Identification, pathogenicity and distribution of the causal agents of dieback in avocado orchards in Spain

Abstract

An increased incidence of dieback from branches in several avocado orchards in southern Spain was observed in 2014. Surveys were conducted from May to October 2014, sampling the affected branches to isolate the causal agents. A total of 68 fungal isolates, recovered from ten avocado orchards, were identified, by morphological characterisation and DNA sequencing, as belonging to the genera: Neofusicoccum parvum (50%), Colletotrichum gloeosporioides (17.6%), Neofusicoccum luteum (16.2%), Neofusicoccum australe (13.2%), Neofusicoccum mediterraneum (1.5%) and Lasiodiplodia theobromae (1.5%). A decreasing level of virulence in artificial inoculations on avocado plants was observed in N. parvum, N. luteum, N. mediterraneum, N. australe, C. gloeosporioides and L. theobromae, there were significant differences among N. parvum and the rest of species of this genus, and significant differences were only observed between N. luteum and C. gloeosporioides. The geographical distribution of N. parvum and N. Luteum covers different areas, while C. gloeosporioides and N. australe are located only in the areas around Benamocarra and Vélez-Málaga (southern Spain), while N. mediterraneum and L. theobromae appear only occasionally. This is the first study of avocado branch cankers in Spain which identifies the causal agents and establishes their pathogenicity groups, with N. parvum as the most important causal agent of avocado dieback in this area.

Phytophthora Root Rot Modifies the Composition of the Avocado Rhizosphere Microbiome and Increases the Abundance of Opportunistic Fungal Pathogens

“…These isolates mostly belonged to the genus Fusarium , which confirms the findings by Carranza-Rojas et al (2015) who found several Fusarium species (Hypocreales), among which F. solani and F. sambucinum , to be associated with avocado root rot. Other fungal genera such as Lasiodiplodia (Botryosphaeriales), Scytalidium (Helotiales) and Mortierella (Mortierellales) have been previously reported as avocado pathogens in Peru, Spain, South Africa and Mexico ( Alama et al, 2006 ; Coertzen and Fourie, 2017 ; Hernández Pérez et al, 2018 ; Arjona-Girona et al, 2019 ). Sequencing of the fungal microbiome confirmed that Helotiales and Mortierellales were dominant taxa in the rhizosphere of root rot symptomatic trees, which suggests that these taxa could act as opportunistic fungal pathogens following root rot infection.…”

Antifungal Agents Based on Chitosan Oligomers, ε-polylysine and Streptomyces spp. Secondary Metabolites against Three Botryosphaeriaceae Species

“…It is also worth noting that the three fungal species tested in the present study are not only pathogens of grapevine, but also of other commercially important woody plants. For instance, D. seriata and B. dothidea are phytopathogens of apple [22], N. parvum causes dieback in avocado [45], B. dothidea causes branch dieback of olive [46], and the three of them are associated with branch cankers on almond trees [47]. Consequently, the results of this study may also find application in other pathosystems, resulting in an even higher ecological and economic impact.…”

On the Applicability of Chitosan Oligomers-Amino Acid Conjugate Complexes as Eco-Friendly Fungicides against Grapevine Trunk Pathogens

“…[59], and even on woody crops of recent implantation and extension in Spain such as pistachio [60,61]. Furthermore, D. seriata and B. dothidea have been cited as phytopathogens on apple [62], while N. parvum causes avocado dieback [63], B. dothidea causes Botryosphaeria blights and cankers on olive trees [64], and as mentioned, the three of them are commonly related to branch cankers on almond trees [54]. Therefore, the findings obtained in the present study may also be applied and extended to other basic Mediterranean crops that usually share these types of pathogens.…”