Vladimir Vujanovic

Negative feedback on a perennial crop: Fusarium crown and root rot of asparagus is related to changes in soil microbial community structure

The dynamic equilibrium of an ecosystem is driven by mutual feedback interactions between plants and soil microorganisms. Asparagus exerts a particularly strong influence on its soil environment through abundant production of persistent phenolic acids, which impact selectively soil microorganisms and may be involved in Fusarium crown and root rot (FCRR) of asparagus. In a survey of 50 asparagus plantations of the province of Québec, we found that FCRR was associated with a profound cultivar-specific, reorganization of the soil microbial community, as revealed by phospholipid fatty acid (PLFA) profiling. According to PLFA indicators, microbial biodiversity as well as bacterial and fungal abundance dropped sharply with the onset of FCRR in fields planted with the cultivar Guelph Millenium. This drop was followed by a similar drop in the arbuscular mycorrhizal population. Biodiversity and microbial population size then increased to finally reach a new equilibrium. Discriminant analysis of PLFA profiles obtained from soil samples also indicated a shift in soil microbial community structure associated with FCRR development in fields planted with the cultivar Jersey Giant. Different soil biological conditions, as indicated by microbial biomass C and N and soil enzyme activities, were associated with different cultivars. Preceding crop, manure application, geographical location and tillage depth also influenced the structure of soil microbial communities in asparagus plantations, as determined by PLFA profiling. If higher FCRR incidence is a consequence of the soil microbial community reorganization, means to reduce FCRR incidence in asparagus plantations may be found among practices such as soil organic fertilization, soil tillage and intercropping strategies that would dilute the negative influence of asparagus on the soil microbial community. Finally, FCRR outbreaks were generally promoted by a previous crop of maize. It seems that maize and asparagus host a F. proliferatum teleomorph (Gibberella fujikoroi) of the same mating type.

Airborne fungal ecological niche determination as one of the possibilities for indirect mycotoxin risk assessment in indoor air

Based on the microbiological analysis of air samples from occupied spaces, some possibilities for indirect risk assessment of mycotoxin‐related health problems are proposed. Airborne fungi could be classified on the basis of the relationship between the two environmental factors and their combinations, i.e., temperature and water requirements (water activity aw). One type involves three different groups of molds, selected on the basis of the quantitative and qualitative information about the ability of fungi to sporulate under different environmental conditions: group (i), represented by Aspergillus nidulans, A. niger, and A. ochraceus, and characterized by sporulation which was more dependent on temperature than on water activity; (ii), represented by A. flavus and A. versicolor, in which sporulation was approximately equal and depended on both the temperature changes and aW alterations; and (iii), represented by Cladosporium sp., Penicillium cyclopium, and P. citrinum, in which sporulation depended more on alteration of the aw conditions than on temperature changes. Another type is characterized by four sporulation rates with two levels of mycotoxin risk accumulation in the spores (conidia) of each mold species: large (Ia) and moderate (Ib) sporulation rates with a risk of mycotoxin accumulation (aw≥86; t≥12°C); rare sporulation (IIa) and absence of sporulation (IIb), without risk of mycotoxin accumulation (aw≤86; t≤12°C). In conclusion, providing a useful guide for two dimensions, temperature and water activity for each of the three phases of fungal growth, i.e. germination, growth, and sporulation, could be important for determination of the fundamental niche of each fungus and its ability to form or accumulate mycotoxin. Special emphasis should be given to the indirect mycotoxin risk assessment in heating, ventilation, and air conditioning systems.u2003© 2001 John Wiley & Sons, Inc.u2003Environ Toxicol 16: 1–8, 2001

Changes in Communities of Fusarium and Arbuscular Mycorrhizal Fungi as Related to Different Asparagus Cultural Factors

Asparagus (Asparagus officinalis) is a high-value perennial vegetable crop that has shown a marked decline in productivity after many years of continuous harvesting. This decline is caused by an increase in both abiotic (autotoxicity, harvesting pressure) and biotic stresses [fungal infections, mainly Fusarium crown and root rot (FCRR)]. To gain insight into disease development and possible mitigation strategies, we studied the effects of harvesting, time in the growing season, and field age on FCRR development, Fusarium species composition, and arbuscular mycorrhizal fungi (AMF) communities in both a controlled field experiment and an ecological survey of commercial fields. In one experiment, a 3-year-old asparagus field was subdivided into plots that were harvested or not and sampled throughout the growing season to assess short-term dominant Fusarium species shifts. In addition, diseased and healthy asparagus plants sampled from six commercial fields in the same geographical region were used to assess Fusarium and AMF communities in relation to different parameters. Fusarium and AMF communities were described by using a polymerase chain reaction (PCR)–denaturing gradient gel electrophoresis (DGGE) approach, and results were analyzed by mainly correspondence analysis and canonical correspondence analysis. Results showed that dominant Fusarium taxa assemblages changed throughout the growing season. Harvested plots had significantly more FCRR symptomatic plants at the end of the growing season, but this effect was not related with any trend in Fusarium community structure. Sampling site and plant age significantly influenced AMF community structure, whereas only sampling site consistently influenced the Fusarium community. Diseased and healthy plants harbored similar Fusarium and AMF communities. Shifts in Fusarium community might not be responsible for different disease incidence because they are ubiquitous regardless of plant health status or harvesting regime. The different incidence noted might rather be related to plant physiology, antagonist microbial communities, or soil parameters.

A comparative study of endophytic mycobiota in leaves of Acer saccharum in eastern North America

Endophytic fungal flora of the symptomless lamina and petiole of Acer saccharum have been compared to detect inter-sites and tissue-specific differences in the communities from two native and one urban stands. Twenty seven different fungal taxa were isolated, but only 19 endophytes were present in frequencies of colonization higher than 1 %. Although the species composition overlaps within sites, all of these species were found in an old-growth forest (300 years old), but only 18 (67 %) in a regenerated (managed) forest (80 year old) and 8 (30 %) in an urban plantation. Both, the numbers of species and fungal isolation frequency, were significantly higher for leaves than for petioles, showing an organ and segment-specific distribution. The gradually increasing of the presence of dark mycelia from native forests to urban plantation was discussed on the basis of the presumably impacts of the temperature and light following the 1998 ice-storm in Quebec, Canada.

Patterns of Fusarium community structure and abundance in relation to spatial, abiotic and biotic factors in soil

Members of the Fusarium genus are important components of many plant-soil systems worldwide and are responsible for many crop diseases. Knowledge of the relative influence of biotic and abiotic factors on this genus is therefore of broad economic and ecological importance. In order to address this issue, we examined Fusarium communities in soils nearby apparently healthy and symptomatic asparagus plants in 50 fields scattered in four agricultural regions of Québec, Canada. Fusarium community structure and abundance were assessed using genus-specific PCR-denaturing gradient gel electrophoresis and CFU counts, respectively. Multivariate statistical analyses were used to detect community patterns related to spatial, abiotic and biotic factors. Results suggested that Fusarium community structure (i.e. the presence and absence of the different Fusarium sequence variants in the samples) in soil is mainly related to biotic factors (arbuscular mycorrhizal fungi and bacterial community structure), whereas Fusarium abundance is more closely related to abiotic factors (mainly clay, organic matter, NH(4), Na and Cu). Some degree of influence of spatial patterns was also observed on both Fusarium community structure and abundance with, for instance, a large regional variation in Fusarium community structure. However, Fusarium community structure was not directly related to the disease status of nearby asparagus plants.

Phialocephala victorinii sp. nov., endophyte of Cypripedium parviflorum.

A new hyphomycete Phialocephala victori- nii sp. nov. is an endophyte isolated from living roots of the terrestrial orchid Cypripedium parviflorum. Phialocephala victorinii is typical of the genus in mor- phology and ecology, but clearly different from other known species of Phialocephala in having characters not previously described: slow growing colony, dark brown to golden brown on malt agar, and sporulating readily on corn meal agar, bearing regular conidio- phores, sterile lateral protuberances present on hy- phae in fertile region and not on the conidiophores, stipe base and apex subhyaline, collarettes extremely expanded, and conidia of two kinds: dark brown, ob- ovoid or lunate, and light brown, allantoid conidia. Its sensitivity to cycloheximide suggests an affinity in- side Phialocephala and no teleomorph connection with Ophiostoma. The taxonomic placement of the new species and a key to the members of Phialoce- phala are given.

Leptomelanconium abietis sp. nov. on needles of Abies balsamea

A new species of Coelomycete, Leptomelan- conium abietis, is described and illustrated from chlo- rotic and necrotic needles of Abies balsamea. This

New hosts for Choanatiara lunata

Choanatiara lunata is a coelomycetous fungus producing conidia with funnel-shaped appendages. The species was originally reported on fallen needles of Pinus resinosa and P. strobus in Ontario, Canada. Our systematic work on coelomycetes in Pinus spp. was carried out on 29 different pine hosts (species, varieties, forms or cultivars) at the arboretum of the Montreal Botanical Garden. Choanatiara lunata was isolated (on PDA, MA, CMA) from 9 (31%) of the pine hosts investigated. From those, four hosts are species indigenous to North America: P. albicaulis (subgenus Haploxylon), P. resinosa, P. ponderosa, and P. jeffreyi (subgenus Diploxylon). The other five hosts are pines exotic to North America. Three are indigenous to Europe: P. nigra ‘Laricio’, P. nigra ‘Nigra’, and P. nigra ‘Pallasiana’ (subgenus Diploxylon), and two are indigenous to East Asia: P. densiflora and P. tabulaeformis (subgenus Diploxylon). Except for P. resinosa, these are all new hosts for this fungus. The fungus was associated with sympto...