Infection of Picea abies clones with a homokaryotic isolate of Heterobasidion parviporum under field conditions

Abstract

Heterobasidion parviporum Niemelä & Korhonen is responsible for the majority of decay in conifers in northern Europe, which causes severe economic losses. In nature, heterokaryotic isolates of H. parviporum cause infection in Norway spruce (Picea abies (L.) Karst.). However, little is known on whether homokaryons of H. parviporum can infect trees under field conditions. In this study, 40-year-old clonal Norway spruce stems and roots were inoculated with a homokaryotic isolate of H. parviporum under field conditions. After four months, the infection frequency and necrotic lesion lengths were recorded. The homokaryon caused infection and provoked the development of necrotic lesions. Necrotic lesions were larger in roots than in stems. Among the studied Norway spruce genotypes, a Russian clone had the smallest necrotic lesions, whereas a Finnish clone developed the largest necrotic lesions. Clones with higher growth rates were more sensitive to fungal infection and wound damage. Under microscopic observation, H. parviporum grew adpressed to lumen cell walls, colonized tracheids next to rays, and induced lignification in cell walls close to the point of inoculation. This study provides a starting point for further studies on the ability of homokaryons to cause infection under field conditions and for discussions on factors affecting the resistance of Norway spruce against H. parviporum.Résumé : Chez les conifères d'Europe du Nord, la majeure partie de la carie qui est responsable d'importantes pertes économiques est causée par Heterobasidion parviporum Niemelä & Korhonen. En nature, des isolats hétérocaryotes de H. parviporum infectent l'épicéa commun (Picea abies (L.) Karst.). Cependant, on ne sait pas si des homocaryons de H. parviporum peuvent infecter les arbres sur le terrain. Dans cette étude, les racines et la tige d'individus clonaux d'épicéa commun âgés de 40 ans ont été inoculés avec un isolat homocaryote de H. parviporum sur le terrain. Après quatre mois, la fréquence des infections et la longueur des lésions nécrotiques ont été notées. L'homocaryon a causé une infection et provoqué le développement de lésions nécrotiques. Les lésions nécrotiques étaient plus grandes sur les racines que sur la tige. Parmi les génotypes d'épicéa commun étudiés, un clone russe avait les lésions nécrotiques les plus petites tandis que les plus grandes lésions se retrouvaient sur un clone finlandais. Les clones qui avaient le taux de croissance le plus élevé étaient plus sensibles aux infections fongiques et aux dommages causés par les blessures. Sous observation microscopique, H. parviporum croissait adossé à la paroi cellulaire à l'intérieur des cellules, colonisait les trachéides adjacentes aux rayons et induisait la lignification dans la paroi des cellules situées près du point d'inoculation. Cette étude constitue un point de départ pour d'autres études portant sur la capacité des homocaryons à causer des infections sur le terrain et pour alimenter la discussion concernant les facteurs qui influencent la résistance de l'ép...

Intraspecific comparative genomics of isolates of the Norway spruce pathogen (Heterobasidion parviporum) and identification of its potential virulence factors

“…Inoculation of homokaryotic H. parviporum isolates on Norway spruce seedlings further confirmed that heterokaryosis is not absolutely required for the pathogenicity of H. parviporum homokaryons as previously observed [ 70 , 71 ]. We then examined other phenotypic traits i.e.…”

Evaluation of potential genetic and chemical markers for Scots pine tolerance against Heterobasidion annosum infection

“…Despite the fact that field studies on root disease in natural forest ecosystem require more time than greenhouse studies (Swedjemark and Stenlid 1996), artificial inoculations have been applied successfully in the field experiments to examine tree susceptibility to Heterobasidion infection (Swedjemark and Karlsson 2004;Karlsson et al 2008;Danielsson et al 2011;Keriö et al 2014). Although artificial inoculation followed by sampling of lesion areas is commonly done, relying solely on destructive inoculation to screen for resistant genotypes poses a technical and logistical challenge, which may be impractical for large-scale screening of novel biomarkers for durable resistance.…”

“…The inoculation method used ( Fig. 1) was similar as previously described (Keriö et al 2014;Mukrimin et al 2018). The stem surface was sterilized with 70% ethanol followed by making a hole with a 70% ethanol-sterilized puncher (10-mm diameter) through the tree bark to remove the rhytidome, phellem, and cambium.…”

Genome-Wide Exon-Capture Approach Identifies Genetic Variants of Norway Spruce Genes Associated With Susceptibility to Heterobasidion parviporum Infection

“…However, a combination of biotic and abiotic factors pose a threat to sustainable timber supply from Norway spruce plantations (Lindroth and St. Clair, 2013 ; Oliva et al, 2013 ; Robert et al, 2013 ; Lind et al, 2014 ; Wang et al, 2015 ). Among microbial pathogens of Norway spruce, necrotrophic fungi of the Heterobasidion annosum species complex occupy an outstanding position due to their devastating effect on commercial plantations (Keriö et al, 2014 ). Members of this species complex are causative agents of root and butt rot of conifer trees throughout the boreal and temperate zones of Northern hemisphere (Abu et al, 2004 ; Asiegbu et al, 2005a ; Garbelotto and Gonthier, 2013 ; Gunulf et al, 2013 ; Skrøppa et al, 2015 ).…”