Cross-inoculation Studies Research Articles

Cercospora beticola causes leaf and stem spots of New Zealand spinach (Tetragonia tetragonoides) in Brazil

New Zealand (NZ) spinach (Tetragonia tetragonoides) is an important leafy vegetable crop in Brazil and other countries. This plant is used as a substitute for common spinach because it is rustic and tolerant to tropical and subtropical environmental conditions. It is often affected by a leaf and stem spot disease, which increases in severity during the warm climatic periods. Cercospora tetragoniae has been reported as the cause of this disease, but this is based on an early description of a Cercospora-like species on this host in Argentina, first named Cercosporina tetragoniae but later recombined into Cercospora. In the present study, isolates of Cercospora-like fungi were obtained from NZ spinach and beetroot plants in Brazil, and a multigene molecular study including the act, cal, gapdh, his3, ITS, and tef1-α regions was carried out to identify the causative pathogen. Additionally, morphological and cross inoculation studies were conducted with isolates obtained from diseased plants. The pathogen was confirmed as Cercospora beticola, a common and harmful pathogen of beetroot (Beta vulgaris). Cross-inoculations of isolates obtained from NZ spinach and beetroot showed that the isolates are infective to both hosts. This increases knowledge of epidemiology and management of this important disease. Several attempts to re-collect samples from the type locality in Argentina failed. NZ spinach is no longer grown at La Plata (Argentina), the type locality of C. tetragoniae. Therefore, the task of re-collecting the pathogen is still pending, for epitype designation and for a full clarification of the taxonomic status of C. tetragoniae. The possibility of the pathogen being seed-transmitted has been assessed, and evidence obtained justifies further assessment of this aspect.

CHARACTERIZATION AND COMPARATIVE RESPONSE OF RHIZOBIA ISOLATES FROM ROOT NOODLES OF SELECTED WEED SPECIES AND SOYBEAN (Glycine max) TO ENVIRONMENTAL FACTORS

Screening and selecting the most effective strains of rhizobium is important for biological nitrogen fixation. To determine the effects of environmental factors on rhizobia strains associated with some selected leguminous weed species, rhizobia strains isolated from root nodules of five weed species (Mimosa pudica, Crotolaria retusa, Desmodium triflorum, Canavalina ensiformis, Stylosanthes spp.) were subjected to varying temperature, salinity, and pH in the laboratory. Results indicated better growths at temperatures of 30 and 370C compared to the temperature of 250C. Results further showed that microbial growth was optimal at 1.5% salt concentration. Optimum growth was also obtained at the pH range of 5 and 8. The study further revealed by a series of morphological and biochemical tests that all the strains were gram-negative, rod-shaped, and mucous producing. Rhizobia strains from leguminous weeds were found to exhibit faster growth than the strain nodulating soybean in all the conditions to which they were subjected. A cross inoculation study was therefore recommended to access the compatibility of these rhizobial strains from the wild with cultivated leguminous plant species.

Plant neighborhood shapes diversity and reduces interspecific variation of the phyllosphere microbiome.

Microbial communities associated with plant leaf surfaces (i.e., the phyllosphere) are increasingly recognized for their role in plant health. While accumulating evidence suggests a role for host filtering of its microbiota, far less is known about how community composition is shaped by dispersal, including from neighboring plants. We experimentally manipulated the local plant neighborhood within which tomato, pepper, or bean plants were grown in a 3-month field trial. Focal plants were grown in the presence of con- or hetero-specific neighbors (or no neighbors) in a fully factorial combination. At 30-day intervals, focal plants were harvested and replaced with a new age- and species-matched cohort while allowing neighborhood plants to continue growing. Bacterial community profiling revealed that the strength of host filtering effects (i.e., interspecific differences in composition) decreased over time. In contrast, the strength of neighborhood effects increased over time, suggesting dispersal from neighboring plants becomes more important as neighboring plant biomass increases. We next implemented a cross-inoculation study in the greenhouse using inoculum generated from the field plants to directly test host filtering of microbiomes while controlling for directionality and source of dispersal. This experiment further demonstrated that focal host species, the host from which the microbiome came, and in one case the donor hosts' neighbors, contribute to variation in phyllosphere bacterial composition. Overall, our results suggest that local dispersal is a key factor in phyllosphere assembly, and that demographic factors such as nearby neighbor identity and biomass or age are important determinants of phyllosphere microbiome diversity.

Differential gene responses in different varieties of pomegranate during the pathogenesis of Xanthomonas axonopodis pv. punicae.

The online version contains supplementary material available at 10.1007/s13205-021-02721-y.

Isolation, identification and confirmation of Foliar nematode, Aphelenchoides besseyi association with Dendrobium Orchid under Polyhouse condition

Dendrobium orchid, Dendrobium nobile, is one of the most widespread ornamentals. Besides durability and high keeping quality, its fragrant, waxy and variable coloured flowers are having a high market demand. Dendrobium orchid was found to be one of the favourable hosts for foliar nematode, Aphelenchoides besseyi. The cross inoculation study confirmed the association of Foliar nematode, A. besseyi in Dendrobium. The nematode was found to remain active on plants round the year under polyhouse condition with high temperature and relative humidity affecting the quantity and quality of flower appreciably.

Perpetuation and host range of Oidium euonymi-japonici causing powdery mildew of Euonymus japonicus in Kashmir valley, India

The pathogen Oidium euonymi-japonici (anamorph) causing powdery mildew of Euonymus japonicus in Kashmir valley overwintered asexually as mycelium on intact infected twigs which started producing conidia in the 4th week of February and continued till ending October during both the years of study 2013 and 2014. The pathogen ceased to produce conidia from the 1st week of November to 3rd week of February, 2013–2014 and 2014–2015. On intact-overwintered infected twigs, maximum conidial production and viability was observed during 1st week of April and 1st week of August in both the years. However, no conidial formation was observed on the twigs, kept 10 cm deep in the soil. The cross inoculation study revealed that inoculum from Euonymus japonicus successfully infected all the other Euonymus genotypes tested but failed to infect the weeds and other test hosts and vice versa.

Phylogeny and genetic diversity assessment of Ensifer strains nodulating Senegalia (Acacia) senegal (L.) Britton. in arid regions of Western Rajasthan, India

The tree Senegalia (Acacia) senegal is well adapted to soils of arid regions having a vital role in reforestation and increasing soil fertility through biological nitrogen fixation in addition to its utility as edible seeds and gum. Fifty-nine root nodule bacterial (RNB) strains were isolated; characterized at phenotypic and genotypic level; and host range was studied. The Senegalia-RNB strains were able to grow up to 3% NaCl and on a wide range of pH (5–11) with optimum growth at alkaline pH showing their adaptation to alkaline desert soil. The carbon utilization pattern of Senegalia-RNB strains was significantly different from existing closely related type strains of Ensifer. The PCR-RFLP (ARDRA) as well as RAPD patterns revealed considerable genetic diversity among the strains forming distinct genetic groups. The 16S rRNA phylogeny of selected six (AS11, AS18, AS27, AS34, AS50 and AS53) strains showed that they belong to fast growing species of Ensifer with few being similar to the previously described Ensifer strains from Vachellia jacquemontii and Vachellia leucophloea from Thar Desert of India. The symbiotic (nifH and nodA) gene phylogeny showed incongruence with that of 16S rRNA gene (species) phylogeny suggesting HGT incidences under hot-arid and alkaline environment. The Senegalia-Ensifer strains possessing novel symbiotic genes could effectively cross-nodulate species of Vachellia (V. jacquemontii, V. leucophloea and V. nilotica) but failed to nodulate the crop Vigna radiata. Multi locus sequence analysis (MLSA) is required to determine novelty of these Ensifer strains and more cross-inoculation studies will help in understanding their potential use as inoculums in nursery practices for reforestation program in arid and semi-arid regions.

Nodulation Responses of Four Food Crop Legumes to Cross-inoculation in the Guinea-savannah (Ngaoundere-cameroon) and Sudanian (Sarh-Chad) Zones

A cross-inoculation study on groundnut (Arachis hypogaea L.), bambara groundnut (Vigna subterranea L.), cowpea (Vigna unguiculata L.), and soybean (Glycine max L.) was carried out to screen potentially hight nodulating and nitrogen fixing Rhizobium strains suitable for important crops legumes in the Adamawa region (Cameroon) and middle-Chari region (Chad). The experiment was displayed in a complete Randomised Block with 6 forms of inoculation representing the treatments, each of which was replicated four times. An experimental field consisted of 4 blocks, each rcorresponding to a specific crop legume, which was submitted to each of the following treatments: the control (Ctrl); Groundnut Rhizobium (GR); Cowpea Rhizobium (CR); Soybean Rhizobium (SR); bambara groundnut Rhizobium (BR); and the mixture of these 4 rhizobia (MR). The cross-inoculation types consisted of taking Rhizobium isolates from each crop legume and coating with each of the seed crop before sowing (GR/cowpea/soybean/bambara groundnut, CR/groundnut/soybean/ bambara groundnut, BR/cowpea/soybean/groundnut, SR/cowpea/groundnut bambara/ groundnut, MR/groundnut/cowpea/soybean/Bambara groundnut). Cross-inoculation significantly (p = 0.001) improved the number, efficiency and dry weight of the nodules in all the crop legumes. The responses to nodule efficiency differed from one treatment or host plant species to another. In our investigation to the speculation whether one rhizobial strain can nodulate several crop legumes, we found out that groundnut can be inoculated with SR/BR in Cameroon, or CR/BR in Chad, whereas CR/BR/MR were the best trains to be associated with cowpea both in Cameroon and Chad. Farmer could also use CR/SR in Cameroon and SR/BR in Chad to inoculate soybean, or inoculate bambara groundnut in Cameroon and Chad with GR/BR. All the four crop legumes are thus considered as are promiscuous since each can form symbiotic associations with rhizobia from many other hosts. Selecting these highly effective rhizobia is an important step toward commercial inoculants production for biological nitrogen fixation research in our developing world context.

Assessment of affinity and specificity of Azospirillum for plants

Azospirillum spp. are the most studied plant growth-promoting bacteria (PGPB). The genus represents a common model for plant-bacteria interactions. This genus was initially isolated and tested on cereals and was subsequently commercialized. Despite claims of plant specificity, particularly towards cereals, data over the past 40 years does not appear to substantiate claims of such specificity/affinity of Azospirillum species. Consequently an evaluation of the specificity/affinity of the genus Azospirillum across all plants, in general, and cereals, in particular, was undertaken. Although the majority of studies focused on cereals, Azospirillum spp. increase growth of 113 plant species across 35 botanical families, including 14 species of cereals. Amongst Azospirillum spp., several well studied strains have been effective in several plant species, making these organisms potentially valuable for further study. This review demonstrates that azospirilla are not cereal-specific at the genus and species levels. Azospirillum serves as a general PGPB to every plant species tested so far. Given the paucity of widespread screening, affinity of strains to a plant genotype, cultivar, or plant species cannot be overruled. Definitive conclusions concerning such specificity require molecular and cross-inoculation studies, using various strains of bacteria, and re-isolation after growth of the plants in different plant species. (203 words).

First Report of Puccinia psidii Caused Rust Disease Epiphytotic on the Invasive Shrub Rhodomyrtus tomentosa in Florida.

Rhodomyrtus tomentosa (Aiton) Hassk. (downy-rose myrtle, family: Myrtaceae), of South Asian origin, is an invasive shrub that has formed monotypic stands in Florida (3). During the winter and spring of 2010 through 2012, a rust disease of epiphytotic proportion was observed on young foliage, stem terminals, and immature fruits of this shrub in natural areas of Martin and Lee counties, Florida. Expanding leaves and succulent stems developed chlorotic flecks on the surface that developed into pustules and ruptured to discharge urediniospores. Symptomatic leaves and stems developed severe necrotic spots and resulted in tissue distortion, defoliation, and stem dieback. Based on symptoms and urediniospore morphology and dimensions (17.7 to 26.1 [22.1 ± 0.3] × 14.7 to 21.1 [17.7 ± 0.2] μm; n = 51) (4), the causal agent was identified as Puccinia psidii Winter; teliospores were not observed in samples since it does not produce these spore stages below 20°C ambient temperature (1). This identification was confirmed by a GenBank BLAST of internal transcribed spacer (ITS) sequences (Accession Nos. KC607876 and KC607877) that showed 99% identity with 42 sequences of P. psidii from diverse host species and locations. P. psidii is believed to be of neotropical origin and has a host range of 129 species in 33 genera within Myrtaceae (2). However, P. psidii caused disease of downy-rose myrtle has not been previously reported in Florida, even though severe infections occurred on another invasive tree, Melaleuca quinquenervia (Cav.) S.F. Blake (3), growing in adjacent areas. In December 2011, urediniospores were collected from downy-rose myrtle, established in aqueous suspension (45,000 spores/ml), and spray inoculated on potted downy-rose myrtle plants (n = 3), which were maintained in 100% ambient humidity, at 20°C, with a 12-h light cycle for 72 h. Plants mock-inoculated with water served as the negative control. Disease symptoms, including chlorotic flecks and raised surfaces, appeared on leaf lamina in 3 to 6 days on P. psidii-inoculated plants, while control plants remained symptomless. Raised surfaces developed into distinct pustules and eventually erupted to discharge urediniospores within 6 to 12 days of inoculation. Tests were repeated once during March and April of 2012 with the same results. The latent and incubation periods reported herein are within the previously reported range for P. psidii (2,4). To our knowledge, this is the first confirmed report of P. psidii epiphytotic on downy-rose myrtle populations in Florida. The recent occurrence of P. psidii epiphytotic on downy-rose myrtle raises critical questions as to why this myrtle rust disease is so severe and widespread on this host after decades of presumed exposure to P. psidii in Florida. Because this rust pathogen has emerged as a major invasive threat to many myrtaceous species around the world, further genotyping and cross-inoculation studies are needed to determine the host specificity and potential origin of the P. psidii isolates derived from downy-rose myrtle (2).

Study on Differential Response of Pyricularia grisea Isolates from Rice, Finger Millet and Panicum sp. with Local and Alien Media, and Their Host Range

Blast (Pyricularia grisea) is an economically important disease of rice and finger millet in Nepal. Isolates of the fungus from different hosts differed in their response in media for mycelial growth and sporulation. Radial mycelial growth (RMG) and days of sporulation (DOS) of P. grisea were studied by culturing three fungal isolates from rice, finger millet and Panicum sp. on six different media: prune agar (PA), oat meal agar (OMA), potato dextrose agar (PDA), finger millet leaf decoction agar (FLDA), finger millet polish agar (FPA) and finger millet meal agar (FMA). The highest RMG was found in the isolates from finger millet and the lowest in the isolates from rice. The shortest DOS (1 week) was found in the isolate from rice and the longest (>2 weeks) in the isolate from finger millet. Among the different media used, PA and OMA were found to be the best for mycelial growth and sporulation of the isolates both from rice and finger millet. The shape, color and compactness of the fungal colonies varied with the media and isolates used. Cross inoculation studies showed that the fungus isolates from rice were able to infect all the plant species (rice, finger millet, Panicum sp., Eleusine indica and Setaria sp.) while isolates from finger millet were only able to infect three plant species (E. coracana, Setaria sp. and E. indica). This shows that the weed management is more important in finger millet fields than in rice field to manage the blast disease; and growing of rice adjacent to finger millet field is dangerous for blast epidemics in finger millet since rice serves as the source of inoculums. Nepal Journal of Science and Technology Vol. 13, No. 2 (2012) 7-14 DOI: http://dx.doi.org/10.3126/njst.v13i2.7707

Phylogenetic multilocus sequence analysis identifies seven novel Ensifer genospecies isolated from a less-well-explored biogeographical region in East Africa

The diversity of 71 rhizobial strains belonging to the genus Ensifer, isolated from root nodules of woody legumes growing in southern Ethiopia, was studied using multilocus sequence analysis (MLSA) and phenotypic approaches. Phylogenetic analyses based on core genes revealed that 43 strains were clustered in seven distinct and consistent positions (genospecies I-VII), while another 25 strains were also distinct but were discrepant in their placement on the different gene trees. The remaining three strains occupied the same phylogenetic branches as defined Ensifer species and thus were not distinct. Irrespective of their chromosomal background, the majority of the test strains were highly related with respect to their nifH and nodC gene sequences, suggesting that these symbionts might have acquired these genes recently from a common origin. On the nifH phylogenetic tree, the branch containing the test strains and reference species isolated from woody legumes in Africa was clearly separate from those isolated outside the continent, suggesting that these symbionts have a long history of separate evolution within Ensifer for this gene. A cross-inoculation study showed that our strains were capable of eliciting effective nodulation on the homologous host and on other host species. This suggests a potential to improve nitrogen fixation by selecting for broad-host-range inoculants. Our study confirms the presence of a wide diversity of Ensifer in East Africa and, while contributing to the general knowledge of the biodiversity within the genus, also highlights the need to focus on previously less-well-explored biogeographical regions to unravel as-yet-unidentified rhizobial resources.

MORPHOLOGICAL AND PHYLOGENETIC CHARACTERIZATION OF PESTALOTIOPSIS IN RELATION TO HOST ASSOCIATION

Cross-inoculation studies of fifteen Pestalotiopsis isolates collected from different hosts and locations revealed that the fungus is a non specific pathogen. Isolates were able to attack apple, avocado, date-palm, guava, mango and pomegranate causing leaf spot and fruit rot. Disease severity and disease symptoms varied according to plant species. Guava plants was the most susceptible host, all being attacked by tested isolates resulting in brown leaf spot followed by pomegranate, while date palm was least affected. Avocado isolate (P6) was more aggressive on all tested plants, while date palm isolate (P12) was weakest. Six primers were used to determine the degrees of similarity among the tested isolates through RAPD - PCR. Isolates from the same host were not phylogenetically close - related. A close phylogenetic relationship among isolates possessing similar morphological characters was observed

Cross inoculation studies: Response of Vigna mungo to inoculation with rhizobia from tree legumes growing under arid Environment

Cross-inoculation experiments were conducted in the greenhouse to test the rhizobia isolated from nodules of seven tree legumes for their effectiveness in Vigna mungo plants. The tree legumes included Albizia lebbeck, Dalbergia sissoo, Leucaena leucocephala, Pithecellobium dulce, Prosopis cineraria, Prosopis glandulosa and Prosopis juliflora, all growing under arid environment. Rhizobia from these legumes formed nodules on the roots of Vigna mungo except isolates from Albizia lebbeck. Dry weight and nitrogen contents of Vigna mungo plants increased significantly (P<0.05) in response to cross inoculation as compared to uninoculated control. Rhizobia from Leucaena leucocephala and Prosopis glandulosa showed significant increase in dry weight (P<0.05) and nitrogen contents (P<0.05) than other inoculated treatments. The natural rhizobia of wild tree legumes growing under arid environment show higher tolerance to prevailing adverse conditions like salt stress, elevated temperatures and drought. These rhizobia may be used to inoculate wild as well as crop legumes cultivated in reclaimed desert lands. These rhizobia may have specific traits that can be transferred to other rhizobia through genetic engineering tools. The cross infection of agriculturally important legumes with isolates from wild legumes may prove a useful means of increasing nitrogen contents within these plants.

Host range and cross inoculation studies on Macrophomina phaseolina from sunflower

M. Phaseolina isolated from sunflower infected all the 22 plants tested but failed to infect finger millet, pearl millet, haryali, nutgrass, mookkuthipoondu and saranai. M. phaseolina isolates from sunflower, blackgram, greengram, cowpea, sesame and cotton were cross pathogenic. Sunflower and blackgram isolates were the most aggressive while those of sesame and cotton were the least virulent. There was a positive correlation between M. phaseolina infection and the crop plants belonging to botanical families Fabaceae, Pedaliaceae, Asteraceae and Malvaceae.

Conspecificity of Endothia eugeniae and Cryphonectria cubensis: a re-evaluation based on morphology and DNA sequence data

Cryphonectria cubensis and Endothia eugeniae are fungal pathogens of Eucalyptus and clove that were reduced to synonymy on the basis of results of crossinoculation studies, isozyme analysis, cultural studies, and morphology. A previous phylogenetic study on Cryphonectria, based on sequence variation in the ITS region of the ribosomal RNA operon, also supported the conspecificity of C. cubensis and E. eugeniae, but was based on only one E. eugeniae isolate. New collections from clove in Brazil and Indonesia have become available, providing the opportunity to reconsider the conspecificity of C. cubensis and E. eugeniae. The occurrence of C. cubensis on clove was confirmed based on morphological comparisons and phylogenetic analyses of ribosomal DNA and β-tubulin gene sequence data. In addition to C. cubensis, other fungi morphologically similar to Cryphonectria species on the basis of their orange stromata were present on some clove specimens, but no isolates were available for these fungi. Furthermore, some isolates, for which no herbarium material exists, grouped separately from the C. cubensis clade and closer to the Cryphonectria clade. The presence of more than one closely related fungus on clove raises questions relating to the legitimacy of the synonymy of E. eugeniae and C. cubensis. Based on the presence of C. cubensis on the type specimen of E. eugeniae, we recognize the synonymy of the two fungi but provide evidence that other fungi, more closely related to Cryphonectria spp. than to C. cubensis, are present on clove.

First Report of Verticillium dahliae Causing Artichoke Wilt in California.

In mid-August 1998, artichoke (Cynara scolymus L.) plants of cultivar Imperial Star in a field in the Salinas area of the central coast of California developed wilt symptoms. The plants were stunted with chlorotic, drooping, and dried leaves near the bottom and middle of the plants as previously described in Italy (1). Diseased plants produced smaller edible buds and, in severe cases, buds were discolored with dried outer bracts. Roots exhibited the characteristic vascular discoloration of Verticillium infection. In one part of the infested field, artichoke was near harvest with 85% of plants showing wilt symptoms with vascular discoloration whereas the other part had a 60-day-old crop with 98% of plants infected. Yield in the field was reduced by as much as 50%. Verticillium dahliae was isolated from infected plant samples on NP-10 medium (2), and isolates were single spored before storing on potato dextrose agar at 4°C. Identity of the pathogen was confirmed based on colony morphology and formation of microsclerotia. In root-dip inoculation tests in the greenhouse, two V. dahliae isolates from artichoke infected 1-month-old artichoke seedlings that wilted within 6 weeks of inoculation. V. dahliae was reisolated from plants showing vascular discoloration. Cross-inoculation studies revealed that artichoke isolates caused a moderate level of disease in lettuce, but only a trace of vascular discoloration in cauliflower. Lettuce isolates caused a severe wilt in artichoke. Cauliflower isolates did not cause wilt in lettuce and caused only slight vascular discoloration in artichoke. This is the first report of a Verticillium wilt of artichoke in California.

Variations in seedling growth, nodulation and nitrogen fixation of Acacia nilotica inoculated with eight rhizobial strains

Nodulation, nitrogen fixation and growth in seedlings of a Senegalese provenance of Acacia nilotica subsp. tomentosa, inoculated with eight different Rhizobium strains isolated from various African Acacia species, were measured. The Rhizobium strains were markedly different in their ability to induce functional nodules suggesting, in view of previous reports of cross-inoculation studies, that strain specificity at subspecies and/or provenance level may occur in A. nilotica. Three strains isolated from Acacia species other than A. nilotica were non-invasive. Of two strains isolated from A. nilotica subsp. kraussiana, one strain induced formation of ineffective nodules, while the other induced formation of effective nodules displaying a mean acetylene reduction rate, on nodules from 10-week-old seedlings, of 57.7 μmol g −1 h −1. This is more than ten times higher than previously reported for an unspecified subspecies of A. nilotica in a field trial in India and compares favourably with results reported from other nitrogen-fixing tree species widely promoted for use in agroforestry such as Leucaena leucocephala. Three re-inoculated strains induced the formation of partially effective nodules. Seedlings with effective nodules had 50% larger dry mass and more than double the total nitrogen content of non-nitrogen fixing seedlings. Variability in total dry weight, nodule dry weight and total nitrogen content of effectively nodulated seedlings were high and strongly positively correlated ( r=0.88 to 0.99) indicating considerable potential to improve initial growth rates and nitrogen fixation in A. nilotica through selection.

Patterns of Root Colonization in Epacridaceous Plants Collected from Different Sites

Root colonization was studied in ten species of the Epacridaceae at three sites in Victoria by morphological and cross-inoculation experiments. The sites and genera chosen were Cranbourne [ Epacris impressaLabill. and Leucopogon ericoides(Smith) R. Br.] and Rye [ L. parviflorus(Andrews) Lindley] on the Mornington Peninsula, and the Grampians [Astroloma conostephioides(Sond.) Benth., A. humifusum(Cav.) R. Br., A pinifolium(R. Br.) Benth, Brachyloma daphnoides(Smith) Benth., E. impressa, E. impressavar. grandifloraBenth. and Styphelia adscendensR. Br.] in western Victoria. For morphological studies, samples of roots from each species at each site were cleared and stained and examined microscopically. For cross-inoculation studies, cuttings from each site were struck in potting medium inoculated with soil from the same and other sites. The ericoid mycorrhizae in the roots of plants found at or grown in Cranbourne and Rye soils were similar. Both were significantly different from the internal hyphae found in the roots of plants found at or grown in Grampians soils, which were three times larger in diameter and formed dense coils which filled the host cell and invaded adjacent epidermal cells. This suggests that more than one fungus is involved in the relationships, that the Mornington Peninsula sites had a different fungus from the Grampians site and that host specificity is low. Vesicular structures were also found commonly on plants at the Grampians site, in contrast with other sites.

Actinorhizal host-specificity of Chinese Frankia strains

Cross-inoculation studies of numerous Frankia strains of Asian origin, primarily Chinese, were undertaken to determine whether previously described host specificity groups (HSG) were valid. Each strain was inoculated onto seedlings of Alnus glutinosa, Casuarina cunninghamiana, Elaeagnus angustifolia and Myrica cerifera in solution culture, and the presence of nodules scored after eight weeks. All strains tested fell into three of the four HSG descriptions of Baker (1987). Our results indicate that among pure cultured Frankia strains derived from Asia there exists less diversity than those of North America and Europe, in regard to host specificity.