Abstract
The black-banded oak borer, Coraebus florentinus, is an emerging pest of oak trees in the western Mediterranean region. Larvae of the insect are xylophagous and progressively excavate an annular gallery that interrupts sap flow, resulting in the death of the attacked branches. Until now, limited information has been available regarding the ecological interactions between C. florentinus and the main plant pathogenic fungi involved in the etiology of oak decline. Knowledge of these interactions is important in understanding their impact in natural ecosystems and developing appropriate management strategies. Therefore, in this study, we characterized the fungal communities occurring in the exoskeleton of adults and larvae of C. florentinus and associated with the necrotic wood tissues surrounding the branch galleries of declining oak trees. A total of 29 fungal species were identified based on DNA sequence data and morphological features, of which 14 were from symptomatic woody tissues, six from insect exoskeleton, and nine from both insects and symptomatic wood tissues. The most frequent fungal species, Cryphonectria naterciae (15.9% of isolates), Dothiorella iberica (11.3%), and Diplodia corticola (9.9%), were isolated from both insect and gallery systems. All three species are well-known oak pathogens and are reported here, for the first time, to be associated with C. florentinus. At the same time, 89.6% of the fungal taxa were isolated from one or two sites, highlighting the site-dependence of fungal community assemblages.
Highlights
Over the past 30 years, Mediterranean oak forest ecosystems have been greatly impacted by severe decline phenomena and extensive mortality events, revealing the high vulnerability of these formations [1,2,3]
From autumn 2016 to spring 2017, oak trees that had been attacked by C. florentinus at each site were identified by the presence of bored branches (4–7 cm in diameter) showing dead leaves still attached scattered among healthy foliage (Figure 1)
Fungal Community Diversity communities associated with C. florentinus attacks in declining oak woodlands in Sardinia, The Shannon diversitythe index value was for the of fungal associated contributing to expanding knowledge on highest the bioecology this community emerging insect pest inwith the symptomatic wood tissues surrounding feeding galleries on to oak branches
Summary
Over the past 30 years, Mediterranean oak forest ecosystems have been greatly impacted by severe decline phenomena and extensive mortality events, revealing the high vulnerability of these formations [1,2,3]. Severe decline and mortality events have the potential to drastically alter oak ecosystems, with important implications for the plant community dynamics, soil carbon–water balance, and structure and composition of soil food webs [4,5,6,7]. Oak decline is commonly considered a multifactorial disease in which many interacting abiotic and biotic factors such as drought, frost, insect pests and pathogens variable in intensity and frequency even at site level are involved [8,9,10,11,12,13]. Among the biotic factors involved in the onset of oak decline events, several invasive insects, fungi, and oomycetes play a primary role. In recent years, Forests 2019, 10, 488; doi:10.3390/f10060488 www.mdpi.com/journal/forests
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