Identification and pathogenicity of Botryosphaeriaceae species associated with coast live oak (Quercus agrifolia) decline in southern California

Abstract

Symptoms of decline have been observed on dying coast live oak (Quercus agrifolia) trees in areas throughout southern California that are both infested and uninfested by the gold-spotted oak borer (GSOB). The purpose of this study was to identify and assess the pathogenicity of several anamorph species of the Botryosphaeriaceae, including Diplodia corticola, Dothiorella iberica and Diplodia agrifolia sp. nov., that were recovered consistently from symptomatic tissues. Species were identified morphologically and by phylogenetic analyses of the complete sequence of the internal transcribed spacer (ITS) of the rDNA and partial sequences of β-tubulin and elongation factor (EF1-α) genes. Results from morphological assessments and phylogenetic analyses support the erection of a new species closely related to D. mutila, described herein as Diplodia agrifolia sp. nov. Pathogenicity of all species was verified by wound inoculation of 1 y old coast live oak seedlings under controlled conditions. Isolates of D. corticola were the most aggressive tested, and isolates of D. agrifolia were the second most aggressive. Both species caused bleeding symptoms on inoculated seedlings. Seedlings inoculated with D. corticola died within 4 wk, with the pathogen progressing up and down through the xylem in advance of living phloem and moving throughout the taproot in 70% of inoculated seedlings. Colonization and re-isolation was successful for all species. All three fungal species represent newly recorded fungal pathogens of coast live oak in California. Results from the pathogenicity test suggest that these fungi play a role in the decline of coast live oaks throughout southern California.

Endemic and Emerging Pathogens Threatening Cork Oak Trees: Management Options for Conserving a Unique Forest Ecosystem

“…Studies in the last few decades on pathogenic members of the Phytophthora genus and of the Botryosphaeriaceae and Xylariaceae families have partially filled the gap. Moreover, research conducted in different countries in Africa, Europe, and North America has contributed to expanding knowledge about the pathogenicity, epidemiology, biology, invasiveness, and management of some of these pathogens in different oak forests (Dreaden et al 2014a;Kostovcik et al 2015;Linaldeddu et al 2013;Lynch et al 2013;MoralesRodríguez et al 2016;Moreira and Martins 2005;Serrano et al 2015). Detailed and modern morphological descriptions coupled with DNA sequence data currently available in public databases are facilitating the identification of taxa (Martin et al 2014;Phillips et al 2013).…”

“…The pathogen also affects other Mediterranean oak species such as Quercus afares, Q. canariensis, Q. coccifera, and Q. ilex (Linaldeddu et al 2009aTsopelas et al 2010). In recent years, D. corticola has caused concern in the United States, where it colonized aggressively Q. agrifolia, Q. rubra, and Q. virginiana (Aćimović et al 2016;Dreaden et al 2011;Lynch et al 2013). Despite the number of studies aimed at elucidating the taxonomy and pathogenicity of D. corticola, its evolutionary and geographical origins remain unresolved.…”

“…The effects of these factors have long been synthesized in a theoretical model that hypothesizes the succession of three different types of factors predisposing, inciting, and contributing (Manion 1991). It has, however, been shown that pathogens belonging to the genera Diplodia and Phytophthora have had a prominent role in the decline and mortality of oak trees in a variety of contexts Lynch et al 2013;Perez-Sierra et al 2013;Scanu et al 2013).…”

Investigation of the fungi associated with dieback of prickly acacia (Vachellia nilotica subsp. indica) in Northern Australia

“…In the presence of widespread stressors, these fungi can cause rapid dieback resulting in extensive losses over vast areas . Moreover, a number of Botryosphaeriaceae fungi are also well-recognized as plant pathogens having potential to cause significant disease symptoms in the absence of other stressors Lynch et al 2013;). …”

“…Different sap sucking insects can also impose serious stress which can cause or predispose the trees to dieback (Kunca & Leontovyc 2013;Kaczynski et al 2014;Neumann et al 2014). Several insects act as vectors to disseminate the virulent strains of different pathogens which also significantly contribute to the dieback process (Kamata et al 2002;Eskalen et al 2012;Eskalen et al 2013). Insect damage also provides entry sites for dieback and canker pathogens .…”