Infection Process of Olive Fruits by Colletotrichum acutatum and the Protective Role of the Cuticle and Epidermis

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), 'Cobrançosa' (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 102 from 'Galega', 'Cobrançosa' and 'Picual' were inoculated in a field trial with an aqueous suspension of C. acutatum (1x10 6 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.

Virulence diversity of anthracnose pathogens (Colletotrichum acutatum and C. gloeosporioides species complexes) on eight olive cultivars commonly grown in Portugal

“…This corroborates field experience of high anthracnose susceptibility of 'Maçanilha de Tavira' and 'Galega Vulgar', and of resistance attributed to 'Blanqueta', 'Negrinha de Freixo' and 'Picual' (Mateo-Sagasta 1968;Leitão et al 1986;Moral et al 2008;Gomes et al 2012). 'Cordovil de Serpa' revealed an intermediate behaviour.…”

“…In fact, the analysis of the correlation between disease severity and either conidia germination or appressoria formation revealed that the final outcome of the disease severity was, in part (up to 30 %), due to the initial hostpathogen recognition events. No differences could be detected in the histopathological comparison of the infection processes between compatible and incompatible interactions (Gomes et al 2012). However, present results suggest that specific recognition events may be occurring at an early stage, conditioning spore germination and appressorium formation, which in turn can condition the disease severity.…”

Chili anthracnose: Colletotrichum taxonomy and pathogenicity

“…Once penetration succeeds, the pathogen colonizes the host cells, which then become densely infected, and finally necrotic lesions and hyphae become visible (Gomes et al, 2012). Secondary hyphae grow extensively inter-and intracellularly across cell walls.…”

Unsaturated Lipids Change in Olive Tree Drupe and Seed during Fruit Development and in Response to Cold-Stress and Acclimation

“…Moreover, in numerous plants, the formation of a thicker cuticle also occurs as a protection to cold-induced winter drought [53]. Leaf and fruit cuticles generally contain the same classes of compounds, however, genotype-specific-changes are possible, as, in fact, occurs in olive trees in response to drought and pathogens [52,54]. In a previous paragraph, it has been shown that cutinosomes, enriched in C18:2-FA, are extruded by the seed coat to the endosperm to cause an indirect protection for desiccation to the non-cutinised embryo, with osmotin involved in this lipid-trafficking (Figure 2I).…”