Summary• The role of water stress in the initiation of collar rot by Sphaeropsis sapinea in asymptomatically colonized Pinus resinosa seedlings is reported.• Mortality and frequency of identification of the pathogen was quantified for seedlings subjected to different water regimes or watering regime -fungicide (benomyl) combinations in glasshouse experiments.• In experiment 1, seedling mortality ranged from 8% of repeatedly watered seedlings to 50% of those in the driest regime; data analysis indicated a high probability that mortality was not independent of watering regime. Seedlings developed symptoms resembling those of Sphaeropsis collar rot, and S. sapinea was identified from living (42%) and dead (92%) seedlings. In experiment 2, mortality of repeatedly watered seedlings was low, irrespective of fungicide application. For nonwatered seedlings, however, mortality was greater among seedlings not treated with fungicide (61%) than among benomyl-treated seedlings (37%); data analysis indicated a high probability that mortality was not independent of fungicide treatment.• Sphaeropsis sapinea can act as a latent pathogen; physiological alteration, through water stress, can effect release from the quiescent condition to result in rapid disease development .

Using Populus feedstocks for biofuels, bioenergy, and bioproducts is becoming economically feasible as global fossil fuel prices increase. Maximizing Populus biomass production across regional landscapes largely depends on understanding genotype × environment interactions, given broad genetic variation at strategic (genomic group) and operational (clone) levels. A regional network of Populus field tests was established in the Midwest USA in 1995 to assess relative productivity of 187 clones grown at Westport, Minnesota (45.7°N, 95.2°W); Waseca, Minnesota (only 2000; 44.1°N, 93.5°W); Arlington, Wisconsin (43.3°N, 89.4°W); andAmes, Iowa (42.0°N, 93.6°W). We evaluated biomass potential throughout plantation development and identified clones with yield substantially greater than commercial controls (Eugenei, NM6). For each site, biomass ranges (Mg ha −1 year −1 ) of the best six clones were:

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We present results from a Populus Regional Testing Program that has been conducted in Minnesota, Iowa, Wisconsin, and Michigan over the past six years. Our objectives have been to: 1) identify highly productive, disease resistant intra-and inter-specific clonal selections and 2) understand patterns of genotype x environment interactions within the region that would, logically, govern commercial deployment of new clones. Clones were developed by breeding and selection programs at the University of Illinois, Iowa State University, University of Minnesota, and the USDA Forest Service for experiments established in 1995. We report results of analyses of variance and principal component analyses of tree diameters and estimated above-ground biomass that demonstrate significant genotype main effects and significant genotype x environment interactions. Maximum mean annual above-ground biomass increments have surpassed 16 Mg ha-' y-', exceeding previously reported yields of poplars grown under similar conditions in the north-central U.S. We also discuss the breeding and selection of poplars in general with specific attention to regional research needs.

A polymerase chain reaction (PCR)-based assay was developed for the specific detection of the fungal pathogens Diplodia pinea and D. scrobiculata from pine host tissues. Variation among mitochondrial small subunit ribosome gene (mt SSU rDNA) sequences of Botryosphaeria species and related anamorphic fungi was exploited to design primer pairs. Forward primer DpF and forward primer DsF, each when used with the nonspecific reverse primer BotR, amplified DNA of D. pinea or D. scrobiculata, respectively. Specificity was confirmed using multiple isolates of each of these two species and those of closely related fungi including Botryosphaeria obtusa. The detection limits for DNA of each pathogen in red and jack pine bark were 50 to 100 pg μl-1 and 1 pg μl-1 in red and jack pine wood. The assay was tested using naturally occurring red and jack pine seedlings and saplings exhibiting symptoms of Diplodia collar rot. Samples from lower stems/root collars of 10 dead trees of each species from each of three sites at each of two locations were tested. Results were positive for D. pinea or D. scrobiculata for the large majorities of symptomatic bark and wood samples from both locations. For positive samples, however, there were effects of location and host species on detection of D. pinea (more frequent on red pine) and D. scrobiculata (more frequent on jack pine) (P < 0.01 in both cases). These results indicate that these new primers are potentially useful for studies in areas or hosts in which both pathogens may be present.