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

Isabel Arjona-Girona,Carlos J López-Herrera,David Ruano-Rosa

doi:10.5424/sjar/2019171-13561

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.

Highlights

The avocado (Persea americana Mill.) is cultivated worldwide, but was commercially produced in Europe for the first time in Spain
After the macroscopic fungal identification of the morphological characters of 68 isolates and their subsequent confirmation by DNA sequence analyses, all the isolates were identified as belonging to the genera Neofusicoccum, Colletotrichum and Lasiodiplodia, with six different species in different proportions: N. parvum (50%), C. gloeosporioides (18%), N. australe (13%), N. luteum (16%), N. mediterraneum (1.5%) and L. theobromae (1.5%) (Table 2)
We evaluated the pathogenicity of the different species of the Neofusicoccum genus (F=20.03; df=3, 276; p

Summary

Introduction

The avocado (Persea americana Mill.) is cultivated worldwide, but was commercially produced in Europe for the first time in Spain. In the 1970s, commercial avocado orchards were established in southern Spain (provinces of Málaga and Granada) because the microclimate in this area bears similarities to the conditions in different regions of America, such as Mexico, Peru and California, which have a long tradition of growing this crop, with high levels of production (http://faostat3.fao.org/browse/Q/QC/E). Avocado production is decreasing all over the world due to branch cankers and fruit stem-end rot. Avocado dieback has been observed in different countries with tropical and subtropical climate, such as Chile (Auger et al, 2013) and Colombia (Burbano-Figueroa et al, 2018) in South America or Spain (Zea-Bonilla et al, 2007) in Europe, and many fungal agents have been identified, especially those belonging to the Botryosphaeriaceae family

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