Abstract
Olive trees are infected and damaged by Botryosphaeriaceae fungi in various countries. The botryosphaeriaceous fungus Neofusicoccum mediterraneum is highly aggressive and is a major concern for olive groves in Spain and California (USA), where it causes ‘branch and twig dieback’ characterized by wood discoloration, bark canker, and canopy blight. During surveys of olive groves in Apulia (southern Italy), we noticed that—in some areas—trees were heavily affected by severe branch and twig dieback. In addition, chlorosis and the appearance of red-bronze patches on the leaf preceded the wilting of the foliage, with necrotic leaves persisting on the twigs. Given the severity of the manifestation in zones also subject to olive quick decline syndrome (OQDS) caused by Xylella fastidiosa subsp. pauca, we investigated the etiology and provide indications for differentiating the symptoms from OQDS. Isolation from diseased wood samples revealed a mycete, which was morphologically and molecularly identified as N. mediterraneum. The pathogenicity tests clearly showed that this fungus is able to cause the natural symptoms. Therefore, also considering the low number of tested samples, N. mediterraneum is a potential causal agent of the observed disease. Specifically, inoculation of the twigs caused complete wilting in two to three weeks, while inoculation at the base of the stem caused severe girdling wedge-shaped cankers. The growth rate of the fungus in in vitro tests was progressively higher from 10 to 30 °C, failing to grow at higher temperatures, but keeping its viability even after prolonged exposure at 50 °C. The capacity of the isolate to produce catenulate chlamydospores, which is novel for the species, highlights the possibility of a new morphological strain within N. mediterraneum. Further investigations are ongoing to verify whether additional fungal species are involved in this symptomatology.
Highlights
IntroductionThe olive tree (Olea europea L.) originated from the oleaster 6000–8000 years ago in the northeastern Levant territory of the Mediterranean basin, approximately in the area close to today’s Syria–Turkey border [1]
On the basis of these features and using the identification key to genera and species of Botryosphaeriaceae by Phillips et al [16], we identified the botryosphaeriaceous fungus as Neofusicoccum mediterraneum (Ascomycota; Pezizomycotina; Dothideomycetes; Dothideomycetes incertae sedis; Botryosphaeriales; Botryosphaeriaceae; Neofusicoccum)
The symptomatology—branch and twig dieback—that is emerging with severity in Apulia adds further worry for olive-growing already damaged by olive quick decline syndrome (OQDS)
Summary
The olive tree (Olea europea L.) originated from the oleaster 6000–8000 years ago in the northeastern Levant territory of the Mediterranean basin, approximately in the area close to today’s Syria–Turkey border [1]. As well as being a key feature of the Mediterranean landscape, olive tree cultivation reduces soil erosion—provided that cultivation is not highly intensive and mechanized and is performed in a no-tillage regime, namely with a ground plant cover. In this manner, it enables areas that are not suited to high-income agriculture to be recovered for farming [5]
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