Treesearch

Elm susceptibility to Dutch elm disease (DED) displays strong seasonal variation. The period during which elms can become infected and express DED symptoms is generally restricted to several weeks after growth resumption in spring, although it can vary among species, provenances, and environmental conditions. The reason for this phenomenon is not understood, but the few studies correlating DED susceptibility with the host’s rhythm of seasonal morphogenesis suggest that the seasonal variation in disease development depends on the pattern of growth. Susceptibility to DED is correlated to the...

The oomycete Phytophthora ramorum is a plant pathogen with an unusually broad host range. Recognized in 2000 as a previously unknown and likely introduced species, this pathogen has become established in central and northern coastal California, southwestern Oregon, and Western Europe. Tree species that may be killed by stem cankers include true oaks (Quercus agrifolia Née, Q. kelloggii Newb., Q. parvula var. shrevei (C.H. Muller) Nixon, and Q. chrysolepis Liebm.), and tanoaks (Notholithocarpus densiflorus Hook. and Arn.), in North America; and Japanese larch (Larix kaempferi (Lam.)...

Summary The first wildfires in sudden oak death-impacted forests occurred in 2008 in the Big Sur region of California, creating the rare opportunity to study the interaction between an invasive forest pathogen and a historically recurring disturbance. To determine whether and how the sudden oak death pathogen, Phytophthora ramorum, survived the wildfires, we completed intensive vegetation-based surveys in forest plots that were known to be infested before the wildfires. Wethen used 24 plot-based variables as predictors of P. ramorum The likelihood of recovering P. ramorum from burned plots...

Constitutive chemical defenses, always expressed in the plants, and plastic defensive responses, those mobilized in response to plant injury or other cues or herbivory risk, differ in their benefits in terms of fitness for long-lived plants. Induced defenses are considered to be less expensive than constitutive preformed defenses since the cost is realized only when required. Plant defense theory predicts that, as secondary metabolism is costly for the plant, presenting effective levels of constitutive defenses and the ability of expressing efficient inducible defenses by a plant are two...

In North America, hemlock woolly adelgid (HWA; Adelges tsugae) is an exotic insect pest from Asia that is causing rapid decline of native eastern hemlock (Tsuga canadensis (L.) Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.) populations. The exact physiological mechanisms that cause tree decline and mortality are not known, despite substantial research efforts on ecological impacts and potential control measures of HWA. Eastern and Carolina hemlock may be reacting to infestation in a manner similar to the response of Fraser fir (Abies fraseri (Pursh.) Poir.) to infestation by...

The elm breeding program carried out in Italy at the Institute of Plant Protection - Consiglio Nazionale delle Ricercje (CNR) during the last 40 years aimed to develop Dutch elm disease (DED)-resistant elm selections specific to the Mediterranean environment. The need for genotypes adapted to Mediterranean conditions was evident from the poor performance of the Dutch elm clones in the hot and dry areas of central Italy, and the opportunity to breed better adapted hybrids was offered by the favorable adaptation in Italy of the Siberian elm (Ulmus pumila L.), a species that does not thrive...

Routine selection is simply defined as “the ecological constraints experienced by an endemic organism that favor a relatively stable but fluctuating population structure over time.” Its antithesis is episodic selection, defined as “any sudden ecological disturbance likely to lead to a significant alteration in a species’ population structure” (Brasier 1986, 1995). In plant pathogens, examples of episodic selection are common in the context of modern anthropogenically driven disturbance conditions such as sudden exposure to crop monoculture or to a new fungicide, host, or vector; or sudden...

Plant ecologists have debated the mechanisms used by plants to cope with the impact of herbivore damage for more than a century. During that time, plant resistance mechanisms, which reduce the amount of herbivore damage before and during herbivory, have received most of the attention, while plant tolerance mechanisms, which may minimize the impacts of damage after herbivory, have been less studied. The aim of this presentation is to bring the topic of plant compensatory responses, especially compensatory growth, to the front of research in plant ecology and plant-herbivore interactions. We...

Since the early 1980s, an epidemic forest disease, Japanese Oak Wilt (JOW), has been spreading from coastal areas along the Sea of Japan to the interior of Honshu island and has been devastating huge areas of forests by killing an enormous number of oak trees in urban fringe mountains, gardens, and parks. The disease is caused by a fungus, Raffaelea quercivora, and is spread by the vector beetle, Platypus quercivorus (Coleoptera: Platypodidae). On the thorax of female P. quercivorus, are several holes, so called mycangia, where several species of yeasts are kept as the beetles’ food....