sdu faculty of forestry journal special edition 2009 - Orman Fakültesi

SDU Faculty of Forestry Journal
Serial: A, Number: Special Issue, Year: 2009, ISSN: 1302-7085, Page: 85-92
ADELGID GALLS ON SPRUCE AS A RESERVOIR INOCULUM
SOURCE FOR THE SHOOT BLIGHT PATHOGEN Diplodia pinea
Glen R. STANOSZ 1*, Denise R. SMITH 1 , S. ZHOU 2
1 Department of Plant Pathology and 2 Genomics Center of Wisconsin, University of Wisconsin-
Madison, WI, 53706, USA
ABSTRACT
* grs@plantpath.wisc.edu
Diplodia pinea is a shoot blight and canker pathogen of many conifers and sporulates
on killed needles, stems, and mature, opened seed cones. Although Colorado blue spruce
(Picea pungens) is an atypical host, pycnidia of this fungus were observed on galls induced
by the Cooley spruce gall adelgid (Adelges cooleyi). The elongate, cone-like galls that
form on ends of shoots as a result of feeding by nymphs of this insect normally do not
seriously impact tree health, but they can be considered unsightly. A survey was conducted
to determine the incidence and abundance of inoculum of D. pinea that could be obtained
from these galls on an otherwise healthy, ornamental Colorado blue spruce in Madison, WI,
USA. Ten arbitrarily selected galls were collected from one branch at each of four
directions in the top, middle, and bottom thirds of the tree crown (120 galls total). A
washing and filtration technique was used to determine presence and estimate the numbers
of conidia extracted from these galls, and species-specific PCR primers were used to
confirm the identity of the pathogen. Conidia were obtained from each gall, but the number
of spores varied greatly from gall to gall. Some galls yielded few spores, a result that
suggests these conidia may have been produced elsewhere. In contrast, many thousands of
spores were obtained from galls on which pycnidia were abundant. Thus, in the absence of
usual host trees, insect-altered organs of an atypical host can be an alternative substrate for
this pathogen and a reservoir inoculum source of D. pinea.
Keywords: spruce, Picea, gall, Adelges, Diplodia, inoculum
1. INTRODUCTION
Elongate, cone-like galls form on ends of shoots of several Picea A. Dietr.
species as a result of feeding by nymphs of the Cooley spruce gall adelgid (Adelges
cooleyi Gillette) (Cumming, 1959; USDA Forest Service, 1985). This insect is
native to North America and transcontinental in distribution. Primary hosts include
Colorado blue spruce (P. pungens Engelm.), Englemann spruce (P. englemannii
Parry ex Englem.), Sitka spruce (P. sitchensis (Bong.) Carrière), and white spruce
(P. glauca (Moench) Voss. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is
an alternate host. Similar galls are induced by the eastern spruce gall adelgid
(Adelges abietis L.), which was introduced from Europe and is now found in
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