Cadophora spp.: Plant pathogens, colonizers of trunks and roots, and saprophytes of the wood - Culture; Molecular diagnosis (PCR and sequencing).

 

Information 14-10-2018.

Filamentous fungi of the genus Cadophora are found in many habitats, being isolated mainly from soil and plants, either interacting as pathogens, colonizers of roots or trunks, or saprophytes. Originally known as the cause of the blue stain of wood, Cadophora species have received little attention in the past. However, recent studies place different species of the genus as possible pathogens of the vines and other plants in different countries, and consequently interest and research around this genus has increased considerably.

Cadophora genus was established in 1927 by Lagerberg and Melin, with Cadophora fastigiata as the type species, to include dematiaceous hyphomycete fungi that produce conidiophores of a single phialide with distinctive bottle-shaped collaretes ranging from pale to hyaline, and with vegetative hyphae more or less pigmented. In 1937, Conant transferred eight species of Cadophora to the genus Phialophora, based on similarities of the phialides morphology with the polymorphic species Phialophora verrucosa. However, the reclassification of the Phialophora-like anamorph or imperfect fungi and the subsequent analysis of ribosomal DNA, showed that members of the genus Cadophora belong to the order Helotiales (Leotiomycetes), and differs from the genus Phialophora, which belong to the order Chaetothryales (Eurotiomycetes).

Interest in Cadophora spp. came initially from its frequent association with the blue stain of the wood. However, currently, the known species of the Cadophora genus are classified into the following groups: tree and grape pathogens, endophytic fungi associated with roots and saprophytic species. In many cases, the role of these species as plant pathogens is not completely known. As we advance in the knowledge of the role of these species as pathogens of legumes, the kiwi fruit trees, the grapevines, and different hardwood trees, we also discover new species within this genus.

Among the pathogens, Cadophora gregata is a soil-borne vascular pathogen that causes brown stem rot of the soybean, a disease that has a significant economic impact on the soybean industry in the United States. Also, this species causes the brown stem rot of adzuki sweet beans, a major disease in Japan. C. malorum causes the wood decay of the kiwi fruit. Two other species, C. melinii and C. luteo-olivacea, have also been isolated from the wood of kiwi fruit trees that presented trunk hypertrophy and longitudinal cracks in the bark. C. novieboraci, C. orientoamericana and C. spadicis have been suggested as grapevine trunk pathogens in North America. Meanwhile, C. luteo-olivacea and C. viticola (previously erroneously identified as C. melinii) have been isolated from asymptomatic and symptomatic grapevine woods in different regions of the world, including Spain. It is believed that C. luteo-olivacea is associated with the trunk diseases Esca and, in young vineyards, Petri disease. In addition, recently, a new species Cadophora margaritata has been described, which together with C. spadicis, has been associated with the degradation of hardwood trees colonized by beetles.

The species C. malorum, C. finlandica, C. interclivum and C. meredithiae are considered colonizers of roots and are included among the so-called "dark septate endophyte" fungi (DSEs, for its acronym in English). The DSEs produce partially or totally melanized and septated hyphae and live asymptomatically in the roots of the vascular plants, being common in the arctic and alpine areas. It is believed that they play a quasi-chemical role, since they do not seem to have adverse effects on plant health, and on the contrary, some DSEs such as C. filandia increase phosphorus and nitrogen concentrations in leaves.

Finally, C. malorum, C. luteo-olivacea and C. fastigiata have been isolated from soil and deteriorated wood in extreme environments, such as Antarctica and the Canadian High Arctic, acting as saprophytic microorganisms causing, for example, decay of the wooden huts in Antarctica. Recently, Cadophora antartica, a psychrophilic microorganism recovered from a sample of soil contaminated with diesel in Antarctica, and closely related to C. luteo-olivacea, has been proposed as a new species. Among them, Cadophora fastigiata, the type species of the genus, is also found in the soil, decaying wood and some cereals and grass seeds in several regions, including Europe, North America and the Antipodes. It is associated with very moist wood and has been isolated from the wooden boards of a sauna, from wood pulp and slime from paper mills and from water from humidifiers. In fact, a strain of this species is recommended by the American Type Culture Collection (ATCC) for use in the evaluation tests of chemical preservatives of wood according to the American standard ASTM D4445-91.

Although Cadophora species can be included in different microorganism groups, it is believed that under certain conditions these fungi can change from endophytes or saprophytes to pathogens due to environmental changes. This hypothesis is supported by studies that indicate the presence of C. fastigiata, C. luteo-olivacea and C. malorum as saprophytes in wooden structures in extreme environments, while other studies report that C. luteo-olivacea is pathogenic on grapevines in different regions of the world, such as Spain. This theory has been supported by enzymatic tests, which reflect that both C. luteo-olivacea and C. malorum are able of degrading a wide range of carbon sources releasing soluble phosphorus, suggesting that their trophic modes could vary from active decomposer to plant pathogen depending on its need to exploit nutrients from various sources.

Tests carried out in IVAMI:

  • Isolation in culture and presumptive identification by microscopic examination.
  • Isolation in culture and identification by molecular methods (PCR and sequencing).

Recommended sample:

  • Sample of soil, water, damaged or decaying wood, colonized roots or any substrate in which it is desired to determine the presence of these fungi.

Conservation and shipment of the sample:

  • Refrigerated (preferred): less than 2 days.
  • Frozen: more than 2 days.

Delivery of results:

  • Isolation in culture and presumptive identification by microscopic examination: 7 days.
  • Isolation in culture and identification by molecular methods (PCR and sequencing): 9 days.

Cost of the test:

  • Isolation in culture and presumptive identification by microscopic examination: Consult ivami@ivami.com.
  • Isolation in culture and identification by molecular methods (PCR and sequencing): Consult ivami@ivami.com.