Academic literature on the topic 'Armillaria root rot southern hemisphere'

Armillarioids, including the genera Armillaria, Desarmillaria and Guyanagaster, represent white-rot specific fungal saprotrophs with soilborne pathogenic potentials on woody hosts. They propagate in the soil by root-like rhizomorphs, connecting between susceptible root sections of their hosts, and often forming extended colonies in native forests. Pathogenic abilities of Armillaria and Desarmillaria genets can readily manifest in compromised hosts, or hosts with full vigour can be invaded by virulent mycelia when exposed to a larger number of newly formed genets. Armillaria root rot-related symptoms are indicators of ecological imbalances in native forests and plantations at the rhizosphere levels, often related to abiotic environmental threats, and most likely unfavourable changes in the microbiome compositions in the interactive zone of the roots. The less-studied biotic impacts that contribute to armillarioid host infection include fungi and insects, as well as forest conditions. On the other hand, negative biotic impactors, like bacterial communities, antagonistic fungi, nematodes and plant-derived substances may find applications in the environment-friendly, biological control of armillarioid root diseases, which can be used instead of, or in combination with the classical, but frequently problematic silvicultural and chemical control measures.

Armillaria root rot. caused most likely by Armillaria obscura (Pers) Herink, killed 6-to 21-year-old white spruce, black spruce, jack pine and red pine saplings in each of 49 plantations examined in northern Ontario. Annual mortality in the four species over the last 2 to 6 years averaged 1.4%, 1.5%, 0.5% and 0.2%, respectively. In all but one of 25 white spruce and red pine plantations (43 to 58 years old) in eastern and southern Ontario. Armillaria root rot was associated with mortality. Accumulated mortality in white spruce and red pine (initially recorded in 1978) averaged 7.6% and 11.7%, respectively, as of 1986. Current annual mortality for all plantations ranged from 0% to 16%. Key words: root rot. Armillaria obscura, white spruce, black spruce, jack pine, red pine.

Root rot infections in Norway spruce (Picea abies (L.) Karst.) regeneration, planted after the clear-cutting of spruce on sites infested by Heterobasidion, were investigated on 21 experimental plots in eight 2- to 23-year-old plantations. Heterobasidion root rot became evident about 10 years after planting and the proportion of infected spruces increased steadily with plantation age. The average number of planted spruces infected per old decayed stump was 0.2 trees in 2- to 9-year-old plantations, 0.8 trees in 11- to 15-year-old plantations, and 1.8 trees in 20- to 23-year-old plantations. About 10 and 20 years after planting, 7 and 23% of the planted spruces in the disease centers were infected by Heterobasidion. Heterobasidion parviporum Niemelä & Korhonen, and Heterobasidion annosum (Fr.) Bref. s. str. caused 98 and 2% of the Heterobasidion infections in the previous spruce rotation, and 96 and 4% in the spruce regeneration, respectively. In all, 71% of the infected regeneration trees were attacked by a Heterobasidion genet that was also isolated from the stumps of the previous tree stand. Armillaria species (Armillaria borealis Marxmüller & Korhonen and Armillaria cepistipes Velenovský) were isolated from 7% of the planted spruces.

This study was conducted to assess causes of unprecedented rates of mortality in maturing, commercial-sized red pine(Pinus resinosa Ait.) plantations in southern Ontario, Canada. Concentrated and diffuse mortality as well as windthrowof living trees were observed in many plantations, while others seemed disease-free. Nine sites exhibiting recent mortality(diseased) plus three not exhibiting disease (healthy) were selected. In sample plots at each site, abiotic site factors, hostcharacteristics, and insect pests and fungal pathogens were assessed. Tree mortality was attributed to Armillaria root disease,annosus root rot, black pineleaf scale, drought, and iron deficiency. The single abiotic factor that distinguishedhealthy sites from diseased sites was C soil horizon pH, which averaged 8.35 on diseased sites compared to 6.55 on healthysites. Rooting was also deeper on healthy sites than on diseased sites. We suggest that an alkaline C horizon may result inshallower rooting and greater susceptibility to drought stress, rendering trees less resistant to root disease pathogens andinsect pests. The pH of the C horizon and the depth of the A and B horizons may be useful as indicators of the likelihoodof red pine mortality and to guide the choice of management objectives for plantations. Key words: red pine mortality, root disease, calcareous soil, rooting depth, Armillaria

The development of wood decay caused by 12 major root-rot and trunk-rot fungi was investigated in vitro with sapwood extracted from nine ornamental and landscape hardwood and conifer species native to southern temperate regions of North America, Europe, and the lower Mississippi Delta. Wood decay rates based on dry weight loss for 108 host tree–wood decay fungi combinations were compared at 21 °C over 1-year and 2-year incubation periods in the absence of tree-resistance mechanisms. Strains of Armillaria mellea, Ganoderma lucidum, and Heterobasidion annosum exhibited the highest decay potential in most tree species tested. The order of fungi causing the greatest decay varied over time as a result of temporal changes in decay-rate curves. Relative wood durability or resistance to decay generally was greater in gymnosperm than in angiosperm wood types. Quercus nuttallii, Fraxinus pennsylvanica, and Quercus lyrata sustained the highest levels of decay by all fungi. Northern white cedar (Thuja occidentalis) sapwood was most resistant to decay by all rot-fungi tested, sustaining only limited weight loss after 1 and 2 years of decay, although sapwood of Pinus taeda, Liquidambar styraciflua, and Platanus occidentalis had relatively low levels of decay after 2 years. These results in combination with data from portable decay-detection devices provide useful information for the management of tree breakages or failures resulting from wood decay fungi in hazardous landscape trees. Some potential landscaping applications for tree evaluations, risk assessments, and selections for tree-replacement plantings are discussed.

Ghana is on the verge of exhausting its timber resources and has embarked on reforestation. However, the establishment of pure stands of high value indigenous tree species such as Odum (Milicia excelsa and M. regia), Mahogany (Khaya and Entandrophragma species) and Kokrodua (Pericopsis elata) were not successful as a result of insect pest and disease problems. These failures, together with the need to establish plantations partly account for the widespread planting of teak (Tectona grandis), cedrela (Cedrela odorata) and other introduced tree species. Disease outbreaks in Tectona grandis, Cedrela odorata and Ceiba pentandra have been observed with the expansion of plantation estates. A study was therefore conducted to identify key diseases occurring in tree plantations, determine their distribution and evaluate management strategies to contain them. Diseases encountered include root rot caused by Armillaria hemii on T. grandis and Cedrela odorata, leaf spot and dieback on Ceiba pentandra seedlings and saplings caused by Colletotrichum capsici, Fusarium solani and Lasiodiplodia theobromae, stem canker on Eucalyptus spp. caused by Botryosphaeria sp. and leaf blight caused by a Calonectria species. Management of these diseases will require training of foresters on tree health issues, quarantine and silvicultural practices and initiation of sound breeding and selection programmes.

We report on the 440-year dendrochronological history of a relict, bog forest in the Ridge and Valley Province of central Pennsylvania that contains extreme southern, disjunct populations of Picea mariana (Mill.) BSP and Abies balsamea (L.) Mill. The forest is dominated by Tsuga canadensis (L.) Carr. (49% relative importance value), Picea mariana (16%), and Acer rubrum L. (15%). The few remaining Abies balsamea trees are in a advanced state of decline. Many Nyssa sylvatica Marsh. and T. canadensis trees recruited from 1560 and 1700, respectively, until 1890. However, the majority of the other tree species recruited during a 40-year period following selective logging of the forest in the 1890s and fires in about 1900 and 1914. We found a scarcity of tree saplings and no evidence of recruitment into the tree-size class for any species after 1950. The master tree-ring chronology for both N. sylvatica and T. canadensis exhibits a marked increase after the 1890s logging and a decrease after a 1900 fire. In addition, a large number of releases in individual tree chronologies occurred over the last 400 years, indicating the frequent occurrence of small-scale disturbances. Tree-ring growth during the 20th century was reduced by droughts and cool temperatures in the 1920s and in the early to middle 1960s. Abies balsamea cores exhibit a marked growth decline in 1986. Tsuga canadensis growth was very low between 1970 and 1998, despite a generally warm and wet climate during that time. Picea mariana had a dramatic increase in growth during very warm and wet climate between 1995 and 1998. Most Abies balsamea trees have reached their pathological age of 50-85 years and have active Armillaria root rot, insect infestations, and very poorly developed crowns. These symptoms or severe growth declines are not present in Picea mariana. It appears that the 10 000 year history of Abies balsamea presence at Bear Meadows will end soon, with no opportunity to reestablish itself because of the lack of a local seed source. The results of this study suggest that relict tree populations in the eastern United States may be particularly sensitive to direct and indirect anthropogenic impacts and climatic variations, and represent important benchmarks for comparisons with future studies.Key words: tree rings, disturbance, climate, global change, central Pennsylvania.