Characterization and Pathogenicity of Botryosphaeriaceae Fungi Associated with Declining Urban Stands of Coast Redwood in California

Abstract

Coast redwood (Sequoia sempervirens) is among the most widely planted landscape trees in California (CA) but is in decline outside its natural range due to factors including prolonged drought and plant pathogens. We investigated associations of Botryosphaeriaceae fungi with declining coast redwood trees throughout CA. More than 100 samples were collected from 11 coastal and inland locations in CA. Fifty-nine Botryosphaeria-like fungal strains were isolated and 18 were selected for further study. Phylogenetic analysis of ITS and EF-1α sequence data confirmed the presence of Botryosphaeria dothidea, Neofusicoccum australe, N. luteum, N. mediterraneum, and N. parvum. Pathogenicity testing showed that although the Neofusicoccum species vary in virulence, all are more virulent that B. dothidea. N. australe caused the largest lesions, followed by N. luteum, N. parvum, and N. mediterraneum. Of the species recovered, only B. dothidea has been previously confirmed as a pathogen of coast redwood in CA. These results confirm that multiple Botryosphaeriaceae species are associated with branch decline and dieback on coast redwood in CA, which agrees with similar studies on woody agricultural crops. Accurate diagnosis of fungal pathogens of coast redwood is important for the development of disease management strategies and may help improve horticultural practices in maintenance of urban stands.

Choosing an Adequate Pesticide Delivery System for Managing Pathogens with Difficult Biologies: Case Studies onDiplodia corticola, Venturia inaequalisandErwinia amylovora

“…However, in support of the true pathogen lifestyle, the inoculation tests with isolated D. corticola strains conducted on young, healthy, naturally established trees of black oak clearly demonstrated the pathogenicity of D. corticola. In a similar case in California, closely related Botryosphaeriaceae fungi Neofusicoccum australe, N. luteum, N. parvum, N. mediterraneum and Botryosphaeria dothidea have been isolated from declining coast redwood trees (Sequoia sempervirens) in the urban stands, which were severely drought stressed [9]. However, the inoculation tests with the isolates of these fungal species on potted healthy young trees of coast redwood clearly showed that Neofusicoccum species were true and very virulent pathogens, while B. dothidea was an opportunistic pathogen that did not cause severe infection on healthy trees [9].…”

“…In a similar case in California, closely related Botryosphaeriaceae fungi Neofusicoccum australe, N. luteum, N. parvum, N. mediterraneum and Botryosphaeria dothidea have been isolated from declining coast redwood trees (Sequoia sempervirens) in the urban stands, which were severely drought stressed [9]. However, the inoculation tests with the isolates of these fungal species on potted healthy young trees of coast redwood clearly showed that Neofusicoccum species were true and very virulent pathogens, while B. dothidea was an opportunistic pathogen that did not cause severe infection on healthy trees [9]. The other members of Botryosphaeriaceae family, such as B. dothidea [23,74,75] or Diplodia sapinea [76], are well-known opportunistic pathogens that dwell on the tree asymptomatically for months or even years, until the plant becomes weakened through any number of abiotic or biotic stresses (e.g.…”

“…Agricultural, urban, and natural tree stands have been the focus of extensive plant pathogen diagnostic and disease management research in recent decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] which recorded an increase in the number of new fungal and bacterial pathogens and their detrimental impact on agroecosystems, ecosystems, and the human society. The economic effects of these pathogens are reflected in lost fresh fruit produce [17][18][19], reduced yields and quality of fruit or wood and cork products [20,21], diminished ecological tree services, and death of whole trees, stands, and forest regions or decimation of fruit industries [19,22].…”

“…Recently, there has been a rising incidence of this pathogen in the Unites States on northern red oak, Q. rubra [5,8], black oak, Q. velutina [7], white oak, Q. alba [28], and bur oak (Q. macrocarpa) [29]. Other Botryosphaeriaceae, like Neofusicoccum australe, N. luteum, N. parvum and N. mediterraneum infect woody and green plant tissues and are destructive canker pathogens of avocado [1], grapevine, olive, pistachio and ash [30][31][32][33] and are recently reported as very virulent pathogens of coast redwood leading to severe decline in urban stands of California [9]. The Blue stain fungi Grosmannia clavigera and Leptographium longiclavatum are the plant pathogenic insect symbionts vectored by the mountain pine beetle Dendroctonus ponderosae [13].…”

First molecular insights into the infection process provoked by Neofusicoccum parvum in Liquidambar styraciflua and the identification of new cysteine-rich proteins in both organisms

“…[7] pomegranate (Punica granatum) [8], peach (Prunus persica) [9] and walnut (Juglans regia) [10]. The forestry host plants include the coast redwood (Sequoia sempervirens) [11], Norfolk Island pine (Araucaria heterophylla) [12], Eucalyptus globulus [13,14], and Ginkgo biloba [15]. It is worth mentioning that most studies have focused basically on the isolation of the fungus from symptomatic or asymptomatic tissue, followed by molecular identi cation and pathogenicity testing through Koch's postulates; however, molecular information has been obtained only for the interaction between grapevine and N. parvum [16][17][18][19].…”