Comparative Analysis of Secondary Metabolites in Diplodia corticola Strains with Different Virulence Degrees Associated with Canker and Dieback of Quercus spp.

Diplodia corticola is one of the most aggressive fungal pathogens of Quercus species involved in the decline of Mediterranean oak forests. In this study, three strains of D. corticola associated with holm (Quercus ilex) and cork (Quercus suber) oak trees exhibiting dieback symptoms and cankers in Algeria were selected to investigate the production of secondary metabolites. Metabolomic analyses revealed the production of several known compounds, such as sphaeropsidins, diplopyrones and diplofuranones. Moreover, the comparative investigation of secondary metabolites produced by the analyzed strains with different degrees of virulence revealed possible implications of these compounds in the fungal virulence. In particular, sphaeropsidins seem to be the main phytotoxic compounds of D. corticola involved in the infections of Quercus species, with a possible synergistic influence of the less representative compounds in the fungal virulence.

First report of 6-methylpyridione analogues from Dothiorella sarmentorum, a botryosphaeriaceous fungus associated with grapevine trunk diseases.

Dothiorella species are fungal plant pathogens associated with Botryosphaeria dieback of grapevine. Symptoms caused by these fungi on grapevines suggest possible implication of phytotoxic metabolites in the infection mechanisms. However, few studies were conducted to investigate the secondary metabolism of these fungi. In this study, 6-methylpyridione analogues were isolated and identified for the first time in liquid cultures of Dothiorella sarmentorum isolated from symptomatic grapevine in Algeria.

Mitidjospirone, a new spirodioxynaphthalene and GC-MS screening of secondary metabolites produced by strains of Lasiodiplodia mitidjana associated to Citrus sinensis dieback.

Mitidjospirone, a new spiridioxynaphthalene, was isolated from the mycelial extract of a strain of Lasiodiplodia mitidjana, a recently described species belonging to the family Botryosphaeriaceae. Its structure was elucidated by extensive spectroscopic analysis and the absolute configuration was determined by electronic circular dichroism (ECD) experiment. Furthermore, several known compounds were identified during the screening of secondary metabolites produced by four strains of L. mitidjana.

Secondary Metabolites, including a New 5,6-Dihydropyran-2-One, Produced by the Fungus Diplodia corticola. Aphicidal Activity of the Main Metabolite, Sphaeropsidin A.

An undescribed 5,6-dihydropyran-2-one, namely diplopyrone C, was isolated and characterized from the cultures of an isolate of the fungus Diplodia corticola recovered from Quercus suber in Algeria. The structure and relative stereostructure of (5S,6S,7Z,9S,10S)-5-hydroxy-6-(2-(3-methyloxiran-2-yl)vinyl)-5,6-dihydro-2H-pyran-2-one were assigned essentially based on NMR and MS data. Furthermore, ten known compounds were isolated and identified in the same cultures. The most abundant product, the tetracyclic pimarane diterpene sphaeropsidin A, was tested for insecticidal effects against the model sucking aphid, Acyrthosiphon pisum. Results showed a toxic dose-dependent oral activity of sphaeropsidin A, with an LC50 of 9.64 mM.

Cadophora sabaouae sp. nov. and Phaeoacremonium Species Associated with Petri Disease on Grapevine Propagation Material and Young Grapevines in Algeria.

A field survey conducted on asymptomatic grapevine propagation material from nurseries and symptomatic young grapevines throughout different regions of Algeria yielded a collection of 70 Phaeoacremonium-like isolates and three Cadophora-like isolates. Based on morphology and DNA sequence data of ß-tubulin (tub2) and actin, five Phaeoacremonium species were identified including Phaeoacremonium minimum (22 isolates), Phaeoacremonium venezuelense (19 isolates), Phaeoacremonium parasiticum (17 isolates), Phaeoacremonium australiense (8 isolates), and Phaeoacremonium iranianum (4 isolates). The latter two species (P. australiense and P. iranianum) were reported for the first time in Algeria. Multilocus phylogenetic analyses (internal transcribed spacer, tub2, and translation elongation factor 1-α) and morphological features, allowed the description of the three isolates belonging to the genus Cadophora (WAMC34, WAMC117, and WAMC118) as a novel species, named Cadophora sabaouae sp. nov. Pathogenicity tests were conducted on grapevine cuttings cultivar Cardinal. All the identified species were pathogenic on grapevine cuttings.

Lasiodiplodia mitidjana sp. nov. and other Botryosphaeriaceae species causing branch canker and dieback of Citrus sinensis in Algeria.

Several Botryosphaeriaceae species are known to occur worldwide, causing dieback, canker and fruit rot on various hosts. Surveys conducted in ten commercial citrus orchards in the northern region of Algeria revealed five species of Botryosphaeriaceae belonging to three genera associated with diseased trees. Morphological and cultural characteristics as well as phylogenetic analyses of the internal transcribed spacer (ITS) region and the translation elongation factor 1-alpha (tef1-α) identified Diplodia mutila, Diplodia seriata, Dothiorella viticola, Lasiodiplodia mediterranea and a novel species which is here described as Lasiodiplodia mithidjana sp. nov.. Of these, L. mithidjana (14.1% of the samples) and L. mediterranea (13% of the samples) were the most widespread and abundant species. Pathogenicity tests revealed that L. mediterranea and D. seriata were the most aggressive species on citrus shoots. This study highlights the importance of Botryosphaeriaceae species as agents of canker and dieback of citrus trees in Algeria.