Olive Twig and Branch Dieback in California Caused by Cytospora oleicola and the Newly Described Species Cytospora olivarum sp. nov.

Abstract

<jats:p> Field surveys conducted throughout California olive-growing regions in 2008 and 2009 resulted in a collection of 101 Cytospora-like isolates from olive twig and branch dieback symptoms. Cytospora isolates were isolated from multiple cvs. in different olive orchards in Fresno, Madera, Merced, Napa, Riverside, Santa Barbara, Sonoma, Tulare, and Ventura counties. Taxonomic studies of macro- and microscopic structures along with multigene phylogenetic analyses of the internal transcribed spacer region, including the 5.8S rDNA (ITS1–5.8S–ITS2), and fragments of the translation elongation factor 1-α, beta-tubulin, and actin genes identified two species, Cytospora oleicola and C. olivarum sp. nov. Pathogenicity studies conducted in mature olive trees cvs. Manzanillo and Sevillano showed both species to be pathogenic and able to cause vascular necrosis and cankers in olive branches. This study adds to the current knowledge on the etiology of olive twig and branch dieback and provides new important information for the development of effective control strategies against canker diseases affecting olive in California. </jats:p>

Endophytic Fungi of Olive Tree

“…Other recent reports concern Diaporthe ambigua causing twig cankers in Italy [ 52 ] and Neofabraea kienholzii causing leaf and shoot lesions in California [ 53 ], while Cytospora pruinosa recovered from plants showing branch dieback symptoms in Spain was found not to be pathogenic [ 54 ]. Notwithstanding, reports concerning Cytospora [ 30 , 35 ] must be taken with caution, considering recent assessments of pathogenicity on olive tree by a few Cytospora spp., including the novel species C. olivarum [ 55 , 56 ].…”

Dieback and decline pathogens of olive trees in South Africa

“…from almost 30 % of twig dieback and canker samples. Pathogenicity trials illustrated the ability of C. oleicola and C. olivarum to cause lesions when inoculated on olive branches ( Úrbez-Torres et al 2020 ); however, the reported lesion size was considerably smaller than that reported for some species of Botryosphaeriaceae by Úrbez-Torres et al (2013) . In Italy, Pleurostoma richardsiae , Phaeoacremonium spp., and members of the Botryosphaeriaceae have been identified as the most prevalent fungi associated with olive decline ( Carlucci et al 2013 , 2015 , Nigro et al 2013 ).…”

“…In addition to the above-mentioned pathogens, species of Basidiomycota , Botryosphaeriaceae , Cytospora , Diaporthe , Diatrypaceae , Phaeoacremonium , Phaeomoniellales , and some other fungi such as Comoclathris incompta (= Phoma incompta ), and Pleurostoma richardsiae , have also been associated with various decline-related symptoms of olive trees in Croatia, Greece, Italy, New Zealand, Spain, and the USA ( Rumbos 1988 , 1993 , Taylor et al 2001 , Carlucci et al 2008 , 2013 , 2015 , Moral et al 2010 , 2017 , Kaliterna et al 2012 , Nigro et al 2013 , Úrbez-Torres et al 2013 , 2020 , Lawrence et al 2018 ). Úrbez-Torres et al (2013) identified 18 fungal species in a survey of fungi causing olive twig and branch dieback in California (USA), of which the Botryosphaeriaceae were found to be the most prevalent, followed by species of Diaporthe and the Diatrypaceae .…”

“… Moral et al (2010) also found N. mediterraneum to be an aggressive pathogen when inoculated on olive branches. More recent studies have also associated Cytospora oleicola , C. olivarum , C. plurivora , and C. sorbicola with branch cankers and dieback of olive trees in the USA ( Lawrence et al 2018 , Úrbez-Torres et al 2020 ). In some counties of California, Úrbez-Torres et al (2020) recovered Cytospora spp.…”

“…More recent studies have also associated Cytospora oleicola , C. olivarum , C. plurivora , and C. sorbicola with branch cankers and dieback of olive trees in the USA ( Lawrence et al 2018 , Úrbez-Torres et al 2020 ). In some counties of California, Úrbez-Torres et al (2020) recovered Cytospora spp. from almost 30 % of twig dieback and canker samples.…”