Morphological, Pathogenic, and Molecular Characterization of Colletotrichum acutatum Isolates Causing Almond Anthracnose in Spain

Abstract

Almond anthracnose is a serious and emerging disease in several countries. All isolates causing almond anthracnose have been assigned to the Colletotrichum acutatum species complex, of which only C. fioriniae and C. godetiae have been associated with the disease to date. Here, we characterized Colletotrichum isolates from almond fruit affected by anthracnose in the Andalusia region. Two Colletotrichum isolates causing olive anthracnose were included for comparison. Morphological characteristics were useful for separating the isolates into groups based on colony morphology. Pathogenicity tests in almond, olive, and apple fruit showed differences in virulence and some degree of pathogenic specialization among isolates. Molecular characterization allowed clear identification of the Colletotrichum isolates tested. The olive isolates were identified as C. godetiae and C. nymphaeae, both previously identified in Andalusian olive orchards. Two phylogenetic species were identified among the almond isolates: C. godetiae, with gray colonies, which is well known in other countries, and C. acutatum, with pink-orange colonies. This species identification differs from those of pink-colony subpopulations described in other countries, which are C. fioriniae. Therefore, this study is also the first report of a new species of Colletotrichum causing almond anthracnose within the C. acutatum species complex.

Olive anthracnose: a yield‐ and oil quality‐degrading disease caused by several species of Colletotrichum that differ in virulence, host preference and geographical distribution

“…is also commonly associated with anthracnose symptoms in oleander in Portugal (A. P. Ramos, personal communication, Instituto Superior de Agronomia, Universidade de Lisboa; Lisbon, Portugal), although, in olive, it is restricted to the southernmost region of this country, the Algarve (Talhinhas et al ., ). This fungus also seems to be emerging as a causal agent of almond anthracnose in Andalucia (Spain), but not in olive (López‐Moral et al ., ). Colletotrichum theobromicola Delacr., recently detected in Australia associated with olive anthracnose (Schena et al ., ), could be an emergent olive pathogen in this country, where C. acutatum s.s .…”

Almond Anthracnose: Current Knowledge and Future Perspectives

“…Since then, the disease has been detected regularly in commercial orchards across the Guadalquivir valley, showing higher outbreaks with favorable environmental conditions for disease development. The latest major outbreak of AA was reported in spring of 2014 in southern Spain (provinces of Huelva and Sevilla), when the disease was considered as re-emerging in this country [9].…”

“…The last one is considered a major disease of this crop worldwide causing important economic losses when serious outbreaks occur [8]. Nevertheless, almond anthracnose (AA) has been considered a secondary disease in specific almond-growing areas across the Mediterranean Basin (i.e., Italy and southern Spain) until its recently re-emergence as a consequence of the new establishment of almond plantings in non-traditional almond-growing areas [9,10].…”

Water Stress Enhances the Progression of Branch Dieback and Almond Decline under Field Conditions

“…They include dense planting, high levels of irrigation-water and fertilization, pruning- and harvest-mechanization, and a high number of pesticide treatments preventing pest and plant diseases [ 3 ]. As a consequence of this new scenario, the occurrence of secondary almond diseases, as well as emerging ones, have been reported recently in the new almond growing regions across the Guadalquivir Valley in Andalusia region [ 3 , 4 , 5 ].…”

“…Among the emerging diseases already described in this geographic area [ 3 , 4 , 5 ], a new tree decline syndrome stands out in the new intensive almond plantings. It includes a broad diversity of symptoms, such as gummosis, shoot blight, defoliation, branch dieback, canker formation, internal wood discoloration and tree death.…”