Mecanismos físico-químicos de defesa ao Colletotrichum acutatum em frutos de oliveira produzidos na Região Sul do Uruguai.

Abstract

Olive Anthracnose, caused by Colletotrichum spp., is a significant fungal disease in olive-growing regions that leads to fruit rot, compromising both production and quality. The level of resistance among cultivars varies according to genetic factors and the stage of fruit maturation. This study aimed to identify the susceptibility levels of four olive cultivars (Arbequina, Picual, Frantoio, and Manzanilla de Sevilla) to Colletotrichum acutatum at two stages of fruit maturation: green and mature. Additionally, the study sought to investigate the role of cuticle thickness and total phenolic compound content as defensive mechanisms involved in the susceptibility of fruits to anthracnose at both maturation stages. The research was conducted at the National Institute of Agricultural Research - INIA Las Brujas - Canelones Department, Uruguay, in 2023 and 2024. The experimental design was completely randomized, consisting of four blocks. Green and mature fruits were inoculated with a fungal solution of 1x10^5 spores/mL and incubated for 15 days alongside control material. During this period, the development and progression of the fungus were periodically assessed at 2, 3, 4, 5, 7, 10, 11, 12, 13, and 15 days postinoculation, based on disease incidence and severity. For the anatomical analysis of the cuticle, fruits were sectioned at the equatorial region and infiltrated with liquid paraffin at 60 ºC using an automatic sample preparation system, carousel type, SLEEMTP. After infiltration, the segments were subjected to paraffin embedding using the YDL-6L model equipment from YIDI. After 24 hours, the segments were cut using a manual rotary microtome SLEE, Model CUT 4062, followed by slide mounting.Subsequently, the slides were stained with Safranin. Images were obtained via optical microscopy, and cuticle thickness was measured using the free software ImageJ. The thickness was determined by the width and length of the cuticle of the fruits, based on a set of six consecutive epidermal cells. Total phenolic compounds were quantified in healthy fruits using spectrophotometry, following the Folin-Ciocalteau methodology. Disease incidence and severity showed significant variations among cultivars at the green stage. However, in mature fruits, disease severity was uniform across cultivars. Susceptibility to anthracnose varied among cultivars in green fruits, while no significant differences were observed in mature fruits. Both cuticle thickness and total phenolic compounds varied among cultivars and maturation stages. In green fruits, the Frantoio cultivar was the least susceptible to anthracnose, while Arbequina and Picual showed moderate susceptibility, and Manzanilla was the most susceptible. In mature fruits, all cultivars were equally susceptible. The physical-chemical mechanisms did not influence the susceptibility of the fruits.