Abstract
Colletotrichum acutatum is a serious concern for the Portuguese oliviculture and food industry, due to both olive oil yield and quality decrease. While the organism’s phytopathogenic potential has been well documented, the pathogen adhesion and colonization process in olives remain poorly understood. This paper reports experiments conducted on C. acutatum-susceptible, C. acutatum-moderately resistant and C. acutatum-resistant olive fruits during infection process, in two consecutively years, to identify the physical differences related to the host cuticle promoting resistance and susceptibility to C. acutatum. Cuticle thickness, perimeter and area of epidermal cells of ‘Galega’ (susceptible), ‘Cobrancosa’ (moderate-resistant) and ‘Picual’ (resistant) fruits were measured. Here, we also describe the colonization process of olive fruits by C. acutatum. To achieve this goal olive fruits from ‘Galega’, ‘Cobrancosa’ and ‘Picual’ were inoculated in a field trial with an aqueous suspension of C. acutatum (1x106 spores ml-1) under suitable humidity and temperature conditions. Light, fluorescent and scanning electron microscopy were used to view olive fruit sections. Significant differences were observed among the parameters studied: cuticle thickness, perimeter and area of olive fruit epidermal cells. The C. acutatum-resistant (‘Picual’) fruits showed highest mean values for each parameter in both years. Pathogen ultrastructures, such as spores, germ tube, and appressoria were clearly observed using different microscopy techniques. Acervuli sporulation was observed only 192 hours after inoculation in C. acutatum-susceptible (‘Galega’) fruits.
Highlights
The Colletotrichum acutatum and C. gloeosporioides caused anthracnose in a wide range of hosts found mainly in temperate, subtropical and tropical areas (Martín and García-Figueres, 1999; Moral et al, 2009)
The mesocarp of susceptible fruits became densely infected, dehydrated, and necrotic lesions and hyphae became visible under scanning electron microscopic (SEM) (Figure 1b, 1c)
Olive anthracnose is caused by C. acutatum and C. gloeosporioides (Martín and García-Figueres, 1999; Angiolillo et al, 1999; Kimura et al, 2001; Trapero, 2009)
Summary
The Colletotrichum acutatum and C. gloeosporioides caused anthracnose in a wide range of hosts found mainly in temperate, subtropical and tropical areas (Martín and García-Figueres, 1999; Moral et al, 2009). In national terms the prevalent olive cultivar is ‘Galega’ that gives to olive oil a good specificity when compared with olive oils from others cultivars. This cultivar have a sanitary problem that is the susceptibly to olive anthracnose caused by the C. acutatum, named in Portugal by ‘gafa’. The olive anthracnose disease was firstly reported in Portugal by Almeida (1899). This disease is very aggressive and is one of the main constraints affecting both the olive production and oil quality (Talhinhas et al, 2003, 2005, 2007; Carvalho et al, 2008). The disease is distributed along all Mediterranean Basin it is in Portugal that it has a great expression, mainly due to the Atlantic influence (higher moisture during autumn)
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