Genome Resources for Thelonectria rubi, the Causal Agent of Nectria Canker of Caneberry

Thelonectria rubi is the causal agent of Nectria canker of Rubus spp. Here, we report a high-quality draft genome sequence for this pathogen, which also represents the first genome sequence for a Thelonectria species. The genome assembly was 44.6 Mb in size, assembled into 669 scaffolds and consisting of 12,973 predicted protein-coding genes. The availability of genome data for T. rubi provides a critical additional resource for an important plant pathogen and will be useful for fungal biology, comparative genomic, taxonomic and population studies of this and related species.

Nectria Canker Incidence on Birch (Betula spp.) in Connecticut

A comparison of Nectria canker (caused by Neonectria ditissima) incidence was made between contemporary stands and data sets collected in the 1930s. Cankers were noted on 2,520 black and 1,704 yellow birch growing in 31 study areas used during seven separate surveys in Connecticutbetween 1995 and 2005. Canker incidence was compared with a survey of 6,938 black and 4,117 yellow birch completed during 1934‐1935. Canker incidence in the mid-1930s was much greater than recent incidence for most diameter, crown, and age classes. Birch that grew in open conditionshad higher canker incidence than understory birch. In unmanaged mature stands, canker incidence in 2000 was higher for birch older than 90 years (24%) than for birch 20‐29 years old (1%) and 30‐49 years old (2%). Because the younger birch are probably progeny of intermingled older birch with cankers, is unlikely that the lower incidence of cankers observed on the younger birch was related to local soil conditions, a genetically resistant population, or lack of inoculum. Incidence in more recent surveys was much higher for 20‐29-year-old (12%) and 30‐49-year-old(32%) birch in clearcuts <50 years old than for birch of similar ages in unmanaged forests. Canker incidence of birch in clearcuts was similar to older birch in mature stands and birch during the mid-1930s (13%) that became established following clearcutting or farm abandonment. Canker incidence in birch might be reduced by regeneration prescriptions that minimize exposure of birch saplings to “open-field” environmental conditions during early stand development and by removing infected stems during the early thinning operations.

PATHOLOGICAL ANATOMY OF NECTRIA CANKER ON FRAXINUS MANDSHURICA VAR. JAPONICA

The anatomical characteristics of Nectria canker on Fraxinus mandshurica var. japonica were analyzed. Typical cankers were conspicuous, round to oval, with uniform concentric rings of affected xylem in a target-like structure. Each concentric annual growth ring was wider than the corresponding annual rings lateral to the cankers. The xylem elements were extremely disoriented. The cambial zone became discontinuous and disappeared. An inoculation test with the causal fungus, Nectria galligena, produced similar anatomical abnormalities and revealed the process of canker formation. Fewer and narrower vessels were formed, and water conduction took place only in the large vessels of the current year in the cankers.