Vermiculite Culture Research Articles

Evaluation Tolerant of Four Melon Genotypes in Early Growth Stage under Normal and Drought Stress Conditions

Plant breeding initiative in semi-arid and arid area are primarily focused on developing genotypes at early growth stage under normal conditions and keeping them steady during drought stress conditions. Therefore, four melon genotypes responses to drought stress were evaluated in this study during early growth stage. Two treatments for irrigation rates (Full Irrigation= 100%) and (Deficit Irrigation= 50%) were carried out in randomized complete block design (RCBD) with three biological replications in vermiculite culture in greenhouse in the research farm of faculty of agriculture at Sohag university in Egypt during season 2023. Young plants (45 days old plants) were utilized, and phenotypic traits 1º Leaf Score Tolerance, 2º Leaf Score Tolerance, Flowers Numbers, Vine Length, Green Leaves and Brown Leaves Numbers per vine were calculated by comparing differences in drought stress compared to control to identify tolerant and susceptible genotypes. The findings demonstrated that, in all estimated traits under drought stress conditions, there was significant variation between the studied four melon genotypes. whereas, the best results for all the studied traits were produced under normal conditions. Additionally, the highest significant positive correlation was found between 1º Leaf Score Tolerance and 2º Leaf Score Tolerance (0.966*) under normal conditions, and between Vine Length and Green Leaves Numbers per vine (0.999**) under drought stress conditions. Furthermore, the highest significant negative correlation was observed between 2º Leaf Score Tolerance and Flowers Numbers (-0.974*) and Flowers Numbers and Green Leaves Numbers per vine (-0.960*) under normal conditions, and between Vine Length and Brown Leaves Numbers per vine (-0.974*) and Green Leaves Numbers per vine and Brown Leaves Numbers per vine (-0.981*) under drought stress conditions. Besides, Euclidean heatmap clustering analysis grouped studied genotypes according to their response to normal and drought stress conditions, indicating that, the studied melon genotypes offer high potential for particular breeding purposes. These results have produced helpful framework for breeding strategies in the future under drought stress conditions. Conversely, detailed studies are crucial to predict drought stress tolerance performance in novel breeding strategies.

The Leafy-Stem-Buried Etiolation Contributed to the High Efficiency of Rootstock Vegetative Propagation in Avocado (Persea americana)

Because of their tolerance to root rot and many abiotic stresses, rootstocks are generally required for commercial avocado production. However, cutting and air-layering, which are popular methods of vegetative propagation for producing large numbers of uniform and genetically identical plants, have been unsuccessful for years. To develop a practical and efficient rooting procedure for selected avocado clonal rootstocks, the present research investigated the effects of various factors on rooting cutting. Shoots were divided into three groups (air layering, direct cutting, and stem-buried etiolation) and treated with different combinations (plant growth regulators, PGRs; soaking time; and culture media), in which orthogonal or randomized-block designs were used. The rooting rate, average root length, average root number, average root dry weight, and rooting quality (Q value) were used as evaluation indicators. The results show that etiolation treatment of the mother shoot is the requisite condition for avocado shoot rooting. In addition, the rooting effect of etiolated cuttings was strongly impacted by PGR type, concentration, and soaking time, whereas no significant differences were detected among the culture media. Among these factors, the roots and the survival rates of etiolated cuttings of two hard-to-root varieties were optimal under the following conditions: indolebutyric acid concentration of 2500 mg/L, dipping duration for 5 s, and perlite:vermiculite culture at 1:1. The rooting rate of ‘Dusa’ was generally greater than that of ‘Duke 7’ and reached 82%.

Effects of Burkholderia sp. Y4 on Cadmium Damage and Uptake in Rice Seedlings

In order to investigate the effects of Burkholderia sp. Y4 on rice seedlings under cadmium (Cd) stress, seed germination and vermiculite culture experiments were conducted using low Cd-accumulation xiangzaoxian 24 (X24) and high Cd-accumulation Tyou 705 (T705) varieties. The effects of Burkholderia sp. Y4 on rice growth, oxidative damage caused by Cd, and Cd accumulation were studied. Additionally, the Cd2+ flux rates in the elongation zone of rice roots under Burkholderia sp. Y4 application were detected using non-invasive micro-test technology. Burkholderia sp. Y4 alleviated the inhibition effect of Cd on rice seed germination by 13.8%. After inoculation with Burkholderia sp. Y4 for 7 d, the length of rice roots and buds increased by 83.3% and 12.2%, and their dry weight increased by 56.8% and 12.5%, respectively; those in the 10 d Y4 inoculation group increased by 28.6% and 20.0% in length and by 113.2% and 46.0% in dry weight, respectively. Burkholderia sp. Y4 inoculation also alleviated rice oxidative stress damage caused by Cd. The application of strain Y4 significantly reduced the content of the oxidative damage product malondialdehyde (MDA) in the shoots and roots of rice seedlings by 21.5% and 16.9%, respectively. Under Burkholderia sp. Y4 inoculation, the significant changes in antioxidant enzyme SOD and CAT activities caused by Cd stress disappeared in rice roots; those in shoots also decreased from 176.9% and 74.8% to 53.3% and 21.5%, respectively. Conversely, Burkholderia sp. Y4 inhibited Cd uptake by rice seedlings with different genotypes, including the low Cd-accumulation variety X24 and high Cd-accumulation variety T705. The root application of strain Y4 significantly reduced Cd accumulation in the shoots and roots of rice seedlings by 79.2% and 62.7% in T705 and by 57.3% and 24.1% in X24, respectively. The Cd2+ flux rate of high Cd-accumulation variety T705 was significantly higher than that of low Cd-accumulation variety X24. Under Burkholderia sp. Y4 inoculation, the yellow membrane was formed on the root surface of rice seedlings, and the Cd2+ flux rate in the elongation zone of T705 and X24 roots decreased by 36.0% and 35.0% in 3-day-old seedlings, as well as by 44.6% and 24.9% in 10-day-old seedlings, respectively. In conclusion, Burkholderia sp. Y4 inoculation inhibited the toxic effects of Cd on rice seedling growth through alleviating oxidative stress and damage caused by Cd. Furthermore, the root application of Burkholderia sp. Y4 effectively decreased the Cd2+ flux rate in the elongation zone of roots to inhibit the Cd uptake and accumulation in roots and shoots of rice seedlings. This study provides theoretical basis and data support for the application of Burkholderia sp. Y4 as a Cd-reducing and growth-promoting agent for rice in contaminated farmland.

Superior growth, N uptake and NH4+ tolerance in the giant bamboo Phyllostachys edulis over the broad-leaved tree Castanopsis fargesii at elevated NH4+ may underlie community succession and favor the expansion of bamboo.

The unbridled expansion of bamboo has imposed serious threats on ecosystem processes and functions. Considerable evidence indicates that bamboo invasions can alter plant-available soil nitrogen (N) pools and rates of N cycling, but the consequences of altered N availability for plant growth and community structure have thus far been poorly characterized. The primary soil-accessible N forms for most plants are ammonium (NH4+) and nitrate (NO3-), but plants differ in their ability to use the different N forms, and these differences can be related to their ecological characteristics and drive community structure. In this context, we evaluated the growth response, N uptake and interspecific competition in two subtropical species, Phyllostachys edulis (Carrière) J. Houzeau (Synonym Phyllostachys heterocycla Carrière) and Castanopsis fargesii Franch., dominant species of bamboo and secondary evergreen broad-leaved forests, respectively, under changing N availability in seedlings supplied with different N concentrations and NH4+/NO3- proportions, in vermiculite culture, in a controlled environment. The results show that (i) both species display an NH4+ preference at elevated N concentrations. The growth of P. edulis seedlings was strongly enhanced at increased ratios of NH4+ to NO3- especially at higher N concentrations, but to a much lesser extent in C. fargesii. (ii) NH4+ preference at the level of N uptake in both species was confirmed by the Non-invasive Micro-test Technology and by examining 15N signatures. Phyllostachys edulis had higher NH4+ net fluxes and N concentration under NH4+ treatments than C. fargesii. (iii) NH4+ at higher concentrations caused toxicity in both species as it inhibited root growth and even caused seedling death, but P. edulis had a higher NH4+-tolerance threshold (24mM) than C. fargesii (16mM). (iv) When mixed-species cultures were examined in an NH4+-rich medium, the growth of C. fargesii, but not P. edulis, was significantly inhibited compared with growth in monoculture. Therefore, P. edulis exhibited stronger plasticity and adaptation to changing N availability, whereas C. fargesii had low responsiveness and capacity to acclimate to soil N changes. Phyllostachys edulis displayed a significant competitive growth advantage compared with C. fargesii on NH4+-dominated substrates.

Comparative Analysis of Root Traits and the Associated QTLs for Maize Seedlings Grown in Paper Roll, Hydroponics and Vermiculite Culture System.

Root system architecture (RSA) plays an important role in the acquisition of both nitrogen (N) and phosphorus (P) from the environment. Currently RSA is rarely considered as criteria for selection to improve nutrient uptake efficiency in crop breeding. Under field conditions roots can be greatly influenced by uncontrolled environment factors. Therefore, it is necessary to develop fast selection methods for evaluating root traits of young seedlings in the lab which can then be related to high nutrient efficiency of adult plants in the field. Here, a maize recombination inbred line (RILs) population was used to compare the genetic relationship between RSA and nitrogen and phosphorous efficiency traits. The phenotypes of eight RSA-related traits were evaluated in young seedlings using three different growth systems (i.e., paper roll, hydroponics and vermiculite), and then subjected to correlation analysis with N efficiency and P efficiency related traits measured under field conditions. Quantitative trait loci (QTL) of RSA were determined and QTL co-localizations across different growth systems were further analyzed. Phenotypic associations were observed for most of RSA traits among all three culture systems. RSA-related traits in hydroponics and vermiculite weakly correlated with Nitrogen (NupE) uptake efficiency (r = 0.17–0.31) and Phosphorus (PupE) uptake efficiency (r = 0.22–0.34). This correlation was not found in the paper roll growth system. A total of 14 QTLs for RSA were identified in paper rolls, 18 in hydroponics, and 14 in vermiculite. Co-localization of QTLs for RSA traits were identified in six chromosome regions of bin 1.04/1.05, 1.06, 2.04/2.05, 3.04, 4.05, and 5.04/5.05. The results suggest the problem of using the phenotype from one growth system to predict those in another growth system. Assessing RSA traits at the seedling stage using either hydroponics or a vermiculite system appears better suited than the paper roll system as an important index to accelerate the selection of high N and P efficient genotypes for maize breeding programs.

Pathogenicity to Ornamental Plants of Some Existing Species and New Taxa of Phytophthora from Irrigation Water.

Eighteen isolates from 12 species of Phytophthora, including several new taxa, were tested for pathogenicity to six ornamental and four vegetable species. The following three inoculation methods were used depending on infection court targeted: vermiculite culture inoculation for roots, agar block inoculation for fruit, and zoospore inoculation for foliage. All six new taxa (P. irrigata, P. hydropathica, Dre III, Cil I, Cip-like, and Gon I) are pathogenic to one or more test plants. Specifically, taxon Cil I was identified as a growing threat to horticultural crops, particularly ornamental crops in container production nurseries. The potential host list of P. tropicalis was expanded to four new families (Apocynaceae, Asteraceae, Begoniaceae, and Fabaceae) and one additional genus within each of three existing families (Ericaceae, Cucurbitaceae, and Solanaceae). New potential hosts were also identified for other existing species of Phytophthora. The practical implications of these results in crop health management programs for both ornamental and vegetable crops locally, and for development and implementation of agricultural biosecurity programs globally, are discussed.

Eradication of Phytophthora ramorum and Other Pathogens from Potting Medium or Soil by Treatment with Aerated Steam or Fumigation with Metam Sodium

Phytophthora ramorum survived in potting media infested with sporangia or chlamydospores, allowing the pathogen to remain undetected while disseminated geographically. Chlamydospores or oospores of P. ramorum, Pythium irregulare, Thielaviopsis basicola, and Cylindrocladium scoparium produced in vermiculite culture were used to infest potting media. Infested media in plastic plug flats were treated with aerated steam mixtures from 45 to 70 °C for 30 min. In a second experiment, infested media were fumigated in polyethylene bags with a concentration series of metam sodium ranging from 0.25 to 1.0 mL·L−1. Survival of the pathogens was determined by selective baiting or direct plating the infested media on PARP selective medium. Assays indicated that all pathogens in the infested potting media were killed by aerated steam heat treatments of 50 °C or higher. Metam sodium concentrations of 1.0 mL·L−1 of medium or greater also eradicated all pathogens from the potting medium and soil. These results show that aerated steam treatment or fumigation with metam sodium can effectively sanitize soil-less potting media infested with P. ramorum or other soilborne pathogens, as well as P. ramorum-infested soil beneath infected plant containers. In addition, steam treatments to 70 °C did not melt plastic plug trays.

Survival of Phytophthora ramorum Compared to Other Species of Phytophthora in Potting Media Components, Compost, and Soil

Phytophthora ramorum, while thought to be primarily an aboveground pathogen, can be introduced into soilless potting media in the nursery industry as sporangia or chlamydospores and remain undetected while disseminated geographically. Inoculum of this pathogen, both North American (A-2 mating type) and European (A-1 mating type) isolates, was used to infest potting media components or soil, using either sporangia, chlamydospores produced in vermiculite culture, or dry infected `Nova Zembla' rhododendron (Rhododendron sp.) leaf pieces. Vermiculite chlamydospore/oospore inoculum of P. citricola, P. cactorum, and P. citrophthora were included for comparison. Survival was determined monthly by leaf disc baiting or direct plating on selective medium. Results indicated that P. ramorum survived in most media components or soil for up to 6 months when introduced as sporangia, or up to 12 months as chlamydospores. However, it was not detected at all from infected rhododendron leaf pieces by either detection method. These results show that P. ramorum can survive in potting media if introduced as sporangia or chlamydospores, and accordingly the pathogen could be disseminated geographically without being detected visually.

Plasmodesmata in onion (Alliurn cepa L.) roots: a study enabled by improved fixation and embedding techniques

Onion (Allium cepa L. cv. Ebeneezer) roots from vermiculite culture were examined with transmission electron microscopy to detect the plasmodesmata in all tissues. In young root regions, plasmodesmata linked all living cells together in all directions. In old zones, the plasmodesmatal connections of the endodermis to its neighbor tissues were not interrupted by later suberin lamella and cellulosic wall deposition. Moreover, plasmodesmata in the fully mature endodermis usually exhibited a large central cavity. In the exodermis, however, upon deposition of suberin lamellae in long cells, all plasmodesmata that initially linked them to their adjacent cells were severed. Afterwards, the long cells lost the capability of forming wound pit callose and their protoplasts began to degenerate. The mature exodermal layer was symplastically bridged to its neighbors only by the short (passage) cells that lacked suberin lamellae. Compared to the long cells, the short cells not only had thicker cytoplasm surrounding their central vacuoles but also a higher density of mitochondria and rough endoplasmic reticulum, consistent with an active involvement in the transport processes of the root. The above results were obtained by an improved, extended transmission electron microscopy procedure devised to analyze plasmodesmata in cells with suberin lamellae. By prefixing root tissues in glutaraldehyde and acrolein, all cells were well preserved. Postfixation was carried out in osmium tetroxide at a low concentration (0.5%). Following dehydration in acetone and transfer to propylene oxide, infiltration with Spurr's resin was accomplished by incubating samples in the accelerator-free mixture for 4 days, then infiltrating samples in the accelerator-amended mixture for additional 4 days.

Renodulation and characterization of Rhizobium isolates from cicer milkvetch (Astragalus cicer L.)

In 1993 and 1994, 12 bacterial isolates were isolated from root nodules of cicer milkvetch (Astragalus cicer). In the tests for nodulation of A. cicer by these bacterial isolates, five were found to form hypertrophic structures, while only two formed true nodules. These true nodules were formed in a sterilized soil system. This system might be able to act as a DNA donor to provide residual DNA to other microbes in the soil. The rhizobial isolates were thought to have lost genetic material crucial to nodulation during the isolation process. This hypothesis was supported by an experiment in which isolate B2 was able to nodulate A. cicer in vermiculite culture after being mixed with heat-killed rhizobia, Rhizobium leguminosarum bv. trifolii and R. loti. The nodulation would not occur in vermiculite culture system without the heat-killed rhizobia. Based on the biochemical data, the B2 and 9462L, which formed true nodules with A. cicer, were closely related. The rhizobia type cultures that nodulate A. cicer include Bradyrhizobium japonicum, Rhizobium leguminosarum bv. trifolii, R. leguminosarum bv. viceae, and R. loti. All of these rhizobia were from different cross-inoculation groups. The B2 and 9462L isolates could only nodulate Medicago sativa, Phaseolus vulgaris, and Melilotus officinalis, but not these species within the genus from which they were isolated: Astragalus. The traditional cross-inoculation group concept obviously does not fit well in the classification of rhizobia associated with Astragalus. The rhizobia isolated from A. cicer can be quite different, and the rhizobia able to renodulate A. cicer also quite diverse.

Mineralization of 2,4- dichlorophenol by ectomycorrhizal fungi in axenic culture and in symbiosis with pine

Experiments were conducted to determine if two ectomycorrhizal fungi ( Paxillus involutus and Suillus variegatus) could degrade 2,4- dichlorophenol, both in axenic liquid culture and during symbiosis with a host tree species Pinus sylvestris. Both fungi readily degraded 2,4- dichlorophenol in batch culture with similar rates of mineralization on a biomass basis. Up to 17% of the 2,4- dichlorophenol was mineralized over a 17 day period. Growth of the fungi in symbiosis with P. sylvestris stimulated greater mineralization than when fungi were grown in absence of the host. S. variegatus was more efficient than P. involutus (in the presence of P. sylvestris) at mineralizing 2,4- dichlorophenol. Mineralization in vermiculite culture was greatly reduced compared to liquid culture. Only 3% of the 2,4- dichlorophenol was mineralized after 13 days in vermiculite culture for the most efficient degrading treatment.

Salinity effects on growth analysis and nutrient composition in four grain legumes‐rhizobiumsymbiosis

Abstract The effect of salinity on growth response, nitrogen (N) fixation and tissue mineral content was investigated for four legumes: faba bean (Vicia faba L), pea (Pisum sativum L), soybean (Glycine max L), and common bean (Phaseolus vulgaris L). Plants were grown in a vermiculite culture system supplied with a N‐free nutrient solution with the addition of 0, 50, and 100 mM NaCl. Plants were harvested at the beginning of the flowering period and the dry weights of shoots and roots and acetylene reduction activity (ARA) were evaluated at the same time plant tissues were analysed for N, potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) contents. The depressive effect of saline stress on ARA of nodules was directely related to the salt induced decline in dry weight and N content in shoots. Growth inhibition by NaCl treatments was greater for the pea than for other legumes, whereas the soybean was the most salt‐tolerant Saline stress also affected the N content in shoots and roots. In general th...

Effect of nacl salinity on growth and distribution of sodium and some macronutrient elements in soybean plant

Abstract Two pot experiments were carried out with soybeans using vermiculite and water culture as growth media to study: a) the effect of NaCl salinity on the growth and cationic relations in the plant and b) the effect of NaCl elimination on the cationic relations in the salt-affected plants. The results obtained were as follows. 1. Salinity depressed the plant growth, particularly pods at the filling stage due to the low efficiency of pod yield production % (dry matter distribution %) in the salt-affected plants. 2. In the salt-affected plants, the stems were found to be the major sink of accumulated sodium, while the leaves exhibited the lowest Na concentration among the different plant parts. 3. After NaCl elimination from the growth medium, Na concentration in the salt-affected plants was markedly decreased particularly in the leaves and pods. In contrast, Na concentration in the shoots was slightly increased. 4. Salinity generally increased the concentrations of K, Ca, and Mg in the leaves and decr...

The influence of two culturing techniques on toxicity of four chemicals in Arabidopsis

Plots of Arabidopsis thaliana L. (Heynh.) plants were grown in two hydroponic systems, one using a solid rooting support media (vermiculite) and the other a flowing solution culture. Both were tested with various concentrations of bromacil (5-bromo-3-sec-butyl-6-methyluracil), dichlobenil (2,6-dichlorobenzonitrile), copper sulfate (CuSO4·5H2O) and 3-aminotriazole. The effects on biomass production were compared. Plants treated with bromacil at concentrations up to 0.05 mg l(-1) were similarly reduced in growth in both culture methods. However, the toxic effects of dichlobenil, copper sulfate and 3-aminotriazole were different for both culture methods. Dichlobenil decreased plant growth in the solution culture at lower concentrations than in the vermiculite system. All aspects of growth were suppressed in the solution culture while the vegetative weight was unaffected in the vermiculite culture. Plants treated with 20 mg l(-1) copper sulfate in solution culture yielded mean seed weight of 1.2 g/plot compared to 3.1 g/plot when treated with the same concentration in the double-plot system. Plants treated with 0.5 mg l(-1) 3-aminotriazole in solution culture produced no seed, while plants with the same nominal concentration in the double-pot method produced a mean seed weight of 6.5 g/plot. Solution culture testing was generally more sensitive and since roots were bathed directly in a solution of known pH, nutrient level and chemical concentration, the test conditions were more accurately defined.

Autointoxication in root exudates ofAsparagus officinalis L.

Effects of asparagus root exudates on the growth and nutrient uptake of the seedlings of the same species in vermiculite culture were investigated. The phytotoxicity of collected root exudates of asparagus was tested by asparagus seed bioassay. Root exudates were washed from the donor pot to the acceptor pot. The height and number of stalks of asparagus seedlings of three varieties. Mary Washington, California 309 and 711 receiving root exudates were significantly reduced. No significant difference was observed in the growth of seedlings among these three varieties. N, P and K contents in the tops of asparagus seedlings were unaffected by root exudate treatments. The growth of asparagus radicle and shoot was inhibited by the root exudates collected from a resin trapping system. Bioassay results obtained with root exudates where the inhibition of shoot growth by root exudate was greater than that of root growth corresponded to the result in vermiculite culture. These data suggested that asparagus is an autoinhibited species which root exudates inhibit its own growth. Autointoxication as a possible mechanism for the yield decline and missing of plants in the replanting of asparagus in the tropics is discussed.

Phenotypic Thermal Stability of Rhizobitoxine‐induced Chlorosis and the Nodulation Controlling Gene, rj11

The rj1 gene in soybeans (Glycine max L. Merrill), prevents nodulation with a broad range of strains of Rhizobium japonicum. Strains of R. japonicum that produce rhizobitoxine induced foliar chlorosis can nodulate rj1 plants in sand or vermiculite culture in the greenhouse. This study was undertaken to determine the effects of temperature on the expression of chlorotic symptoms and nodulation of rj1 plants, and to clarify the relationship between nodulation and chlorosis. Tests with plants cultured in Leonard jars in environmental control chambers maintained at 21, 27, and 32 C indicated that temperature modified the nodulation response of Clark rj1 soybeans with the chlorosis inducing strains 61 and 76. Chlorotic symptoms were beast evident at 21 C. Strain 61 produced good nodulation on rj1 plants at 21 C, but exhibited no induction of chlorosis at that temperature on the cultivar ‘Hawkeye.’ Strain 76 produced strong chlorotic symptoms on both the cultivars Hawkeye and ‘Peking’ at 32 C, but only a low level of nodulation with the rj1 plants. This differential effect of temperature on these two processes suggested that, while rhizobitoxine is correlated with both processes, separate control mechanisms with different temperature optima govern their expression.Increasing the temperature from 21 to 32 C mitigated the expression of the ineffective nodulation response of the Rj1 gene with strain 61 in the cultivar Peking. Despite the low level of nodulation (3.6 nodules per plant) of strain 61 with Peking at 32 C, chlorotic symptoms were clearly apparent.

Nodulation of soybeans carrying the nodulation-restrictive gene, rj1, by an incompatible Rhizobium japonicum strain upon mixed inoculation with a compatible strain

The rj1 gene in soybeans prevents nodulation by most strains of Rhizobium japonicum. Several strains, however, are known to nodulate rj1 plants in vermiculite or sand culture. Pure broth cultures of one of these strains (61 NalR) and a strain producing the typical non-nodulating response with rj1 (I-110 ARS) were mixed and used as inoculum on Clark rj1 soybeans in a growth chamber experiment. Both strains carried drug resistance markers and were identified using selective media. Analysis of the nodules formed indicated that 32% of the nodules contained both strains, 36% contained only the usually non-nodulating strain I-110 ARS, and 32% contained the usually infective strain (61 NalR). These results indicate that under conditions of high inoculum density the roots of Clark rj1 plants did not distinguish between Rhizobium strains 61 NalR and I-110 ARS. Subsequent tests with Rhizobium isolates from the nodules containing only strain I-110 ARS indicated that these rhizobia had not undergone a permanent genetic change in nodulation potential but were infective only because of temporary association with strain 61 NalR.

Evaluation of oxfendazole against natural infections of gastrointestinal nematodes in Nigerian calves

The efficacy of oxfendazole was tested in naturally infected Sokoto-Gudali calves at a dosage of 2.8 mg per kg. At this dosage level, oxfendazole showed 100 per cent efficacy against adult and immature forms of Haemonchus spp, Trichostrongylus spp, Bunostomum phlebotomum and Oesophagostomum radiatum. Although efficacy of 100 per cent was recorded for the adult form of Cooperia spp, only 48 per cent reduction was recorded for its immature stages. Similarly, a percentage reduction of 75 was recorded for adult Trichuris spp. No larvae hatched out of a seven-day vermiculite culture of faeces collected from the treated calves 24 h after treatment.

Phytophthora drechsleri: Pathogenicity Testing and Determination of Effective Host Range

Pathogenicity tests with Phytophthora drechsleri Tucker chlamydospores and different flooding times were conducted on 15 weed and 17 cultivated plant species. Lucerne, safflower and skeleton weed were the only plants that showed a marked response to the pathogen. Lucerne, safflower and soya bean plants were inoculated with agar culture, vermiculite culture or chlamydospores, and their reaction was shown to vary with the type of inoculum used. On the basis of these results, the concept of pathogenicity testing and the results on which the known host range of this fungus is based are examined. It is argued that conclusions drawn from pathogenicity tests are often question- able if the inoculation techniques employed bear little similarity to what may occur in the field. Suggestions for future pathogenicity tests are made.

Evidence that toxins are not the causal factors of the specific apple replant disease*

SUMMARYExperiments were made to test the hypothesis that a toxin produced by or from apple roots is the causal factor of specific apple replant disease. In sand and vermiculite culture, apple leachates were not harmful to the growth of apples. In the field, apples exerted no effects on neighbouring apples other than competition effects. In pot and field experiments, the addition of apple root residues to fresh (unused) or fumigated soil depressed the growth of both apple and cherry test plants; similar additions to used (‘replant’) apple soil, however, improved the growth of apple, but not of cherry, test plants. It is concluded that specific apple replant disease is not caused by a toxin derived from root residues. It is suggested that the cause may rather be a rhizosphere microorganism.