the genetic diversity of Azospirillum amazonense isolates

The genetic structure of Azospirillum amazonense populations isolated from the rhizosphere soil and washed and surface-sterilised roots of rice, maize and sorghum plants, cropped simultaneously in two different soils (clay loam and sandy loam) was characterised. Genetic diversity was measured by restriction fragment length polymorphism of the amplified 16S–23S rDNA intergenic spacer region (RISA-RFLP) and cluster analysis. Four genetically distinct clusters of isolates were observed with 78% similarity, suggesting that the A. amazonense population was heterogeneous at the strain level regardless of the soil type or host plant. Analysis of molecular variance (AMOVA) demonstrated that the host plant had a highly significant selective effect on the genetic structure of this species, especially on those isolates intimately associated with them, but also to a lesser extent on isolates from the rhizosphere and washed roots. The soil type also had a highly significant selective effect on A. amazonense genetic diversity, especially for those isolates from the rhizosphere soil. The selective effect of the soil type combined with that of the host plant suggests that environmental factors, such as soil texture and composition of exudates provided by C₃ or C₄ plants, play major roles in the overall genetic structure of A. amazonense populations associated with these cereals.     

Biological control of Phytophthora parasitica var. Nicotianae on tobacco seedlings with non-pathogenic binucleate Rhizoctonia fungi

Nonpathogenic binucleate Rhizoctonia fungi (BNR) controlled black shank caused by Phytophthora parasitica var. nicotianae on greenhouse-grown tobacco seedlings in styrofoam float trays. Three BNR isolates were incorporated into a soil-less mix on colonized, pulverized, sifted rice particles; colonized whole rice grains; or on pelleted tobacco seeds coated with 0.5% methyl cellulose. Five-wk-old seedlings were inoculated with zoospores of P. parasitica var. nicotianae and disease rated over 10 d. The level of protection varied with method of BNR application, ranging from 40 to 70%. Overall, control was better when BNR isolates were applied on rice inocula rather than on BNR-colonized tobacco seeds. From 15% to 80% of individual roots from seedlings grown in soil-less mix amended with BNR-colonized rice grains were colonized while only 0–20% of roots from seedlings grown from BNR-colonized tobacco seeds were colonized. Likewise, 37–100% of soil-less mix amended with BNR-colonized rice grains contained BNR's while less than 3% of soil-less mix was colonized when seedlings emerged from BNR-colonized tobacco seeds. This is the first demonstration of biocontrol of Phytophthora by BNR fungi.     

Mortality trends in the African cherry (Prunus africana) and the implications for colobus monkeys (Colobus guereza) in Kakamega Forest, Kenya

Prunus africana (Hook.f.) Kalkm. is a secondary forest canopy tree species that has been declining over much of its geographical range in sub-Saharan Africa during recent decades due to unsustainable harvesting of its bark for the international medicinal plant trade. One of the locations where the species is experiencing rapid mortality is Isecheno study site in the Kakamega Forest, Kenya where this study was conducted. Between 1997 and 2003, 21% of the P. africana (10 cm DBH) at Isecheno died and an additional 9% experienced 50% canopy dieback. However, scars from bark harvesting on P. africana were relatively small and scarred trees were not more likely to be dead or dying than unscarred trees, suggesting that bark exploitation is not causing P. africana mortality at Isecheno. Other possible causes that require further evaluation include disease, insect attack, nutrient deficiency, and/or climatic fluctuation. The poor regeneration of P. africana at Isecheno can likely be explained by the relative lack of recent disturbance coupled with the thick undergrowth layer at this site. P. africana mortality is of concern not only because the species is listed as Vulnerable by IUCN, but also because black and white colobus monkeys [Colobus guereza (Rüppell, 1835)] at Isecheno exploit it as their top food species and are particularly reliant on its leaves during times of ‘preferred' Moraceae fruit scarcity. The anticipated continued decline of P. africana may have adverse effects on C. guereza feeding habits, intergroup relations, and population density at Isecheno. Conservation of P. africana offers a formidable challenge since the species appears to require disturbance for regeneration, yet at sites where disturbance is occurring, P. africana is often a target of bark harvesters engaging in unsustainable levels of exploitation.     

不同氮素形态配比对三七根腐病的影响

为明确氮素形态及其配比对三七根腐病发生的影响,采用盆栽试验,研究了5种不同氮素形态配比(铵硝配比分别为0∶100、25∶75、50∶50、75∶25和100∶0)及尖孢镰刀菌(Fusarium oxysporum)侵染对三七[Panax notoginseng (Burk.) F. H. Chen]生长、有效成分以及抗性指标的影响。结果表明,不同氮素形态配比对三七生物量和皂苷含量无明显影响,铵态氮(${NH_{4}}^{+}-N$)可促进可溶性糖的累积;病原菌侵染使三七叶绿素、可溶性糖和黄酮含量降低,随着${NH_{4}}^{+}-N$比例的增加,病情指数增加,过氧化物酶(POD)、多酚氧化酶(PPO)和苯丙氨酸解氨酶(PAL)活性升高,同时伴随酚类和木质素的累积。综上所述,低铵硝配比(特别是25∶75)有利于三七的生长,可降低三七病情指数,减轻三七根腐病的发生。本研究从氮肥施用层面为三七根腐病的防控提供了理论依据。     

β-谷甾醇在辣椒疫霉菌生长发育中的作用研究

辣椒疫霉菌是一种缺乏甾醇合成必要基因的疫霉属重要植物病原卵菌,其可利用植物中富含的β-谷甾醇等甾醇类物质完成生活史。为了明确β-谷甾醇在辣椒疫霉菌不同生长发育阶段中的作用,本研究设置系列浓度梯度(0.2、1.0、5.0、25.0、125.0μg·mL^-1),测定了其对辣椒疫霉菌孢子囊和卵孢子形成的影响,观测了β-谷甾醇处理后菌丝的生长及形态结构,探究了其对辣椒疫霉菌细胞膜透性的影响。结果表明,β-谷甾醇对辣椒疫霉菌生长发育具有重要作用,表现为低浓度促进生长发育,高浓度抑制生长发育。具体表现为：当β-谷甾醇浓度为0.2μg·mL^-1时,其对辣椒疫霉菌菌丝生长、孢子囊和卵孢子形成具有促进作用;当β-谷甾醇浓度高于5.0μg·mL^-1时,其对菌丝生长及孢子囊和卵孢子形成表现出抑制作用;且随着β-谷甾醇浓度的升高,其抑制作用随之增强。在β-谷甾醇对辣椒疫霉菌菌丝生长抑制有效中浓度(EC₅₀=10.0μg·mL^-1)下,其对菌丝有明显的致畸作用,细胞膜通透性增大,对菌丝生长、孢子囊和卵孢...     

Selective consumption and digestion of litter microbes by Porcellio scaber (Isopoda: Oniscidea)

In feeding preference tests with artificial diets consisting of food sources inoculated with different types of litter microbes, Porcellio scaber was capable of discriminating between different microbe species. Generally, microbial colonisation increased the attractiveness of a given food source, in particular, when the food source was of low quality (cellulose) and when food sources were inoculated with single species of actinomycetes (Streptomyces celluloflavus or Pseudonocardia autotrophica). In most cases, actinomycetes (Gram-positive bacteria) were preferred over both Gram-negative bacteria and fungi, whether or not these microbes exhibited cellulolytic activity. Enzymatic in vitro digestion of both the Gram-positive S. celluloflavus and P. autotrophica was significantly greater than that of Gram-negative bacteria (Pseudomonas fluorescens and Myxococcus xanthus) or fungi (Chaetomium globosum and Fusarium ventricosum). S. celluloflavus biomass was more effectively incorporated into isopod biomass than that of fungi and Gram-negative bacteria; P. autotrophica was more effectively incorporated into isopod biomass than that of Gram-negative bacteria. Based on these results, we hypothesise that P. scaber preferentially feeds on those microbes that it can readily digest. Whether this holds true for other Gram-positive bacteria or for other detritivores awaits investigation.     

复配杀菌剂防治平菇尖孢镰刀菌病害的效果测定

为筛选应用于平菇栽培的高效低残留杀菌剂,本试验研究了复配杀菌剂(使百功+多菌灵、使百功+克霉灵、多菌灵+克霉灵)对尖孢镰刀菌与平菇菌丝生长的影响及其在平菇栽培中的应用效果。结果表明,3种复配杀菌剂抑制尖孢镰刀菌菌丝生长的EC₅₀值分别为3.67、4.51和7.01 mg·L^-1,均显著小于对应的单药杀菌剂;3种复配杀菌剂抑制平菇菌丝生长的EC₅₀值分别为156.41、121.97和237.38 mg·L^-1,是其抑制尖孢镰刀菌菌丝生长EC₅₀值的27~43倍。在平菇栽培发酵料中使用0.1%~0.3%的复配杀菌剂使百功+克霉灵,菌丝生长速度加快,生物学效率升高;与未添加杀菌剂处理相比,污染率降低6.1~8.8个百分点;与使百功处理相比,平菇子实体中的农药残留量降低71.8%~76.6%。综上,复配杀菌剂能有效降低平菇子实体中的农药残留,其中使百功+克霉灵复配杀菌剂效果最好,是一种高效低残留的平菇枯萎病防治药剂。     

Tetracycline-Resistant Escherichia coli in a Small Stream Receiving Fish Hatchery Effluent

We examined the impact of the effluent discharged from a freshwater (trout and related species) fish hatchery on the presence of antibiotic-resistant microorganisms in a small stream. There had been no documented use of antibiotics in the hatchery for at least 6 months prior to our study, although a variety of biocides were employed routinely for cleaning. Heterotrophic bacteria and Escherichia coli were isolated from both water column and sediment samples at sites above and below the discharge of the hatchery effluent as well as from the hatchery effluent itself. Randomly chosen isolates (≥96 isolates per site) were tested for their resistance to ampicillin, cephalexin, erythromycin, and tetracycline. Resistance to at least one antibiotic was found in greater than 30% of both the heterotrophic isolates and the E. coli isolates from each of the sites. There were no significant differences among the sites in the proportion of the heterotrophic isolates resistant to any specific antibiotic. The proportion of E. coli isolates resistant to tetracycline in the hatchery effluent and in both the downstream water and sediment samples was significantly higher than in either the upstream water or sediment. These results support the possibility of the hatchery as a source of tetracycline-resistant microorganisms even in the absence of recent use of this antibiotic.     

Soil fungal population in preharvest maize ecosystem in different tillage practices in Argentina

The distribution of the soil borne fungal population in maize non-rhizospheric soil in experimental trials were studied during the harvest seasons 2000/2001 and 2001/2002. The effect of different tillage practices was evaluated. Soil samples were collected from three tillage treatments, conventional tillage, reduced tillage and no tillage, with and without grazing. The distribution of fungal propagules in different treatments was compared. Soil samples were collected from the top soil (3 cm) before planting, in the sprong. No tillage without grazing and reduced tillage with grazing had the highest densities of filamentous fungi (5.71 and 5.85 log, respectively). The mycological survey showed the presence of six genera of filamentous fungi. They were Aspergillus, Fusarium, Penicillium, Trichoderma, Cladosporium, Alternaria. The species identified from genus Aspergillus were A. flavus, A. restrictus, A. candidus, A. parasiticus and other Aspergillus spp. The species identified from genus Penicillium were P. pinophylum, P. citreonigrum, P. implicatum, P. purpurogenum, P. minioluteum, P. waksmanii, P. restrictum, P. rugulosum, P. funiculosum and P. variabile. Species from genus Fusarium were identified as F. verticillioides, F. oxysporum, F. proliferatum and others Fusarium species. The isolation frequency of Aspergillus increased in the no tillage and grazing practices treatments. The data indicate that different agricultural practices impact soil inocula of principal maize toxigenic fungi in the production area. To our knowledge, this is the first report on the effect of tillage management practices on fungal populations in preharvest maize agroecosystem in Argentina.     

Evidence for multiple origins of Wolbachia infection in springtails

Bacteria of the genus Wolbachia (Rickettsiae) are endosymbionts found in many species of invertebrates. The traditional division of Wolbachia lines into four supergroups has recently been challenged with the finding of a fifth supergroup. Until now, this E supergroup exists of a single host species of the order Collembola (springtails) and is hypothesized to form a ‘missing link’ between Wolbachia lines in higher arthropods and nematodes. We have sequenced the 16S rDNA, the ftsZ and the wsp genes of a Wolbachia lineage present in the sexually reproducing collembolan Orchesella cincta. We tested the hypothesis on the origin of Wolbachia in Collembola by adding this new Wolbachia lineage and a lineage found in the collembolan Mesophorura macrochaeta to the Wolbachia phylogenetic tree. The addition of these two species clearly shows that Wolbachia is not monophyletic in Collembola. We conclude that the origin of Wolbachia in Collembola is a combination of vertical and horizontal transfer between coexisting species.     

利用12C6+重离子辐射和尖孢镰刀菌毒素筛选杂交兰抗茎腐病突变体

为创建抗茎腐病杂交兰资源,本研究以玉女兰类原球茎为材料,采用¹²C⁶⁺重离子辐射技术结合尖孢镰刀菌(Fusarium oxysporum)粗毒素筛选抗茎腐病突变体。结果表明,经不同剂量¹²C⁶⁺重离子辐射后,玉女兰类原球茎的死亡率差异显著,辐射剂量为50 Gy时,死亡率为54.66%;尖孢镰刀菌粗毒素对玉女兰类原球茎存活率影响显著,当粗毒素滤液浓度为80%时,玉女兰类原球茎存活率为41.98%。采用逐步筛选法对经50 Gy¹²C⁶⁺辐射后的玉女兰类原球茎进行抗茎腐病筛选,获得14个抗性系类原球茎,筛选率为4.67%;对抗性系类原球茎进行分化、生根壮苗和移栽,获得3个抗性系Z50Gt₁、Z50Gt₂和Z50Gt₃。在含80%粗毒素滤液的培养基上抗性系类原球茎的超氧化物歧化酶(SOD)和过氧化物酶(POD)的活性均高于对照,POD活性峰值比对照提高了867.67 U·g^-1·h^-1;丙二醛(MDA)含量呈现先高于对照,随着毒素胁迫时间的延长,转变为低于对照的趋势。对3个抗性系试管苗和小苗进行人工接种鉴定,结果表明,抗性系Z50Gt₂和Z50Gt₃的再生植株具有稳定的茎腐病抗性,2个抗病株系7个月大的盆栽植株病情指数分别为20.00%和19.33%,均为抗性级别。本研究结果为采用重离子辐射技术选育抗茎腐病杂交兰新品种奠定了基础。     

The Dalmatian pelican, Pelecanus crispus Bruch 1832, a recently world-endangered bird species

The world population of Dalmatian pelicans Pelicanus crispus, the largest pelican species of the genus Pelicanus, has decreased drastically since the last century. Its breeding range has diminished in relationship to agricultural and industrial development and draining of wetlands, and is now limited to the eastern part of the Old World. The present status of P. crispus is reviewed, and the number of breeding pairs in the world is estimated to be between 700–1100 in 16–24 different breeding sites. Migration and wintering are poorly known. Data on the food (strictly fish), the impact of P. crispus on fisheries and a peculiar feeding behaviour of Dalmatian pelicans is distinct association with the great cormorant Phalacrocorax carbo are discussed. New contributions on reproduction and predation are presented, and suggestions are made for conservation, monitoring and management.     

Evaluation of genetic diversity and plant growth promoting activities of nitrogen-fixing bacilli isolated from rice fields in South Brazil

Several strains of bacilli, mainly species of the genera Bacillus and Paenibacillus, displaying important plant growth promoting (PGP) characteristics were isolated from seven distinct rice production zones of the Rio Grande do Sul State, Brazil. Of 296 isolates, 155 were from rhizospheric soil and 141 from bulk soil. In order to evaluate the diversity among the isolates of each bacterial population the Shannon index was used on a 70% similarity basis. Diversity indices varying from 2.27 to 5.51 were obtained. Using principal coordinate analysis (PCA) to correlate bacterial diversity with soil parameters, it was found that soil pH was the characteristic most closely related to bacilli diversity. The bacilli isolated were also analyzed for some PGP activities. Of those 296 isolates, 94 and 148 produced between 0.1 and 30 μg of indole-3-acetic acid (IAA) ml⁻¹ in vitro after 72 and 144 h of incubation, respectively. Twenty-two isolates were able to solubilize phosphate and 32 isolates produced siderophores. Paenibacillus and Bacillus genera were the most prominent groups in the rhizosphere and soil populations analyzed. Paenibacillus borealis was the most frequent species in both locations. The isolate SVPR30, identified by 16S rRNA gene sequence analysis as a strain of Bacillus sp., was chosen for in vivo greenhouse experiments and proved to be very efficient in promoting a significant increase in the roots and shoot parts of rice plants. The identification and isolation of PGP bacilli from temperate and subtropical soils, which combine the ability to fix nitrogen with the production of substances capable to promote the plant growth, could significantly increase productivity of grain crops in Brazil.     

Response to root-knot nematodes of a germplasm collection of red clover and related species

A germplasm collection of red clover (Trifolium pratense L.) and seven related species was evaluated in greenhouse tests for resistance to Meloidogyne arenaria (Neal) Chitwood, M. hapla Chitwood, M. incognita (Kofoid & White) Chitwood, and M. Javanica (Treub) Chitwood. Plants were rated for root galling severity and nematode egg production at eight weeks after inoculation with 1500 nematode eggs. A resistance index, RI = (gall₂; + egg₂;), was generated to assess the plants' reaction to nematode infection as immune, highly resistant, resistant, moderately resistant, intermediate, moderately susceptible, susceptible, or highly susceptible. More than 98% of red clover accessions were intermediately to highly susceptible to all four root-knot nematode species. Only one accession, PI 271627 introduced from India, had a moderate resistance level to the four nematodes tested. About one third of the T. medium accessions were resistant or highly resistant to M. arenaria, M. incognita, and M. javanica whereas more than 50% of the T. alpestre accessions were highly resistant or immune to all four nematodes species. Genetic factors for resistance to root-knot nematode could be introduced into T. pratense through interspecific hybridization with T. medium and/or T. alpestre     

Effects of metals on the germination and growth of fungal isolates from New Caledonian ultramafic soils

Soils of New Caledonian mining areas have relatively high metal contents. Two ultramafic soils rich in extractable Mn, Fe, Ni and Co and two agricultural soils with much lower concentrations of metals were compared through different experiments. Microbial population numbers and their tolerance to Mn²⁺ and Ni²⁺ were estimated. The effect of five metals (Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺ and Mg²⁺) upon spore germination and mycelial growth was investigated for fungi isolated from the two types of soils. Nickel appeared to be the most toxic metal, but the other metals also had inhibitory effects at concentrations similar to those which occur in ultramafic soils. Spore germination was more sensitive to metals than mycelial growth. The toxic effects of the five metals were not cumulative when mixed together into the medium; antagonism between ions, partly neutralizing their effects may account for this. Fungal isolates from ultramafic soils appeared to be more tolerant to metals than those from agricultural soils. Some ultramafic soil isolates appeared to actually require the presence of metals, with their growth being stimulated by relatively high concentrations of these elements. Two fungal isolates of genera which are often common in agricultural soils (i.e. Curvularia and Fusarium), and which are not present in New Caledonian ultramafic soils were also tested. Curvularia was more sensitive to the five metals than all the other isolates and Fusarium was particularly inhibited by Ni²⁺. However, a proportion of the spores of each isolate was able to germinate and to grow moderately well in the presence of relatively high metal concentrations. Their absence from ultramafic soils is thought to result from their elimination by competitors that are more tolerant to metals.