Detection and verification of quantitative trait loci for resistance to Dothistroma needle blight in Pinus radiata.

Six related radiata pine ( Pinus radiata) full-sib families were used to detect and independently verify quantitative trait loci (QTLs) for resistance to Dothistroma needle blight, caused by Dothistroma septospora. The detection families had from 26 to 30 individuals each, and had either a common maternal (31053) or paternal (31032) parent; one family (cross 4) consisted of progeny from both parents, 31053 x 31032. Approximately 200 additional progeny from cross 4 were clonally replicated and planted at two sites, with at least five to seven ramets of each individual per site. Marker segregation data were collected from a total of 250 RFLP and microsatellite markers, and single factor ANOVAs were conducted separately for each family and marker. A number of putative associations were observed, some across more than one family. Permutation tests were used to confirm expected probabilities of multiple associations based on chance alone. Seven markers representing at least four QTLs for resistance to Dothistroma were identified as being significant in more than one family; one of these was significant at P<0.05 in three families and highly significant at P<0.01 in a fourth. Further confirmation was obtained by testing those markers that were significant in more than one of the detection families (or highly significant in cross 4) in the clonally replicated progeny from cross 4. Four QTL positions were verified in the clonal populations, with a total percent variation accounted for of 12.5.

Ceratocystis pirilliformis, a new species from Eucalyptus nitens in Australia.

Several species of Ceratocystis have been recorded on Eucalyptus. These include C. fimbriata, C. eucalypti, C. moniliformis and C. moniliformopsis. Of these, only C. fimbriata is known as a pathogen; it recently has been found causing serious wilt diseases in Uganda, Congo and Brazil. This study was undertaken to collect Ceratocystis species, including C. eucalypti, from artificially induced wounds on Eucalyptus nitens near Canberra in southeastern Australia. Trees were wounded in October 2000, and wounds were examined approximately one month later. Ascomata characteristic of a Ceratocystis species were found covering the wounds, and this fungus also was isolated from the wood using carrot baiting. This species of Ceratocystis has hat-shaped ascospores similar to those of C. fimbriata, but it differs from C. fimbriata and all other species of Ceratocystis in that it possesses ascomata with a pyriform base. Comparison of DNA sequences from the ITS and 5.8S rRNA operon confirmed that the fungus from E. nitens in Australia is unique, and we describe it here as a new species, C. pirilliformis.

Climatic mapping to identify high-risk areas for Cylindrocladium quinqueseptatum leaf blight on eucalypts in mainland South East Asia and around the world.

Cylindrocladium quinqueseptatum is a pathogen on a wide range of hosts. It affects at least 20 species of eucalypts and is an important causal agent of leaf blight of Eucalyptus camaldulensis in central and southern Vietnam. Results from previous studies and observations of broadscale infection patterns in mainland South East Asia were used to derive simple rules (i.e. mean minimum temperature of coldest month > or =16 degrees C and mean annual precipitation > or =1400 mm) to identify locations which are likely to have a high risk of C. quinqueseptatum leaf blight (CqLB). Climatic mapping programs, which include interpolated climatic data estimated for numerous locations, were used to map these high risk areas in Africa, Australia and Latin America as well as in South East Asia. The predicted high-risk areas included several regions where CqLB has already been reported and the maps generated suggested other areas which may be at risk under present climatic conditions given the presence of C. quinqueseptatum and susceptible hosts. Some simple climate change scenarios were also used to suggest areas in mainland South East Asia which may become vulnerable to CqLB over the next 50 years. It is concluded that climatic mapping programs can assist the broadscale evaluation of risk of CqLB infections, although it is recognised that more detailed models and survey information are also needed.