James J. Worrall

Summer heat and an epidemic of cytospora canker of Alnus

An epidemic of cytospora canker [Valsa melanodiscus, anamorph Cytospora umbrina] is associated with dieback and mortality of Alnus incana ssp. tenuifolia in the Southern Rocky Mountains and had begun by the late 1980s. Isolations showed that inoculum was often abundant on bark and bud surfaces even in winter, especially near diseased stems. The pathogen was occasionally isolated from internal tissues of dormant buds and asymptomatic wood and phloem. In infected stems, the pathogen was detected up to 5 cm beyond visible canker margins. The data suggest that the pathogen can cause latent infections, but the infection court remains unclear. Inoculations of healthy stems in the field did not induce canker formation. Fruiting of the anamorph was primarily in late winter and spring, and sexual maturation occurred in late summer and fall. Stem age and growth data support earlier conclusions that the mortality does not represent a steady-state condition with normal attrition of older stems. Canker expansion and killing of branches and stems occurred almost exclusively in the warmest part of summer. We present a hypothesis and supporting evidence suggesting that warm summer temperatures are conducive to the disease. Locally, summer temperatures, and especially maxima, have varied with a dominant oscillation period of approximately 21 years. We speculate that alder populations expand during cool climate phases and shrink during warm phases due to epidemics of cytospora canker. More recently, the oscillation has dampened as an increasing trend of temperature has become dominant, locally and globally. If the trend continues, this already severe epidemic may become more damaging, without intervening opportunities for alder populations to recover.

Bursaphelenchus masseyi sp. n. (Nematoda: Parasitaphelenchinae) – a nematode associate of the bark beetle, Trypophloeus populi Hopkins (Coleoptera: Curculionidae: Scolytinae), in aspen, Populus tremuloides Michx. affected by sudden aspen decline in Colorado

Bursaphelenchus masseyi sp. n. is described from trunks of unhealthy trembling aspen, Populus tremuloides, affected by sudden aspen decline (SAD) in Colorado, USA. All propagative stages of the nematode were present in larval galleries of a bark beetle, Trypophloeus populi. The dauer juveniles occupy the haemocoel of older larvae, pupae and adult beetles. The characteristic morphology of the male spicules with small but distinct cucullus, extended anterior vulval lip in female, lateral fields with four incisures, and number and arrangement of male caudal papillae, indicate that B. masseyi sp. n. is closely related to the xylophilus group. This relation has been confirmed by DNA sequencing and phylogenetic analysis of the 28S rDNA region. The new species is characterised by the body length of 958 (765-1203) μm in female and 874 (691-1122) μm in male, moderately slender body (a = 38.2 (33.5-41.1) and 38.0 (33.1-44.1) in female and male, respectively), and spicules 29.2 (26.2-34.7) μm long with a small cucullus (1.3-1.5 μm in diam.) at their tips. Bursaphelenchus masseyi sp. n. can be separated from other species in the xylophilus group by the morphology of spicules which have a short capitulum and unique rostrum that is pointed somewhat anteriorly, relatively thick vulval flap, which is straight, parallel to the body long axis and bent towards the body wall at its distal end, and other morphological and morphometric characters. The new species most closely resembles B. trypophloei, but differs by the morphology of spicules (short but distinct condylus vs condylus in a continuous line with dorsal lamina, and smaller cucullus). The taxonomic separation of the new species is also confirmed by the unique molecular profile of the ITS region (ITS-RFLP). Diallelic cross-breeding in vitro revealed also that B. masseyi sp. n. and B. trypophloei are reproductively incompatible. The new species showed poor ability to develop and reproduce on Botrytis cinerea cultures, although it grew vigorously on laboratory cultures of Polish and Colorado isolates of Cytospora chrysosperma, the fungus naturally associated with galleries of the nematode vector, T. populi.

Response of Alnus tenuifolia to inoculation with Valsa melanodiscus

Abstract Valsa melanodiscus (anamorph Cytospora umbrina) has been associated with cankers, dieback, and death of alder (Alnus) stems in western North America. To determine the ability of this fungus to induce these symptoms, the responses of thinleaf alder (Alnus tenuifolia) stems to inoculation with V. melanodiscus were studied in field locations in Alaska and on plants in a greenhouse. In the field, woody stems were wounded to expose both inner bark and sapwood and inoculated in early May 2007 or September 2007 by placing a colonized agar plug over the wound. Sunken, elongated cankers that developed on inoculated stems in the field closely resembled those attributed to natural infection of thinleaf alders by V. melanodiscus. In contrast, wounded control stems exhibited strong callus production and wound closure. In the greenhouse, actively growing lateral shoots were inoculated by placing a colonized agar plug over a fresh leaf scar. Inoculation in the greenhouse resulted in development of cankers, and severity of symptoms was affected by the maturity of the shoot at the point of inoculation. These results support the conclusion that V. melanodiscus is a cause of alder dieback in western North America.

Heterobasidion annosum and H. parviporum in the southern Rocky Mountains and adjoining states.

Collections of Heterobasidion spp. from Nebraska, Colorado, Arizona, and New Mexico were identified based on the sequence of the internal transcribed spacer region of the ribosomal DNA. The North American variant of Heterobasidion annosum sensu stricto was found on Pinus ponderosa and Juniperus virginiana in central Nebraska, southern Colorado, central Arizona, and southern New Mexico. The North American variant of H. parviporum was found on Abies concolor and Picea engelmannii in southern Colorado and central New Mexico. The pathogens were not found in a survey of conifer forests in Wyoming and the Black Hills of South Dakota. Historical records of annosus root disease are reviewed by host group to gain more insight into the potential distributions of the respective pathogens. An apparent lack of overlap in host range suggests that substitution of tree species may be a useful management approach in some cases.