Natural infection of an herbaceous host byArmillaria: a case study onHemerocallis^†

Abstract

Symptoms of Armillaria root rot were observed on the herbaceous ornamental, Hemerocallis sp. (daylily), in a residential area in Walhalla, South Carolina, which was surrounded by dense, hardwood forest that also contained diseased hosts. Our objectives were to describe a natural occurrence of Armillaria root rot on daylily, a newly discovered host for the pathogen, and to characterize the Armillaria species involved. To characterize the Armillaria species collected from daylily, we used all available methods, including both traditional (sexual compatibility tests, basidiome morphology) and molecular (phylogenetic analyses of rDNA internal transcribed spacer, ITS, and intergenic spacer I, IGS-I) approaches. The presence of rhizomorphs in the topsoil of daylily beds and on the roots of symptomatic daylilies, coupled with our finding of identical ITS1 sequences among isolates originating from each of a rhizomorph, a daylily, and a neighbouring dogwood, suggests that Armillaria rhizomorphs had spread from native hosts to infect the daylilies. Basidiocarp morphology and basidiospore size best matched that documented for A. gallica. However, rDNA sequence analysis and sexual compatibility were not 100% conclusive. Phylogenetic analysis of ITS sequences revealed that the unknown Armillaria isolates were most closely related to A. calvescens and A. gallica. Analysis of IGS-I sequences was even less informative, grouping our isolates with A. cepistipes, A. gallica and A. sinapina. Sexual compatibility (mating) tests revealed that haploid isolates from daylily were compatible with three of the A. gallica tester isolates, but also one of the A. calvescens tester isolates. Our findings suggest a possible southerly distribution and expanded host range for A. gallica, and raise further questions about the Armillaria species concept as it pertains to the two closely related species, A. calvescens and A. gallica. Résumé:Les symptômes du pourridié-agaric ont été observés sur la plante herbacée ornementale Hemerocallis sp. (belle-d'un-jour) dans un quartier résidentiel de Walhalla, en Caroline du Sud, qui était entouré par une forêt dense de feuillus qui comportait également des arbres infectés. Nos objectifs étaient de décrire une occurrence naturelle du pourridié-agaric sur la belle-d'un-jour, un hôte récemment découvert, et de caractériser l'espèce d'Armillaria impliquée dans le processus. Afin de caractériser l'espèce d'Armillaria collectée sur la belle-d'un-jour, nous avons utilisé toutes les méthodes disponibles, y compris les méthodes traditionnelles (les tests de compatibilité sexuelle, la morphologie du basidiome) et moléculaires [les analyses phylogéniques de l'espaceur transcrit interne de l'ADNr (ITS) et de l'espaceur intergénique I (IGS-I)]. La présence de rhizomorphes dans le sol des massifs de belles-d'un-jour et sur les racines des plants affichant les symptômes, associée à notre découverte de séquences ITS1 identiques dans les isolats provenant d'un rhizomorphe, d'une belle-d'un-jour et d'un cornouiller voisin, su...

A faster inoculation assay forArmillariausing herbaceous plants

“…It is a global problem: in Canada, over 200 million hectares of forests are affected by Armillaria root disease (Canadian Forest Service, 2014;Chapman & Schellenberg, 2015;Cruickshank, 2011); Armillaria infections are also reported from forests across Europe and North and South America (Brazee, Marra, & Wick, 2012;Ferguson, Dreisbach, Parks, Filip, & Schmitt, 2003;Heinzelmann, Rigling, & Prospero, 2012;Labbé et al, 2015) as well as commercial orchards and vineyards (Baumgartner, 2004;Elías-Román et al, 2013;Pellegrini, Prodorutti, & Pertot, 2014;Schnabel, Rollins, & Henderson, 2011), and Armillaria root disease is problematic in Africa, Asia, and Australasia (Coetzee, Wingfield, Zhao, Van Coller, & Wingfield, 2015;Hood, Oliva, Kimberley, Arhipova, & Bakys, 2015;Wingfield, Maphosa, Coetzee, Mwenje, & Wingfield, 2009). Ornamental plants, including herbaceous species, are also affected (Blaedow, Baumgartner, Cox, & Schnabel, 2010;Coetzee et al, 2001;Travadon et al, 2012) and in the UK the majority of enquires received by the RHS Advisory Service over the past 19 years regarding plant diseases in UK gardens have been concerning Armillaria (RHS, 2015).…”

“…As Armillaria root rot is generally regarded as a disease of woody species, Armillaria infection of herbaceous hosts has received little attention. Known herbaceous hosts are typically perennials or species that have succulent roots or tubers and have only been reported occasionally in the literature (Blaedow et al, 2010;Grasso, Pane, & Cacciola, 2000;Guillaumin et al, 1993;Raabe, 1962;Robinson-Bax & Fox, 2002;Thormann, Myrholm, & Mallett, 2001). In this work, we attempt to alleviate some of the difficulties associated with the existing inoculation assays by (1) assessing the suitability of various herbaceous species for use as host plants in Armillaria inoculation assays, and (2) determining whether agar can be used as a substitute for woody inocula to expedite inocula preparation time.…”

A Novel Botrytis Species Is Associated with a Newly Emergent Foliar Disease in Cultivated Hemerocallis

“…The lack of resistance amongst hybrid cultivars - with the one study showing only a minority of the cultivars tested exhibiting any resistance to even a single P. hemerocallidis isolate - demonstrated the susceptibility of cultivated varieties that have been bred outside of their native range in the absence of any pressure from this specific pathogen [11]. Other emerging threats to cultivated daylily include the first reports of infection by the Armillaria genus [12], [13]. Both in the West and in China, anthracnose diseases caused by various Colletotrichum species have been identified and a new species of Colletotrichum, C. hemerocallidis , was recently described from infected leaf and scape material in China [14].…”