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 ).

However, avocado production is decreasing all over the world due to branch cankers and fruit stem-end rot. Symptomatic trees exhibit red-brown cankers and dieback on branches associated with a characteristic white exudate ( McDonald & Eskalen, 2011 ). The first stages of infection are often caused by mechanical injuries, which allow the access of pathogens. 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.

In Spain, other subtropical crops different to avo‑­cado, such as loquat ( Eribotrya japonica Lindl.), are affected by species of Botryosphaeriaceae , among them, Diplodia malorum Fuckel, Diplodia olivarum A.J.L. Phillips, Frisullo & Lazzizera, Diplodia seriata De Not., species of complex Diplodia pseudoseriata/Diplo­dia alatafructa, Diplodia sp., Dothiorella sar­mentorum (Fr.) A.J.L. Phillips, Alves & Luque, Neo­fusicoccum mediterraneum Crous, Wingf & A.J.L. Phillips, Neo­fusicoccum parvum (Pennycook & Samuels) Crous, Slippers & A.J.L. Philips, Spencermartinsia plurivora Abdollahz., Javadi & A.J.L. Phillips and Spencermartinsia viticola (A.J.L. Phillips & J. Luque) A.J.L. Phillips, A. Alves & Crous ( González-Domínguez et al ., 2017 ). In this crop, other pathogens, namely Alter­naria alternata (Fr.) Keissl., Penicillium expansum Link, Botrytis cinerea Pers., Colletotrichum gloeosporioides (Penz.) Penz. & Sacc., Pestalotiopsis clavispora (G.F. Atk.) Steyaert and D. seriata caused post-harvest diseases ( Palou et al ., 2016 ). Other Mediterranean crops such as almond ( Prunus dulcis Webb) are also affected by fungi Botryosphaeriaceae ( Gramaje et al ., 2012 ) and N. mediterraneum and Botryosphaeria dothidea (Moug. ex Fr.) Ces. & De Not. have been isolated from olive ( Olea europaea L.) branches ( Moral et al ., 2017 ) and N. parvum from mango ( Mangifera indica L.) trees ( Arjona-Girona & López-Herrera, 2016 ).

Colletotrichum gloeosporioides and N. parvum have been described as causal agents of anthracnose and stem end rot in avocado fruit (cv. Hass) in Turkey ( Akgül & Awan, 2016 ). N. parvum and D. seriata caused dieback in grapevine ( Vitis vinifera L.) ( Spagnolo et al ., 2017 ). Over the last two decades, significant losses have been recorded in citrus production in Portugal from anthracnose symp­toms caused by C. gloeosporioides ( Ramos et al ., 2016 ).

Neofusicoccum parvum ,  Neofusicoccum luteum (Penny­cook & Samuels) Crous, Slippers & A.J.L. Phillips and Neofusicoccum australe (Slippers, Crous & M.J. Wingf.) Crous, Slippers & A.J.L. Phillips were identified in California ( McDonald et al ., 2009 ). N. parvum was also found in Mexico ( Molina-Gayosso et al ., 2012 ), mainly affecting fruits, and Lasiodiplodia theobromae (Pat.) Griffon & Maubl. in Peru ( Alama et al ., 2006 ). Although the most important post-harvest disease in Chile is anthracnose, caused by C. gloeosporioides , a new disease caused by N. australe was also found ( Montealegre et al ., 2016 ).

The aims of this work were to study the distribution of avocado trees affected by branch cankers in commercial orchards in southern Spain, identify their fungal agents and establish their virulence groups.

This study shows the incidence and diversity of fungal isolates associated with avocado dieback in commercial orchards in southern Spain. The list in­cludes different genera ( Neofusicoccum, Colletotri­chum and Lasiodiplodia ) and species ( N. parvum, N. luteum, N. mediterraneum, N. australe, C. gloeos­porioides and L. theobromae ) that are also usually involved in dieback in avocado orchards in other countries ( McDonald & Eskalen, 2011 ).

Neofusicoccum parvum is the most abundant spe­cies, with an incidence of 50%, followed by  C. gloeosporioides with 18%, N. australe and N. luteum with 13% and 16%, respectively, and finally,  N. mediterraneum  and  L. theobromae , which appear only occasionally with an incidence of 1.5% in each case. Our results agree with the greater incidence of the species N. parvum and N. australe associated with almond orchards in other areas of Spain ( Gramaje et al ., 2012 ). N. parvum is consi­de­red the most common species associated with grapevine decline syndrome ( Armengol et al ., 2001 ; Aroca et al ., 2006 ) and N. mediterraneum  was also isolated from olive fruits in southern Spain, showing symptoms of Dalmatian disease ( Moral et al ., 2010 ).

In other countries, N. parvum , N. luteum and N. australe associated with avocado dieback have also been described in California ( McDonald et al ., 2009 ). Typical Dothiorella canker symptoms observed inclu­ded darkened and friable bark showing a dry, white, powdery exudate. These studies concluded that the higher incidence of these pathogens is a consequence of the high-density planting frequent in Californian avocado crops and they recommend more suitable management strategies ( McDonald & Eskalen, 2011 ). N. luteum was identified in California as the main cause of stem-end rot in harvested avocado fruit (65%), followed by C. gloeosporioides with an incidence of 35% ( Twizeyimana et al ., 2013 ). In the same way, the fungi detected in avocado branch cankers in Spain could also affect the fruit directly, leading to a fall in production. L. theobromae has been also described as the causal agent of avocado dieback in Peru ( Alama et al ., 2006 ). The symptoms of cankers and red-brown lesion with white exudates observed after artificial inoculation were similar to natural infection. There are other examples in which species of these genera have been associated to avocado causing anthracnose and stem-end rot in Turkey ( Akgül & Awan, 2016 ), or to other plants such as oak ( Quercus robur L.) in Portugal ( Barradas et al ., 2013 ) and olive in Tunisia ( Triki et al ., 2015 ) causing dieback, or shoot blight and plant decay on pomegranate ( Punica granatum L.) in Italy ( Riccioni et al ., 2017 ).

In our study, we conclude that N. parvum and N. luteum are widely extended, while C. gloeosporioides and N. australe are located only in the biggest areas, which could be due to the wider dispersion or higher production of conidia of N. parvum and N. luteum . Future experiments should be carried out using spore trapping ( Eskalen et al ., 2013 ) to confirm this theory. Our results, showing the greater virulence of isolates of N. parvum and N. luteum when compared with C. gloeosporioides and the greater virulence of N. parvum vs N. australe , coincide with the results of Eskalen et al . (2013) , who reported that lesions caused by N. parvum and N. luteum were larger than those caused by N. australe . N. mediterraneum and L. theobromae appeared occasionally, but did not appear to be a great threat.

Although N. parvum has been previously described in avocado ( Zea-Bonilla et al ., 2007 ) and in other crops such as blueberry ( Vaccinium spp.) ( Castillo et al ., 2013 ) and mango ( Arjona-Girona & López-Herrera, 2016 ) on the southern coast of Andalusia, Spain, an increased incidence of dieback on branches in avocado orchards has been observed and this could constitute a serious threat, in a similar way to N. luteum, N. australe and C. gloeosporioides , to the yield of avocado orchards in this area. The fungal inoculum tends to increase due to the poor management of pruning remains, which are often shredded and mixed into the soil instead of being burned, as famers usually do in this area.

This is the first study of avocado cankers on branches in southern Spain which evaluates the causal agents and establishes its pathogenicity groups. N. parvum is the most abundant species observed, and is the most important causal agent of dieback avocado in this area. N. luteum, N. australe and C. gloeosporioides showed the lower incidence as causal agents of the disease.

The authors thank the staff of TROPS of Vélez-Malaga (Spain) for their technical assistance in avocado orchard surveys for this study.